| 1. |
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| 2. |
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| 3. |
- Danielsson, Erik, et al.
(författare)
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A 4H-SiC BJT with an epitaxially regrown extrinsic base layer
- 2005
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 483, s. 905-908
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Tidskriftsartikel (refereegranskat)abstract
- 4H-SiC BJTs were fabricated using epitaxial regrowth instead of ion implantation to form a highly doped extrinsic base layer necessary for a good base ohmic contact. A remaining p(+) regrowth spacer at the edge of the base-emitter junction is proposed to explain a low current gain of 6 for the BJTs. A breakdown voltage of 1000 V was obtained for devices with Al implanted JTE.
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| 4. |
- Danielsson, Örjan, et al.
(författare)
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Reducing stress in silicon carbide epitaxial layers
- 2003
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 252:1-3, s. 289-296
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Tidskriftsartikel (refereegranskat)abstract
- A susceptor for the epitaxial growth of silicon carbide, with an up-lifted substrate holder, is investigated and compared to other susceptor designs both experimentally and by the use of computational fluid dynamics simulations. It is shown that the wafer bending due to temperature gradients is diminished in a hot-wall reactor compared to growth in a cold-wall reactor. The substrate backside growth is diminished using the up-lifted substrate holder, limiting the substrate bending due to the backside growth. Thereby the stress built into the epitaxial layers during growth is significantly reduced. Simulations indicate a lower effective C/Si ratio over the wafer, and a lower preferable growth temperature, as compared to the original susceptor design. In addition a slightly higher growth rate is achieved
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| 5. |
- Emtner, Margareta, et al.
(författare)
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Effect of physical training on fat-free mass in patients with chronic obstructive pulmonary disease (COPD)
- 2015
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Ingår i: Upsala Journal of Medical Sciences. - : Uppsala Medical Society. - 0300-9734 .- 2000-1967. ; 120:1, s. 52-58
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Tidskriftsartikel (refereegranskat)abstract
- Background. Weight loss and depletion of fat-free mass are common problems in patients with chronic obstructive pulmonary disease (COPD) and are related to muscular weakness and exercise intolerance. Physical training of COPD patients has good effect on exercise tolerance and quality of life. The aim of this study was to examine factors that affect change in fat-free mass after physical training, in patients with COPD.Patients. Patients were examined before and after a 4-month exercise period. Weight and height were measured, and bioelectrical impedance was performed. Fat-free mass (FFM) was calculated, by a three-compartment model, and fat-free mass index (FFMI) was calculated as FFM kg/m(2) and body mass index (BMI) as kg/m(2). A symptom-limited ramp ergometer test and 12-minute walk test (12MWT) were performed. Dyspnoea score of daily activities was determined by Chronic Respiratory Disease Questionnaire (CRDQ). Blood was taken for analyses of C-reactive protein (CRP) and fibrinogen. Patients with a BMI <21 kg/m(2) were given nutritional support during the training period.Results. A total of 27 patients completed the training (64 years, FEV1 31% of predicted). Patients with low FFMI gained 1.2 kg, whereas those with normal FFMI lost 0.7 kg (p = 0.04). In multivariate analyses high age (p = 0.03), low FEV1 (p = 0.02), and a high level of dyspnoea (p = 0.01) at baseline were found to be negative predictors for increase in FFM. Conclusions. Difficulties in increasing the fat-free mass in COPD patients by physical training seem to be associated with dyspnoea in daily life and impaired lung function (FEV1).
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| 6. |
- Emtner, Margareta I., et al.
(författare)
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Walking distance is a predictor of exacerbations in patients with chronic obstructive pulmonary disease
- 2007
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Ingår i: Respiratory Medicine. - : Elsevier BV. - 0954-6111 .- 1532-3064. ; 101:5, s. 1037-1040
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Tidskriftsartikel (refereegranskat)abstract
- Background: Patients with chronic obstructive pulmonary disease (COPD) are responsible for a high utilisation of the health care resources, and the cost is expected to increase. Physiological measures of lung function often fail to describe the impact the symptoms have on exacerbations, days of hospitalisation, and on a patient's health. Methods: Twenty-one patients (14 female) with COPD (65 years, 40-79 years) admitted to the Department of Respiratory Medicine in Uppsala, performed a pulmonary function test (FEV1% predicted=37) and health status measurement (St. Georges Respiratory Questionnaire, SGRQ) at discharge. Four to six weeks after discharge, when they were in a stable clinical condition, they performed an exercise test (Incremental Shuttle Walk Test, ISWT) to measure their exercise capacity. Results: Nine of 21 patients (43%) were rehospitalised within 12 month. The mean distance walked in the ISWT was 174 m in patients who were hospitalised and 358 m in non-hospitalised patients (P<0.001). Oxygen saturation ≤88% after the ISWT was found in 73% of hospitalised patients in contrast to only 22% in non-hospitalised patients (P<0.05). Activity related health status (SGRQ-activity) was higher (worse) in hospitalised patients than in non-hospitalised patients (75 vs. 50) (P<0.05). The association between walking distance and the risk of rehospitalisation was significant after adjusting for oxygen saturation and health status (hazard risk ratio 0.8 (0.67-0.97) per 10 m). This study has shown that walking distance is a good and reliable predictor of rehospitalisations in moderately and severely disabled patients with COPD.
