| 1. |
- Carlsson, N, et al.
(författare)
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IMPROVED SIZE HOMOGENEITY OF INP-ON-GAINP STRANSKI-KRASTANOW ISLANDS BY GROWTH ON A THIN GAP INTERFACE LAYER
- 1995
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 156:1-2, s. 23-29
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Tidskriftsartikel (refereegranskat)abstract
- Coherent InP nano-sized islands, embedded into GaInP, have been grown by metal-organic vapour phase epitaxy using the Stranski-Krastanow growth mode. Photoluminescence, atomic force microscopy and transmission electron microscopy studies show that the insertion of a thin ∼ 4 monolayer thick GaP layer affects the critical thickness of the subsequently deposited two-dimensional InP wetting layer, increasing it from ∼ 1.5 monolayers (without an inserted GaP layer) to ∼ 2.5 monolayers (with an inserted GaP layer). We demonstrate that the inserted GaP layer affects also the island formation. The bimodal size distribution of Stranski-Krastanow islands, typical for low InP coverages, can be overcome without island coalescence by deposition on top of the thin GaP layer, where a coverage of InP of about 3.5–4.5 monolayers results in the formation of almost only the larger, fully developed, pyramidal islands. Annealing experiments at growth temperature of 580°C show that these islands (base area ≈ 40 × 50 nm2, height ≈ 10–15 nm, surface density ≈ (1−2) × 109 cm−2) are rather stable in a time-scale over several minutes before they slowly undergo an Ostwald ripening process.
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| 2. |
- Bertone, Daniele, et al.
(författare)
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Etching of InP-based MQW laser structure in a MOCVD reactor by chlorinated compounds
- 1998
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 195:1-4, s. 624-629
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Tidskriftsartikel (refereegranskat)abstract
- Four different chlorinated compounds: 2-chloropropane, dichloromethane, chloroform and carbon tetrachloride have been used to etch InGaAsP/InP MQW laser structures partially masked. Etching experiments were performed in a home-made LP-MOCVD reactor with argon or argon + hydrogen as carrier gas, using phosphine (PH3) or tertiarybutylphosphine (TBP) to prevent thermal decomposition. The etching temperature as well as the chlorinated compound flow were varied to obtain the best trade-off between etch rate and surface morphology. The optimized experimental conditions were applied to etch mesa stripes in a SCH-MQW laser structure, for the first time to our knowledge, followed by lateral InP : Fe regrowth in the same step. Threshold current as low as 4 mA (best value)-6 mA (typical value) and differential quantum efficiency higher than 20% for SI-BM MQW laser have been achieved.
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| 3. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Intrinsic modulation doping in InP-based structures : properties relevant to device applications
- 1999
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 201-202, s. 786-789
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Tidskriftsartikel (refereegranskat)abstract
- In this work we study device-relevant issues, such as doping efficiency and thermal stability, of recently proposed intrinsic modulation doping approach where intrinsic defects (PIn antisites) are used as a carrier source instead of impurity dopants. The InP/InGaAs heterostructure designed to resemble high electron mobility transistor (HEMT) structures, where all the layers were grown at a normal growth temperature 480°C except for the top InP layer which was grown at 265°C, was used as a prototype device. A comparison between the intrinsically doped structure with extrinsically doped HEMTs, which have an identical design except that the top InP layer was instead Si-doped and was grown at 480°C, reveals a high efficiency of the intrinsic doping. The thermal stability of the intrinsically doped HEMT is examined by annealing at temperatures 400-500°C relevant to possible processing steps needed in device fabrication. The observed severe reduction of the carrier concentration after annealing performed without phosphorous gas protection is attributed to the known instability of an InP surface at T>400°C. Thermal stability of the intrinsically doped HEMT is shown to be improved by using an InP cap layer grown at 480°C.
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| 4. |
- Dunuwila, D.D., et al.
(författare)
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ATR FTIR spectroscopy for in situ measurement of supersaturation
- 1997
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 179:1-2, s. 185-193
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Tidskriftsartikel (refereegranskat)abstract
- The current contribution establishes the technical feasibility of Attenuated Total Reflection (ATR) Fourier transform infrared (FTIR) spectroscopy for the in situ measurement of supersaturation in crystallization processes. The approach was inspired by recent advancements in ATR spectroscopy by way of various light transfer systems for remote sensing and by the increasing availability of ATR configurations well suited for remote, in situ measurements. The feasibility of the technique was investigated using a DIPPER-210® immersion probe manufactured by Axiom Analytical, Inc. Initial experiments conducted using aqueous maleic acid proved that ATR FTIR spectroscopy can be successfully employed to measure supersaturation, solubility and the metastable limit, in situ, with sufficient accuracy and precision.
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| 5. |
- LeCaptain, D.J., et al.
