| 1. |
- Gogova, D., et al.
(författare)
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Optical and structural studies of high-quality bulk-like GaN grown by HVPE on a MOVPE AlN buffer layer
- 2006
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 21:5, s. 702-708
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Tidskriftsartikel (refereegranskat)abstract
- High-quality 400 ?m thick GaN has been grown by hydride vapour phase epitaxy (HVPE) on (0 0 0 1) sapphire with a 2 ?m thick AlN buffer layer. The material's crystalline quality and homogeneity was verified by x-ray diffraction (XRD), low-temperature photoluminesence (LT-PL) and LT cathodoluminescence. Plan-view transmission electron microscopy images reveal a low dislocation density of ~1.25 × 107 cm-2. The residual stress of the material was studied by two complementary techniques. LT-PL spectra show the main neutral donor bound exciton line at 3.4720 eV. This line position suggests virtually strain-free material with a high crystalline quality as indicated by the small full width at half maximum value of 0.78 meV. The presence of well resolved A- and B-free excitons in the LT-PL spectra and the absence of a yellow luminescence band prove the high quality of the HVPE-GaN in terms of purity and crystallinity. These findings are consistent with the XRD results, implying the high crystalline quality of the material grown. Hence, the material studied is well suited as a lattice parameter and thermal-expansion- coefficient matched substrate for further homoepitaxy, as needed for high-quality III-nitride device applications. Strain-free homoepitaxy on native substrates is needed to decrease considerably the defect density and in that way an improvement of the device's performance and lifetime can be achieved. © 2006 IOP Publishing Ltd.
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| 2. |
- Malinauskas, T, et al.
(författare)
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Contribution of dislocations to carrier recombination and transport in highly excited ELO and HYPE GaN layers
- 2006
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1426-1430
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Tidskriftsartikel (refereegranskat)abstract
- Nonequilibrium carrier dynamics has been investigated in ELO and HYPE grown GaN layers in a wide temperature and excitation range by using the time-resolved picosecond FWM technique. Carrier lifetime in the samples at 300 K increased up to 2.8-5.1 ns in accordance with the decreasing threading dislocation density from 4 x 10(7) cm(-2) (ELO) to mid 106 cm(-2) in HYPE layers. At T < 100 K, the hyperbolic shape of FWM kinetics indicated carrier density dependent radiative lifetimes, which gradually decreased at lower temperatures to a few hundreds of ps. The dominance of bimolecular recombination in HVPE layers at 10-40 K was demonstrated by the exposure characteristic of FWM, that has shown a sublinear growth of carrier density with excitation, N proportional to I-1/2. Numerical fitting of the set of FWM kinetics at various T confirmed the temperature dependence of bimolecular recombination coefficient B proportional to T-1/5 and provided its value B = 2 x 10(-11) cm(3)/s at 300 K and 3.2 x 10(-9) cm(3)/s at 9 K. The measured bipolar diffusion coefficients allowed determination of carrier diffusion length of 0.8-1 mu m at 300 K and its dependence on dislocation density and temperature. (c) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 3. |
- Monemar, Bo, et al.
(författare)
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Time-resolved spectroscopy of excitons bound at shallow neutral donors in HVPE GaN
- 2006
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 376, s. 482-485
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved photo luminescence (TRPL) data for temperatures 2-150 K are presented for two thick HVPE samples grown in two different laboratories. The samples both have residual O and Si shallow donor concentrations in the 10(16)cm(-3) range. The radiative decay time for neutral donor-bound excitons (DBEs) related to these donors is found to be about 300 ps. The decay of the DBEs at longer decay times is found to be related to feeding from the free exciton-polariton states. At elevated temperatures the decay of the DBE is very similar to the free exciton decay. (c) 2006 Elsevier B.V. All rights reserved.
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