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| 7. |
- Foghagen, Christer
(författare)
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Öländska platser : anslagstavlor i synliggörandets geografi
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is an explorative excursion into the concept of place creation and place construction. It departures from the way place is discussed within both relational theory and humanistic geography. In pace with changes in the local economy and re-structure of the agricultural sector, the Swedish island, Öland, has gone through changes which has given new perspectives on place and the distinctiveness of single places. These changes have assigned new roles for single places and the processes of place creation and place construction takes new paths in these changes.The study focuses on three major research questions:• How is place created?• How are processes of place creation manifested on Öland?• What role does the distinctiveness of particular places have for tourism and entrepreneurship on the island Öland?The approach to these questions is explorative. Place is studied as a concept which both reflects and influences processes of change in relation to other places and different actors, people and organizations. In this study, place creation is analyzed in relation to changing economic, social and cultural aspects. People’s actions in a certain place or in different places affect place transformation and creation of place just as changes in the national and global economy do. The different images people have of a certain place and their actions in this place are affected by relations to other places and cultural values, identities, global trends and the overall economy. This plays a vital role for place creation and how distinct places are constructed. This study explores these processes on Öland through three different projects or case studies. Methodologically, I have a qualitative approach to my research questions and the case studies are based on interviews, observations and analyses of marketing material, information material, texts and pictures.
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| 8. |
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| 9. |
- Gudmundsson, Gunnar, et al.
(författare)
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Mortality in COPD patients discharged from hospital : the role of treatment and co-morbidity
- 2006
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Ingår i: Respiratory Research. - : Springer Science and Business Media LLC. - 1465-9921 .- 1465-993X. ; 7, s. 109-
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Tidskriftsartikel (refereegranskat)abstract
- Background: The aim of this study was to analyse mortality and associated risk factors, with special emphasis on health status, medications and co-morbidity, in patients with chronic obstructive pulmonary disease ( COPD) that had been hospitalized for acute exacerbation.Methods: This prospective study included 416 patients from each of the five Nordic countries that were followed for 24 months. The St. George's Respiratory Questionnaire (SGRQ) was administered. Information on treatment and co-morbidity was obtained.Results: During the follow-up 122 (29.3%) of the 416 patients died. Patients with diabetes had an increased mortality rate [HR = 2.25 (1.28 - 3.95)]. Other risk factors were advanced age, low FEV1 and lower health status. Patients treated with inhaled corticosteroids and/or long-acting beta-2-agonists had a lower risk of death than patients using neither of these types of treatment.Conclusion: Mortality was high after COPD admission, with older age, decreased lung function, lower health status and diabetes the most important risk factors. Treatment with inhaled corticosteroids and long-acting bronchodilators may be associated with lower mortality in patients with COPD.
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Hallin, Christer, et al.
(författare)
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Improved Ni ohmic contact on n-type 4H-SiC
- 1997
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 26:3, s. 119-122
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the structural, chemical and electronic properties of Al/Ni/ Al-layers evaporated on 4H silicon carbide and then annealed at 1000°C for 5 min. The structure was investigated before and after annealing by transmission electron spectroscopy from cross-sectional specimens. With x-ray photoelectron spectroscopy, both element distribution and bonding energies were followed during sputtering through the alloyed metal-semiconductor contact. Voids are found in both annealed Ni/4H-SiC and Al/Ni/Al/4H-SiC contact layers, though closer to the metal-semiconductor interface in the former case. The first aluminum-layer is believed to prevent voids to be formed at the interface and also to reduce the oxide on the semiconductor surface. The contact was found to be ohmic with a specific contact resistance ρc - 1.8 × 10−5 Ωcm2 which is more than three times lower ρc than for the ordinary Ni/4H-SiC contact prepared in the same way.
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| 14. |
- Hallin, Christer, et al.
(författare)
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The effect of thermal gradients on SiC wafers
- 2003
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Ingår i: Materials Science Forum, Vols. 433-436. ; , s. 193-196
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Konferensbidrag (refereegranskat)abstract
- An in-situ curvature measurement equipment has been used to measure the curvature change of 4H-SiC 8degrees off-axis wafers, both with and without a CVD grown epitaxial layer, under beat treatments. The curvature of the wafer was found to increase while heating on the back-side and measuring on the front-side. This was independent whether Si- or C-face was towards the heater. The change in curvature was similar to0.05 m(-1) when ramping the temperature from R.T. up to 1300 degreesC, and was slightly more pronounced in the <11 (2) over bar0> direction compared with the <1 (1) over bar 00> direction.