(författare)
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Applicability of second harmonic generation for in situ measurement of induction time of selected crystallization systems
- 1999
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 203:4, s. 564-569
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear optical technique of second harmonic generation (SHG) is introduced as a novel technique for monitoring particle formation in batch crystallizations. SHG is more sensitive and is less prone to interference than turbidometric methods. The studies presented show the applicability of SHG as a method for in situ measuring the induction time of a number of noncentrosymmetric crystal systems.
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| 6. |
- LI, G, et al.
(författare)
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ZN DELTA-DOPED GAAS GROWN BY METALORGANIC VAPOR-PHASE EPITAXY
- 1995
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 154, s. 231-239
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Tidskriftsartikel (refereegranskat)abstract
- A number of delta-doping parameters have been changed to study their effects on the hole concentration of Zn delta-doped GaAs grown by metalorganic vapour phase epitaxy using dimethylzinc (DMZn) as a doping precursor. We observed that the hole concentration is dependent on the DMZn partial pressure but independent of the gas now velocity in the reactor. A weak effect of the delta-doping time on the hole concentration infers that the near-equilibrium between the Zn adsorption and desorption can be reached very rapidly. In the regime of the delta-doping temperatures from 600 to 700 degrees C, the Zn desorption predominantly determines the hole concentration, and the Zn desorption activation energy obtained from the Arrhenius-type plot is 2.04 eV. Below 600 degrees C, however, the hole concentration departures from the Arrhenius-type relationship with the reciprocal delta-doping temperature, indicating that some other factors start to influence the Zn delta-doping concentration.
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| 7. |
- Pan, Borlan, et al.
(författare)
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Time-resolved fluorescence and anisotropy of covalently coupled 1-pyrenebutyric acid for monitoring the crystallization conditions of lysozyme
- 1997
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 171:1-2, s. 226-235
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved fluorescence and anisotropy measurements of trace amounts of 1-pyrenebutyric acid labeled hen egg-white lysozyme (PBA-HEL) were used to characterize hen egg-white lysozyme (HEL) crystallization conditions. The effects of sodium chloride and protein concentrations on the fluorescence lifetimes and rotational correlation times of the labeled protein were examined. These results were compared with the effects of the salts ammonium acetate and ammonium sulfate. Addition of protein precipitants caused increases in the rotational correlation times which were attributed to a combination of steric, hydrodynamic, general electrostatic and specific ionic interactions. This decrease in the rotational mobility of HEL appears to be a necessary but not sufficient condition to allow the formation of specific interactions leading to crystallization. The results demonstrated that fluorescence measurements are effective in characterizing and monitoring protein crystallization processes prior to the appearance of macroscopic crystals.
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| 8. |
- Schwartz, A.M., et al.
(författare)
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Use of Raman spectroscopy for in situ monitoring of lysozyme concentration during crystallization in a hanging drop
- 1999
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 203:4, s. 599-603
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Tidskriftsartikel (refereegranskat)abstract
- Fiber optic Raman spectroscopy combined with a partial least-squares regression model was investigated as a means to monitor lysozyme concentration during crystallization in a hanging drop experiment in real time. Raman spectral features of the buffer and protein were employed to build the regression model. This model was used to calculate the compositional changes within the hanging drop. The use of fibre optic technology coupled with Raman spectroscopy, which is ideal for use with aqueous media, results in a powerful noninvasive probe of the changing environment within the solution. These preliminary findings indicate that solubility as well as supersaturation measurements can be made.
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| 9. |
- Syväjärvi, Mikael, et al.
(författare)
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Growth of 6H and 4H-SiC by sublimation epitaxy
- 1999
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 197:1-2, s. 155-162
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Tidskriftsartikel (refereegranskat)abstract
- The epitaxial sublimation growth process of SiC has been investigated. Layers with specular surfaces and growth rates up to 2 mm/h have been obtained. No step bunching is observed by optical microscopy even on very thick layers which indicates a stable step growth mechanism. Under certain growth conditions the morphology degrades. The morphological stability is investigated and discussed in relation to the growth kinetics. Impurities in the epitaxial layers are investigated by secondary ion mass spectroscopy and low-temperature photoluminescence. The carrier concentration is measured by capacitance–voltage measurements. The structural quality of the grown material is improved compared to the substrate as shown by X-ray diffraction measurements.
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| 10. |
- Tuominen, M., et al.
(författare)
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Investigation of domain evolution in sublimation epitaxy of SiC
- 1998
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 193:1-2, s. 101-108
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Tidskriftsartikel (refereegranskat)abstract
- High resolution X-ray diffractometry has been applied to study domain misorientation in SiC epi-layers grown by the sublimation epitaxy method. A pronounced effect of the growth conditions on the mosaicity of the epi-layer has been observed. The results are discussed in terms of domain evolution and structural changes during the epi-growth under different growth conditions.
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