| 1. |
- Riedel, Gernot J, et al.
(författare)
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Reducing Thermal Resistance of AlGaN/GaN Electronic Devices Using Novel Nucleation Layers
- 2009
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 30:2, s. 103-106
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Tidskriftsartikel (refereegranskat)abstract
- Currently, up to 50% of the channel temperature in AlGaN/GaN electronic devices is due to the thermal-boundary resistance (TBR) associated with the nucleation layer (NL) needed between GaN and SiC substrates for high-quality heteroepitaxy. Using 3-D time-resolved Raman thermography, it is shown that modifying the NL used for GaN on SiC epitaxy from the metal-organic chemical vapor deposition (MOCVD)-grown standard AIN-NL to a hot-wall MOCVD-grown AIN-NL reduces NL TBR by 25%, resulting in similar to 10% reduction of the operating temperature of AlGaN/GaN HEMTs. Considering the exponential relationship between device lifetime and temperature, lower TBR NLs open new opportunities for improving the reliability of AlGaN/GaN devices.
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| 2. |
- J T Simms, R J T, et al.
(författare)
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Micro-Raman spectroscopy as a voltage probe in AlGaN/GaN heterostructure devices: Determination of buffer resistances
- 2011
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Ingår i: SOLID-STATE ELECTRONICS. - : Elsevier Science B.V., Amsterdam.. - 0038-1101. ; 55:1, s. 5-7
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Tidskriftsartikel (refereegranskat)abstract
- A time-resolved micro-Raman technique was developed to probe the transient voltage in the GaN buffer layer of AlGaN/GaN heterostructure devices. The transient potential distribution under Ohmic contacts of devices behaved like a capacitance-resistance coupled network, with a decrease in amplitude and phase shift of the potential as a function of operating voltage frequency. This phenomenon was used to extract a value of 0.6 M Omega/square for sheet resistance of the AIN nucleation layer at the GaN/SiC interface from the characteristic RC value of the network. This demonstrates the effectiveness of this voltage probe technique as a non-invasive method of characterizing nucleation layers.
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| 3. |
- Löwenberg, Bob, et al.
(författare)
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Addition of lenalidomide to intensive treatment in younger and middle-aged adults with newly diagnosed AML : the HOVON-SAKK-132 trial
- 2021
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Ingår i: Blood Advances. - : American Society of Hematology. - 2473-9529 .- 2473-9537. ; 5:4, s. 1110-1121
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Tidskriftsartikel (refereegranskat)abstract
- Lenalidomide, an antineoplastic and immunomodulatory drug, has therapeutic activity in acute myeloid leukemia (AML), but definitive studies about its therapeutic utility have been lacking. In a phase 3 study, we compared 2 induction regimens in newly diagnosed patients age 18 to 65 years with AML: idarubicine-cytarabine (cycle 1) and daunorubicin and intermediate-dose cytarabine (cycle 2) without or with lenalidomide (15 mg orally on days 1-21). One final consolidation cycle of chemotherapy or autologous stem cell transplantation (auto-SCT) or allogeneic SCT (allo-SCT) was provided according to a prognostic risk and minimal residual disease (MRD)-adapted approach. Event-free survival (EFS; primary end point) and other clinical end points were assessed. A second random assignment in patients in complete response or in complete response with incomplete hematologic recovery after cycle 3 or auto-SCT involved 6 cycles of maintenance with lenalidomide (10 mg on days 1-21) or observation. In all, 392 patients were randomly assigned to the control group, and 388 patients were randomly assigned to lenalidomide induction. At a median follow-up of 41 months, the study revealed no differences in outcome between the treatments (EFS, 44% +/- 2% standard error and overall survival, 54% = 2% at 4 years for both arms) although in an exploratory post hoc analysis, a lenalidomide benefit was suggested in SRSF2-mutant AML. In relation to the previous Dutch-Belgian Hemato-Oncology Cooperative Group and Swiss Group for Clinical Cancer Research (HOVON-SAKK) studies that used a similar 3-cycle regimen but did not pursue an MRD-guided approach, these survival estimates compare markedly more favorably. MRD status after cycle 2 lost prognostic value in intermediate-risk AML in the risk-adjusted treatment context. Maintenance with lenalidomide showed no apparent effect on relapse probability in 88 patients randomly assigned for this part of the study.
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| 4. |
- Mikulla, Michael, et al.
(författare)
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Manga : Manufacturable GaN
- 2011
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Ingår i: Proceedings of the 6th European Microwave Integrated Circuits Conference. - : IEEE. - 9782874870231 ; , s. 336-339
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Konferensbidrag (refereegranskat)abstract
- Manga is a five Nation (Germany, France, Italy, Sweden and United Kingdom) joint project realized by the European Defence Agency (EDA) which focuses on SiC substrates and a GaN epi wafers supply chain. The main objective of the project, started in March 2010, is to sustain the industrial development of semi-insulating silicon carbide substrates (SI SiC) and prove the industrial capability of Europe to deliver GaN HEMT and MMIC foundries with state-of-the-art GaN HEMT epitaxial wafers on SI-SiC substrates. This paper gives an overview on the current status of the technical developments achieved within the project.
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| 5. |
- Pooth, A., et al.