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| 15. |
- Hallin, Runa, 1952-
(författare)
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Nutritional Depletion in Chronic Obstructive Pulmonary Disease (COPD) : Effect on Morbidity, Mortality and Physical Capacity
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of this work was to examine the effects of depleted nutritional status on some aspects of Chronic Obstructive Pulmonary Disease (COPD).Morbidity. In paper І, we found that energy intake was lower than the calculated energy demand for all patients. A low body mass index (BMI) at inclusion and weight loss, during the one year follow-up period were independent risk factors for having a new exacerbation (p = 0.003 and 0.006, respectively).Mortality. Nineteen percent of the patients in paper ІІ, where underweight (BMI<20). A significant positive correlation was found between BMI and FEV1, and this correlation remained significant after adjustment for age, sex and pack years (p<0.0001). Being underweight was related to increased overall mortality and respiratory mortality but not to mortality of other causes, 19% of the patients had died within 2 years. The lowest mortality was found among the overweight patients (BMI 25-30 kg/m).Physical capacity and effect of training. In paper ІІІ we investigated baseline characteristics of patients that were starting physical training. We found that peak working capacity was positively related to BMI (r=0.35, p=0.02) and fat free mass index (FFMI) (r=0.49, p=0.004) and negatively related to S-Fibrinogen and serum C reactive protein (S-CRP). BMI and FFMI were significantly related to the 12 minutes walking distance when adjusted for body weight. Fifty to 76% of the variation in physical capacity was accounted for when age, gender, FEV1, FFMI and CRP were combined in a multiple regression model.In Paper ІV the median change in fat free mass (FFM), after 4 months of physical training was 0.5 kg. Old age, low FEV1 and high level of dyspnoea were independent negative predictors of FFM increase after the training period.In conclusion nutritional status is an important determinant of morbidity, mortality and physical capacity in COPD. Low FEV1 and high level of dyspnea are negative predictors for increased FFM after physical training.
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| 16. |
- Hallin, Runa, et al.
(författare)
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Nutritional status and long-term mortality in hospitalised patients with chronic obstructive pulmonary disease (COPD)
- 2007
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Ingår i: Respiratory Medicine. - : Elsevier BV. - 0954-6111 .- 1532-3064. ; 101:9, s. 1954-1960
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Tidskriftsartikel (refereegranskat)abstract
- Patients with chronic obstructive pulmonary disease (COPD) often have difficulties with keeping their weight. The aim of this investigation was to study nutritional status in hospitalised Nordic COPD patients and to investigate the association between nutritional status and long-term mortality in this patient group. In a multicentre study conducted at four university hospitals (Reykjavik, Uppsala, Tampere and Copenhagen) hospitalised patients with COPD were investigated. Patient height, weight and lung function was recorded. Health status was assessed with St. George's Hospital Respiratory Questionnaire. After 2 years, mortality data was obtained from the national registers in each country. Of the 261 patients in the study 19% where underweight (BMI <20), 41% were of normal weight (BMI 20-25), 26% were overweight (BMI 25-30) and 14% were obese. FEV1 was lowest in the underweight and highest in the overweight group (p = 0.001) whereas the prevalence of diabetes and cardio-vascular co-morbidity went the opposite direction. Of the 261 patients 49 (19%) had died within 2 years. The lowest mortality was found among the overweight patients, whereas underweight was related to increased overall mortality. The association between underweight in COPD-patients, and mortality remained significant after adjusting for possible confounders such as FEV1 (hazard risk ratio (95% CI) 2.6 (1.3-5.2)). We conclude that COPD patients that are underweight at admission to hospital have a higher risk of dying within the next 2 years. Further studies are needed in order to show whether identifying and treating weight loss and depletion of fat-free mass (FFM) is a way forward in improving the prognosis for hospitalised COPD patients.
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| 17. |
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| 18. |
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| 19. |
- Hallin, Runa, et al.
