Correlation of CdZnTe(211)B substrate surface morphology and HgCdTe(211)B epilayer defects |
| |
Authors: | J Zhao Y Chang G Badano S Sivananthan J Markunas S Lewis J H Dinan P S Wijewarnasuriya Y Chen G Brill N Dhar |
| |
Affiliation: | (1) Microphysics Laboratory, University of Illinois at Chicago, 60607 Chicago, IL;(2) United States Army RDECOM CERDEC NVESD, 22060 Fort Belvoir, VA;(3) United States Army Research Laboratory, 20783 Adelphi, MD |
| |
Abstract: | We present results on the surface morphology and recombination lifetimes of molecular-beam epitaxy (MBE)-grown HgCdTe (211)B
epilayers and correlate them with the roughness of the CdZnTe substrate surfaces. The substrate surface quality was monitored
by in-situ spectroscopic ellipsometry (SE) and reflection high-energy electron diffraction (RHEED). The SE roughness of the
substrate was measured after oxide desorption in the growth chamber. The RHEED patterns collected show a strong correlation
with the SE roughness. This proves that SE is a valuable CdZnTe prescreening tool. We also found a correlation between the
substrate roughness and the epilayer morphologies. They are characterized by a high density of thin elongated defects, “needle
defects,” which appear on most samples regardless of growth conditions. The HgCdTe epilayers grown on these substrates were
characterized by temperature-dependent, photoconductive decay-lifetime data. Fits to the data indicate the presence of mid-gap
recombination centers, which were not removed by 250°C/24-h annealing under a Hg-rich atmosphere. These centers are believed
to originate from bulk defects rather than Hg vacancies. We show that Te annealing and CdTe growth on the CdZnTe substrates
smooth the surface and lower substantially the density of needle defects. Additionally, a variety of interfacial layers were
also introduced to reduce the defect density and improve the overall quality of the epilayer, even in the presence of less
than perfect substrates. Both the perfection of the substrate surface and that of its crystalline structure are essential
for the growth of high-quality material. Thus, CdZnTe surface polishing procedures and growth techniques are crucial issues. |
| |
Keywords: | Molecular beam epitaxy (MBE) HgCdTe defects surface morphology ellipsometry reflection high-energy electron diffraction (RHEED) |
本文献已被 SpringerLink 等数据库收录! |
|