(författare)
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Morphological and electrical comparison of Ti and Ta based ohmic contacts for AlGaN/GaN-on-SiC HFETs
- 2017
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Ingår i: Microelectronics and Reliability. - : Elsevier BV. - 0026-2714. ; 68, s. 2-4
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Tidskriftsartikel (refereegranskat)abstract
- The morphology and impact on leakage currents of two different ohmic metal stacks for GaN based transistor devices is investigated in this work. The results have implications for the performance and reliability of a GaN transistor device. A low temperature Ta based and a higher temperature anneal Ti based metallization are compared. The low temperature process shows a smoother metal semiconductor interface together with several orders of magnitude lower vertical and lateral leakage compared to the conventional higher temperature process. In addition to the leakage tests, back bias ramping experiments are performed unveiling potential advantages of the conventional approach in mitigating current collapse. However the low leakage will enable higher voltage operation making the low temperature process the preferable choice for high power RF applications, if simultaneously current collapse can be controlled.
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| 6. |
- Tran, Dat, 1993-
(författare)
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Thermal conductivity of wide and ultra-wide bandgap semiconductors
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This PhD thesis presents experimental and theoretical studies of the thermal conductivity of wide and ultra-wide bandgap semiconductors including GaN, AlN, β-Ga2O3 binary compounds, and AlxGa1−xN, ScxAl1−xN, YxAl1−xN ternary alloys. Thermal conductivity measurements are conducted using the transient thermoreflectance (TTR) technique and the results are interpreted using analytical models based on the solution of the Boltzmann transport equation (BTE) within the relaxation time approximation (RTA). The study is motivated by the increasing research interest in these material systems due to their potential for the development of high-power (HP) and high-frequency (HF) electronic devices. Due to its wide bandgap, high electrical field, and high electronic saturation velocity, GaN is an excellent material for fast-switching HP electronic devices. AlxGa1−xN is considered a natural choice for next-generation HP electronic devices since by tuning the bandgap from 3.4 eV to 6 eV a significant increase of the critical electric field and thus the device breakdown voltage, can be achieved. Furthermore, both n- and p-type conductivity can be realized in AlGaN allowing flexible device design. β-Ga2O3 is also promising for HP electronics because of its ultra-wide bandgap (4.8 eV) and a very high Baliga’s figure of merit (FOM) exceeding by far that of GaN. Moreover, the mature growth techniques of bulk β-Ga2O3 can enable low-cost substrates with high crystal quality. ScxAl1−xN and YxAl1−xN have recently emerged as a new class of III-nitride semiconductors. Due to the large piezoelectric coefficients and spontaneous polarization in these alloys, a very large density of two-dimensional electron gas (2DEG) can be achieved at (Sc,Y)xAl1−xN/GaN heterostructures enabling high mobility transistors (HEMTs) with an enhanced HF performance as compared with the common AlxGa1−xN/GaN HEMTs. For any HP and HF device, the thermal conductivity of the constituent materials in the device structures is of crucial importance. Such devices operate at high currents, high voltages, and/or high frequencies, so a high Joule heat is generated in the device’s active region. This heat must be effectively dissipated in order to ensure high device performance and reliability. Therefore, understanding the materials’ thermal conductivity is essential for the device’s thermal management. We have investigated different bulk materials and epitaxial layers and have established the effects of dislocation density, doping, alloying, layer thickness, and crystal orientation on thermal conductivity. The results presented in this Ph.D. thesis give new insights into the thermal properties of wide and ultra-wide semiconductors and could be useful for the design, optimization, and thermal management of electronic devices based on these materials. The main research results presented in this Ph.D. thesis are summarized in six scientific papers. Paper I is focused on studying the thermal conductivity of high Al-content AlxGa1−xN and β-Ga2O3 thin layers. For β-Ga2O3 layers the effect of Sn doping on their thermal conductivity is also studied. The experimental measurements are performed in a temperature range of 280-350 K. A modified Callaway’s model is employed for the interpretation of the results. Calculations of the thickness-dependent thermal conductivity reveal quite different transport mechanisms of the two materials. Paper II presents experimental results of the thermal conductivity of thick AlxGa1−xN layers. A detailed discussion of the phonon-alloy scattering which is the main mechanism limiting the thermal conductivity of AlxGa1−xN is presented. Analyzing the interplay between the phonon-alloy scattering and the phonon-boundary scattering the experimentally observed thickness dependence of the thermal conductivity is explained. Paper III is devoted to studying the role of defects on the thermal conductivity of AlxGa1−xN alloys with 0 ≤ x ≤ 1. The effect of dislocations, impurities, free carriers, and alloying have been separately studied and discussed. The thermal conductivity of samples with various concentrations of the defect is measured and the results are interpreted using a theoretical model based on the solution of the BTE equation within the RTA. Paper IV focuses on the thermal conductivity study of ScxAl1−xN and YxAl1−xN alloys. The experimental measurements are performed for layers having compositions in the range of 0 ≤ x ≤ 0.22. The effect of phonon-alloy scattering in these alloy materials is discussed and compared with other phonon scattering processes. The experimental results are interpreted within the frame of a modified Callaway’s model in combination with ab-initio calculation for phonon dispersions and mode Grüneisen parameters. Paper V investigates the thermal conductivity anisotropy of bulk GaN. The thermal conductivity along the c- and m-axis crystallographic directions of wurtzite GaN is measured in a temperature range of 80-400 K. Experimental observations are elaborated by an analysis of the anisotropy of the phonon group velocity, the Debye temperature and the mode Grüneisen parameters. Paper VI explores the effects of doping and free carriers on the thermal conductivity of bulk GaN and homoepitaxial layers and heteroepitaxial GaN layers via both experimental and theoretical approaches. The impurities considered include Si, O, Mg, and Fe. The experimental results are analyzed using a non-Debye RTA model in combination with ab-initio calculations of the phonon dispersion.
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