(författare)
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Relation between physical capacity, nutritional status and systemic inflammation in COPD
- 2011
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Ingår i: Clinical Respiratory Journal. - 1752-6981 .- 1752-699X. ; 5:3, s. 136-142
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Tidskriftsartikel (refereegranskat)abstract
- Background: Decreased physical capacity, weight loss, fat-free mass depletion and systemic inflammation are frequently observed in patients with chronic obstructive pulmonary disease (COPD).Objective: Our aim was to examine relations between physical capacity, nutritional status, systemic inflammation and disease severity in COPD.Method: Forty nine patients with moderate to severe COPD were included in the study. Spirometry was preformed. Physical capacity was determined by a progressive symptom limited cycle ergo meter test, incremental shuttle walking test, 12-minute walk distance and hand grip strength test. Nutritional status was investigated by anthropometric measurements, (weight, height, arm and leg circumferences and skinfold thickness) and bioelectrical impedance assessment was performed. Blood samples were analyzed for C-reactive protein (CRP) and fibrinogen.Result: Working capacity was positively related to forced expiratory volume in 1 s (FEV(1)) (p < 0.001), body mass index and fat free mass index (p = 0.01) and negatively related to CRP (p = 0.02) and fibrinogen (p = 0.03). Incremental shuttle walk test was positively related to FEV(1) (p < 0.001) and negatively to CRP (p = 0.048). Hand grip strength was positively related to fat free mass index, and arm and leg circumferences. Fifty to 76% of the variation in physical capacity was accounted for when age, gender, FEV(1), fat free mass index and CRP were combined in a multiple regression model.Conclusion: Physical capacity in chronic obstructive pulmonary disease is related to lung function, body composition and systemic inflammation. A depiction of all three aspects of the disease might be important when targeting interventions in chronic obstructive pulmonary disease.
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| 20. |
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| 21. |
- Jacobson, H., et al.
(författare)
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Doping-induced strain in N-doped 4H-SiC crystals
- 2003
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 82:21, s. 3689-3691
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Tidskriftsartikel (refereegranskat)abstract
- Stress in epitaxial layers due to crystal lattice mismatch directly influences the growth, structure, and basic electrophysical parameters of epitaxial films and also to a large extent the degradation processes in semiconductor devices. In this letter, we present a theoretical model for calculating the induced lattice compression due to N doping and the critical thickness concerning formation of misfit dislocations in homoepitaxial 4H–SiC layers with different N-doping levels. For example: The model predicts that substrates with a N concentration of 3×1019 cm-3 induce misfit dislocations when the epilayer thickness reaches ∼10 μm. Also, the N-doping concentration in the 1×1018–1×1019 cm-3 range yields a strain that not will cause misfit dislocactions at the substrate and epilayer interface until an epilayer thickness of 200–300 μm is reached. Supporting evidence of the induced lattice compression due to N doping have been done by synchrotron white-beam x-ray topography on samples with different N-doping levels and are compared with the predicted results from the model
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| 22. |
- Jacobson, H, et al.
(författare)
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Doping-related strain in n-doped 4H-SiC crystals
- 2003
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Ingår i: Materials Science Forum, Vols. 433-436. ; , s. 269-272
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Konferensbidrag (refereegranskat)abstract
- Stress in epitaxial layers due to crystal lattice mismatch directly influences growth, structure, and basic electro-physical parameters of epitaxial films and also to a large extent the degradation processes in semiconductor devices. In this paper we present a theoretical model for calculating the induced lattice compression due to N doping and the critical thickness concerning formation of misfit dislocations in homoepitaxial 4H-SiC layers with different N doping levels. For example: The model predicts that substrates with N concentration of 3E19 induce misfit dislocations when the epilayer thickness reaches similar to10 mum. Also, N doping concentration in the 1E18-1E19 range yields a strain that not will cause misfit dislocactions at the substrate and epilayer interface until an epilayer thickness of 200-300 mum is reached. Supporting evidence of the induced lattice compression due to N doping have been done by synchrotron white-beam x-ray topography on samples with different N doping level and are compared with the predicted results from the model.
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| 23. |
- Jacobson, H., et al.
(författare)
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Properties and origins of different stacking faults that cause degradation in SiC PiN diodes
- 2004
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 95:3, s. 1485-1488
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Tidskriftsartikel (refereegranskat)abstract
- Different properties of the reported stacking faults (SFs) and that both these types of SF are present in the material after electrical degradation of pin diodes are shown. One is caused by perfect dislocations, deflected or misfit dislocation that had dissociated into two partial dislocations. The partials are assumed to be close to each other with a separation below the detection limit of the SWBT measurements. Thus, enough energy is provided and the leading partial moves away from the other partial and forms the extended SF.
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| 24. |
- Jacobson, Herbert, et al.
(författare)
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Properties of different stacking faults that cause degradation in SiC PiN diodes
- 2003
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Ingår i: Materials Science Forum, Vols. 433-436. ; , s. 913-916
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Konferensbidrag (refereegranskat)abstract
- The electrical degradation of 4H-SiC PiN diodes has recently attracted a large interest and is a critical material problem for high power applications. The degradation is observed as an increased forward voltage drop after forward injection operation. In this paper we present the identity, properties and origin of stacking faults with different nature that cause degradation of 4H-SiC PiN diodes.
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| 25. |
- Janson, Christer, et al.
