Formation of Defects in MBE Re-Grown GaAs Films on GaAs/AlGaAs Heterostructures
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M6.4.1
Formation of Defects in MBE Re-Grown GaAs Films on GaAs/AlGaAs Heterostructures M. Lamberti, V. Tokranov, R. Moore, M. Yakimov, A. Katsnelson, and S. Oktyabrsky School of NanoSciences and NanoEngineering, University at Albany – SUNY Albany, NY 12203, U.S.A. ABSTRACT In the present work, we examine the formation of defects on the sidewall slope in 1 µm - thick GaAs layers regrown on GaAs/AlGaAs heterostructures. Site-specific TEM specimens of sidewall slopes are obtained using focused ion beam combined with lift-out method. TEM analysis shows planar defects, such as stacking faults and microtwins, dislocations and large twinned areas, nucleating on the AlGaAs surfaces. SIMS and EDX reveal an increase in carbon and oxygen at the interface. The defect density increased with Al content exceeding 1010 cm-2 on Al0.4Ga0.6As. The defect formation is related to the oxidation of Al-containing surfaces.
INTRODUCTION Epitaxial regrowth of III-V semiconductors on patterned heterostructures provides a means to fabricate complex three-dimensional structures in various electronic and photonic applications. Quality of epitaxial film is known to be extremely sensitive to the surface morphology and contaminations. The commercially available "epi-ready" substrates allow the growth of virtually defect-free films, though still require relatively thick (>200 nm) buffer layers to bury the defects formed on the substrate surface. There are three broad problems associated with regrowth procedures: contaminations due to photolithography and wet processing; re-growth on AlGaAs; and re-growth on sidewalls. During device processing a wafer will undergo a photolithography process, with the use of photo-resist and various organic chemistries. For some devices, such as a high-brightness planar LED or laser diodes, processing technique may require regrowth of an epitaxial layer after a photolithographic step. When wet-etching is involved, in addition to photo-resist, the surface will be contaminated chemistry residues. The presence of Si, C and O as the primary contaminants is well documented [1]. There are two general approaches to epitaxial regrowth on a patterned structure documented in the literature: in-situ and ex-situ. In-situ techniques using focused ion beam, electron cyclotron resonance plasma, and Cl2 etching have been previously reported by other groups [2-4]. A study comparing an in-situ dry etch with an ex-situ wet-etch found that although the in-situ was better the ISD was of the same order of magnitude [5]. Wet-etching has been used with sulfide treatments for both re-growth and electronic passivation studies [6,7]. Another study used an in-situ STM approach to study the film surface in the etching solution itself [8]. Most of the studies investigated the planar areas of the regrown interfaces, paying little attention to the sidewalls.
M6.4.2
In this paper, we report on the studies of defect formation in MBE-regrown GaAs films on patterned GaAs/AlGaAs heterostructures with an emphasis on sidewall regrowth using ex-situ we
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