Influences of two-step growth and off-angle Ge substrate on crystalline quality of GaAs buffer layers grown by MOVPE
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Author list: Wanarattikan P., Sanorpim S., Denchitcharoen S., Uesugi K., Kuboya S., Onabe K.
Publisher: Elsevier
Publication year: 2015
Journal: Journal of Crystal Growth (0022-0248)
Volume number: 414
Start page: 15
End page: 20
Number of pages: 6
ISSN: 0022-0248
eISSN: 1873-5002
Languages: English-Great Britain (EN-GB)
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Abstract
GaAs buffer layers were grown on off-angle Ge substrates with a two-step growth process by metalorganic vapor phase epitaxy in order to prepare a high quality buffer layer for the InGaAsN p-i-n solar-cell structure. In our contribution, we present results from the optimized two-step growth of GaAs buffer layers, namely with a low-temperature step at 470 C and a high-temperature step at 580 C, combined with the use of Ge substrates misoriented by 4 and 6 towards [1 1 0]. HRXRD results showed that by using the off-angle substrates, the FWHM of (0 0 4) rocking curves was decreased to 6.7 sec, which is about 4 times the FWHM of the GaAs commercial substrate. A decreased FWHM indicates a narrower distribution of crystal orientation. Furthermore, a smooth surface with a RMS roughness of 0.7 nm was clearly observed by AFM. Cross-sectional dark-field TEM images showed the GaAs buffer layer with 20-30 nm diamond-shaped anti-phase domains (APDs) at the GaAs/Ge interface, followed by APDs-free GaAs regions on the 6 off-angle Ge substrate. However, anti-phase boundaries were generated along the [0 0 1] direction for the buffer layer on the on-axis substrate. Our results demonstrated that the use of 6 off-angle Ge substrate and a two-step growth process allow the suppression of APDs in the GaAs buffer layer. ฉ 2014 Elsevier B.V. All rights reserved.
Keywords
A1. High resolution X-ray diffraction, A3. Metaloganic vapor phase epitaxy, B2. Semiconducting gallium arsenide, B2. Semiconducting germanium
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