(författare)
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Characteristics of hospitalised patients with COPD in the Nordic countries
- 2006
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Ingår i: Respiratory Medicine. - : Elsevier BV. - 0954-6111 .- 1532-3064. ; 100, s. S10-S16
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Tidskriftsartikel (refereegranskat)abstract
- The objective of the present study was to examine differences in the characteristics and management of hospitalised patients with chronic obstructive pulmonary disease (COPD) and to determine factors related to the duration of the hospital stay in the Nordic countries. The study comprised 416 patients from five University Hospitals (Bergen, Reykjavik, Uppsala, Tampere and Copenhagen). The patients were interviewed and spirometry was performed. Psychological status was assessed with the Hospital Anxiety and Depression questionnaire and quality of life with the St. Georges' Hospital Respiratory Questionnaire. The mean age was 69 years, 51% were women. The majority of the patients (76%) had severe COPD (GOLD stage III and IV) and 24% were on tong-term oxygen therapy. Forty five % of the patients had cardio-vascutar disease and 11 % diabetes. In Bergen, Uppsala and Tampere over half of the patients had anxiety and depression but the prevalence of psychiatric co-morbidity was lower in Reykjavik and Copenhagen. The median length of the hospitalisation was 7-8 days in four of the five centres but two times higher in Reykjavik. The independent predictors for a longer hospitatisation was living atone (+3 days), being on long-term oxygen (+8 days) and having diabetes (+5 days). In conclusion, this study revealed substantial differences in the characteristics and management of hospitalised COPD patients between departments of respiratory disease in five Nordic university hospitals. Living alone, concurrent diseases like diabetes and long-term oxygen therapy are predictors of more prolonged hospitalisation periods.
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| 26. |
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| 27. |
- Ji, W, et al.
(författare)
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3-D computational modeling of SiC epitaxial growth in a hot wall reactor
- 2000
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 220:4, s. 560-571
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional computational model for chemical vapor deposition (CVD) of silicon carbide (SiC) in a hot wall reactor is developed, where the susceptor is tapered with a rectangular cross-section. The present work focuses on the advection-diffusion-reaction process in the susceptor. The precursors are propane and silane, and the carrier gas is hydrogen with mass fraction higher than 98%. Computed growth rates under different system pressures and precursor concentrations are compared with the experimental data measured on samples grown in the Linkoping CVD reactor. The gas composition distribution and the growth rate profile are shown. Dependence of the growth rate on precursor concentrations is investigated.
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| 28. |
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| 29. |
- Kakanakova-Georgieva, Anelia, et al.
(författare)
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Hot-wall MOCVD grown homoepitaxial GaN layers with intense intrinsic excitonic structure
- 2005
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Ingår i: Phys. Stat. Sol. (a), Vol. 202. - : Wiley. ; , s. 739-743
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Konferensbidrag (refereegranskat)abstract
- We report on a new approach to MOCVD growth of GaN, i.e. hot-wall MOCVD, and its application to homoepitaxy on GaN substrates. The quality of the epilayers is examined by photoluminescence (PL). Homoepitaxially hot-wall MOCVD grown GaN layers show (1) intense PL free-exciton emissions relative to the intensity of the principal bound-exciton emission and (2) homogeneous cathodoluminescence emission within the terraces developed during the step-flow growth. Impurity concentrations in the material are measured by secondary ion mass spectrometry (SIMS). (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 30. |
- Kakanakova-Georgieva, A, et al.
(författare)
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Implementation of hot-wall MOCVD in the growth of high-quality GaN on SiC
- 2003
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Ingår i: Materials Science Forum, Vols. 433-436. - : Trans Tech Publications. ; , s. 991-994
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Konferensbidrag (refereegranskat)abstract
- This paper reports on the growth of high-quality GaN layers on SiC substrates by hotwall MOCVD. Use of AlN buffer with a thickness exceeding 50 nm is employed for the GaN deposition and it is found to encompass most of the misfit defects. A narrower X-ray rocking curve over asymmetric than over symmetric reflection is measured - full width at a half maximum (FWHM) of 350 arcsec vs. FWHM of 490 arcsec for 10.4 and 00.2 peaks, respectively, indicating high overall quality of the film. The free exciton photoluminescence emission peak has rather narrow FWHM of 5 meV. The typical thickness of the GaN layers is about 2 mum and they are completely depleted according to the capacitance-voltage profiling, which corresponds to estimated residual doping of less than 5x10(14) cm(-3). Only in some cases when the GaN layer is not depleted, deep level transient spectroscopy is performed and two deep traps with activation energies of 0.26 and 0.59 eV below the conduction band are measured.
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| 31. |
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| 32. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Structural properties of 6H-SiC epilayers grown by two different techniques
- 1997
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Ingår i: Materials Science and Engineering B. - 0921-5107. ; 46:1-3, s. 345-348
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we investigated the structural properties of 6H-SiC homoepitaxial layers utilizing microhardness and X-ray characterization techniques. The growth was performed by chemical vapour deposition (CVD) and liquid phase epitaxy (LPE) under various growth conditions. The depth Knoop hardness profiles represent decreasing curves due to the indentation size effect. With load increasing the curves saturate reaching microhardness values comparable with the known Vickers ones. At about 0.4 μm beneath the layer surfaces the curves show small plateaus which may be attributed to structural inhomogeneity. This is suggested by X-ray diffraction spectra taken from the same samples, which contain additional peaks besides the typical ones for 6H-SiC.
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| 33. |
- Kordina, Olle, et al.
(författare)
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Growth of SiC by "Hot-Wall" CVD and HTCVD
- 1997
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Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 202:1, s. 321-334
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Tidskriftsartikel (refereegranskat)abstract
- A reactor concept for the growth of high-quality epitaxial SiC films has been investigated. The reactor concept is based on a hot-wall type susceptor which, due to the unique design, is very power efficient. Four different susceptors are discussed in terms of quality and uniformity of the grown material. The films are grown using the silane–propane–hydrogen system on off-axis (0001) 6H- and 4H-SiC substrates. Layers with doping levels in the low 1014 cm—3 showing strong free exciton emission in the photoluminescence spectra may readily be grown reproducibly in this system. The quality of the grown layers is also confirmed by the room temperature minority carrier lifetimes in the microsecond range and the optically detected cyclotron resonance data which give mobilities in excess of 100000 cm2/Vs at 6 K. Finally, a brief description will be given of the HTCVD technique which shows promising results in terms of high quality material grown at high growth rates.
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| 34. |
- Lofgren, PM, et al.
(författare)
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3-d thermal and flow modeling of hot wall epitaxial chemical vapor deposition reactors, heated by induction
- 2000
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 338-3, s. 153-156
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Tidskriftsartikel (refereegranskat)abstract
- A three dimensional computational model for temperature and flow predictions in hot wall chemical vapor deposition (CVD) reactors, heated by induction, is presented. It includes heating by a Radio Frequency (RF) coil, flow and heat transfer. Thermal radiation is modeled by a modified Monte Carlo method. Model predictions are compared to full scale experiments at Linkoping CVD reactor for epitaxial growth of silicon carbide (SIC). Both streamwise and spanwise temperature gradients are well predicted, with the temperature maximum location shifted slightly upstream compared to the measured. Additionally, the model succeeds in predicting a recirculation zone just downstream of the susceptor. It is demonstrated how thermal gradients can be greatly reduced by simple geometrical changes.
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| 35. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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Hole effective masses in 4H SiC
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:16
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Tidskriftsartikel (refereegranskat)abstract
- Optically detected cyclotron resonance (ODCR) at X-band frequency (~9.23 GHz) was used to study hole effective masses in 4H SiC. In addition to the known ODCR signal related to the cyclotron resonance (CR) of electrons we have observed an ODCR peak at a higher magnetic field, which is attributed to the CR of holes. In the vicinity of the maximum of the uppermost valence band, the constant energy surface can be considered as an ellipsoid with the principal axis along the c axis and the effective masses of the holes were determined as mh? = (0.66▒0.02)m0 and mh?=(1.75▒0.02)m0. The influence of the polaron coupling effect on the effective mass values in 4H SiC is discussed. ⌐ 2000 The American Physical Society.
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| 36. |
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| 37. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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Optically detected magnetic resonance studies of intrinsic defects in 6H-SiC
- 1999
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Ingår i: Semiconductor Science and Technology. - 0268-1242 .- 1361-6641. ; 14:12, s. 1141-1146
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Tidskriftsartikel (refereegranskat)abstract
- Optically detected magnetic resonance (ODMR) was used for study of defects in n-type 6H-SiC. Four ODMR spectra related to spin S = 1 centres were observed. Two of these centres, labelled a and b, have a trigonal symmetry with the symmetry axis along the c-axis of the hexagonal crystal. For the other two centres, labelled c and d, the symmetry is lower (C1h) and the principal axis z of the g- and D-tensor is about 71 degrees off the c-axis. Based on the symmetry axes, the annealing behaviour and the intensity, these spectra are suggested to originate from different configurations of the paired centre between a silicon vacancy and a nearest-neighbour point defect (either a carbon vacancy or a silicon antisite), occupying different inequivalent sites in the 6H-SiC. These defects are non-radiative and act as efficient recombination channels in the material.
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| 38. |
- Nguyen, Tien Son, et al.
(författare)
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Hole and electron effective masses in 6H-SiC studied by optically detected cyclotron resonance
- 2002
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Ingår i: Materials Science Forum(ISSN 0255-5476), Vols. 389-393. - : Trans Tech Publications. ; , s. 525-528
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Konferensbidrag (refereegranskat)abstract
- We used optically detected cyclotron resonance (ODCR) at X-band frequency (similar to9.23 GHz) to study the hole effective masses in 6H-SiC. In high-purity 6H-SiC layers, two well-resolved cyclotron resonance (CR) peaks have been observed and attributed to the CR of electrons and holes. In 6H-SiC, the uppermost valence band near its maximum is found to be parabolic with the hole transverse effective mass m(hperpendicular to)=(0.66 +/- 0.02) m(0) and the longitudinal effective mass component M-hparallel to =(1.85 +/- 0.03) m(0). The average of the electron effective mass components in the basal plane-the transversal mass-is determined as m(eperpendicular to)=(0.48 0.02) m(0). With the obtained OJDCR data we can estimate the longitudinal electron effective mass to be in the range 3-6 m(0) depending on the anisotropy of the effective mass in the basal plane.
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| 39. |
- Nguyen, Tien Son, et al.
(författare)
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Hole effective masses in 6H-SiC from optically detected cyclotron resonance
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:4
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Tidskriftsartikel (refereegranskat)abstract
- We used optically detected cyclotron resonance (ODCR) at X-band frequency (similar to9.23 GHz) to study the hole effective masses in 6H-SiC. In high-purity 6H-SiC layers, two well-resolved cyclotron resonance (CR) peaks have been observed and attributed to the CR of electrons and holes. Similar to 4H-SiC, the hole effective mass in 6H polytype is also found to be isotropic in the basal plane with the transverse mass m(hperpendicular to)=(0.66+/-0.02) m(0). The hole effective mass component along the c-axis is determined as m(hparallel to)=(1.85+/-0.03) m(0). From the obtained data we can estimate the electron effective mass component along the c-axis to be in the range 3-6 m(0) depending on the anisotropy of the electron effective mass in the basal plane.
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| 40. |
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| 41. |
- Olafsson, HO, et al.
(författare)
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A comparison between SiO2/4H-SiC interface traps on (0001) and (1120) faces
- 2004
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 457-460, s. 1305-1308
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Tidskriftsartikel (refereegranskat)abstract
- We present thermally stimulated current (TSC) measurements made on metal-oxide-semiconductor (MOS) structures fabricated on off-axis (0001) or on-axis (1120) face n-type 4H-SiC with wet or dry oxides. The TSC measurements show the interface trap spectra of traps with activation energies in the range from 0.1 to 0.6 eV. Varying the charging and discharging conditions, we are able to distinguish between two types of traps which are both present on (0001) and (1120) face samples. One type is sensitive to the electric field during discharging but is insensitive to the charging temperature, while the other type is insensitive to the electric field during discharging but can not capture electrons at low temperatures. We find that, compared to the (0001) face, the traps at the (1120) face are shifted in energy about 0.1 eV towards higher activation energies. In all cases, For wet or dry oxides made on the (0001) or the (1120) face, the number density of traps is above 7x10(12) cm(-2).
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| 42. |
- Osterman, J., et al.
(författare)
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Scanning spreading resistance microscopy of aluminum implanted 4H-SiC
- 2003
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 102:1-3, s. 128-131
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Results from the application of scanning spreading resistance microscopy (SSRM) for characterization of aluminum implanted 4H-SiC are presented. The implanted profiles are investigated electrically and morphologically as a function of post-implantation anneal conditions. The method is shown to be advantageous for measuring and optimizing the activation in many aspects with respect to existing alternative techniques: it provides information of the entire depth and Al concentration range, it is unaffected by annealing induced re-growth and/or surface roughening, and requires little sample preparation. The results indicate that the apparent activation and surface roughness do not saturate in the investigated temperature range of 1500-1650 °C. Finally, an apparent activation energy for the process of 3 eV is estimated. © 2003 Elsevier B.V. All rights reserved.
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| 43. |
- Robbie, K, et al.
(författare)
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Study of contact formation by high temperature deposition of Ni on SiC
- 2000
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 338-3, s. 981-984
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Tidskriftsartikel (refereegranskat)abstract
- We report the observation, by scanning tunneling microscopy (STM), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and atomic force microscopy (AFM), of island formation on SIC during high temperature deposition and annealing of thin Ni films. Ni films with a nominal thickness of 2.5 monolayers were sputter deposited onto H-2-etched single crystal 6H-SiC (0001) substrates heated to 600 degreesC in an ultrahigh vacuum STM system. After the substrates were annealed to 800-1000 degreesC, island formation was observed by STM. The islands were 0.1-0.5 mum in diameter, similar to 30 nm high, and separated by similar to2 mum from each other, with an exceptionally flat top with a peculiar 'stitched' surface structure. A second type of island, similar to1.5 mum in diameter, similar to 10 nm high, and separated by similar to 10 mum from each other, was observed by ex situ AFM and SEM. Microspot AES showed that the first islands are composed of Ni and C, while the second islands are composed of Ni, C, and Si. AES lineshape studies showed that the carbon in both types of islands is graphitically bound as opposed to the carbon in the substrate which is carbidically bound. From comparisons to literature, we believe that the first islands are a new type of graphite intercalation compound. An indexing of Ni on the top graphite sheets is presented for each anneal temperature.
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| 44. |
- Storasta, Liutauras, et al.
(författare)
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Electrical activity of residual boron in silicon carbide
- 2002
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Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 549-552
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Konferensbidrag (refereegranskat)abstract
- Defects in high quality 4H silicon carbide epilayers have been studied using Deep Level Transient Spectroscopy (DLTS) and Minority Carrier Transient Spectroscopy (MCTS). Both intrinsic defect related centers HS1, Z(1/2). EH6/EH7 and shallow and deep boron centers were found. Electrical properties of the boron related traps are analyzed. Comparison with the optical decay measurements shows that boron is related to the observed lateral variations of the minority carrier lifetime in low doped 4H-SiC epilayers.
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| 45. |
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| 46. |
- Sveinbjornsson, EO, et al.
(författare)
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High Field Effect Mobility in Si Face 4H-SiC MOSFET Made on Sublimation Grown Epitaxial Material
- 2005
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Ingår i: Materials Science Forum, Vols. 483-485. ; , s. 841-844
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Konferensbidrag (refereegranskat)abstract
- We report on fabrication and characterization of n-channel Si face 4H-SiC MOSFETs made using sublimation grown epitaxial material. Transistors made on this material exhibit record-high peak field effect mobility of 208 cm(2)/Vs while reference transistors made on a commercial epitaxial material grown by chemical vapor deposition (CVD) show field effect mobility of 125 cm(2)/VS. The mobility enhancement is attributed to better surface morphology of the sublimation grown epitaxial layer.
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| 47. |
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| 48. |
- Sörman, E., et al.
(författare)
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Silicon vacancy related defect in 4H and 6H SiC
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:4, s. 2613-2620
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Tidskriftsartikel (refereegranskat)abstract
- We report on an irradiation-induced photoluminescence (PL) band in 4H and 6H SiC and the corresponding optically detected magnetic resonance (ODMR) signals from this band. The deep PL band has the same number of no-phonon lines as there are inequivalent sites in the respective polytype. These lines are at 1352 and 1438 meV in the case of 4H and at 1366, 1398, and 1433 meV in the case of 6H. The intensity of the PL lines is reduced after a short anneal at 750░C. ODMR measurements with above-band-gap excitation show that two spin-triplet (S=1) states with a weak axial character are detected via each PL line in these bands. One of these two triplet states can be selectively excited with the excitation energy of the corresponding PL line. These triplet signals can therefore be detected separately and only then can the well documented and characteristic hyperfine interaction of the silicon vacancy in SiC be resolved. Considering the correlation between the irradiation dose and the signal strength, the well established annealing temperature and the characteristic hyperfine pattern, we suggest that this PL band is related to the isolated silicon vacancy in 4H and 6H SiC. The spin state (S=1) implies a charge state of the vacancy with an even number of electrons. By combining the knowledge from complementary electron-spin resonance measurements and theoretical calculations we hold the neutral charge state for the strongest candidate. ⌐2000 The American Physical Society.
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| 49. |
- ul-Hassan, Jawad, 1974-, et al.
(författare)
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Properties of Thick n- and p-type Epitaxial Layers of 4H-SiC Grown by Hot-Wall CVD on off- and on-axis Substrates
- 2006
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Ingår i: Materials Science Forum, Vols. 527-529. ; , s. 183-186
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Konferensbidrag (refereegranskat)abstract
- Thick epitaxial layers of 4H-SiC both n- and p-type were grown using horizontal Hot- Wall CVD (HWCVD). No large difference in the carrier lifetime was observed for the layers grown on n- and p-type substrates. The carrier lifetime usually increases with the increasing thickness of the epilayer. To investigate if the growth conditions and material properties are changing during the longer growth time a sample was prepared with uniformly varying epilayer thickness from 20μm on one side to 110μm on other side. Results of optical and electrical measurements, the variation in background impurities and other deep levels are discussed. Furthermore, the properties of thick layers grown on on-axis substrates are presented.
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| 50. |
- Vetter, W.M., et al.
(författare)
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Dislocation loops formed during the degradation of forward-biased 4H-SiC p-n junctions
- 2003
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 98:3, s. 220-224
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Tidskriftsartikel (refereegranskat)abstract
- The partial dislocations that border triangle or parallelogram-shaped stacking faults formed during the degradation of p-n diodes fabricated on 4H-SiC wafers were determined by transmission X-ray topography to be dislocation loops of Burgers vector 1/3<101¯0>, the Shockley partial type, consistent with previously reported TEM results. Some were separated from axial screw dislocations also present in the sample, indicating that the axial dislocations were not involved in the loops' nucleation, while others were seen to have interacted during their growth with the axial screw dislocations, distorting their shapes from those of ideal parallelograms. © 2003 Elsevier Science B.V. All rights reserved.
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