武部敏彦
GaAs(111)Aパターン基板上でのGaAs/AlGaAs
多層膜の分子線エピタクシー中のファセット成長
Abstract:Extra facet generation during molecular beam epitaxy of GaAs/AlGaAs multilayers on exact (111)A GaAs substrates patterned with ridge-type triangles with (001)-related, (110)-related, and (201)-related sidewalls, designated as "(001) triangle", "(110) triangle", and "(201) triangle", respectively, has been investigated for the first time. Extra (113)A, (001), and (114)A facets have been confirmed to generate on the (001)-related sidewalls, extra (111)B, (110), and (113)A facets on the (110)-related sidewalls, and extra (101),(238), (125), and (159) facets on the (201)-related sidewalls, depending on the intersection angle θ of the sidewall and the substrate plane. Of these, the (114)A, (110), and (159) facets were important because they persisted over a wide range of θ and, therefore, played a detrimental role in forming flat and uniform sidewall layers on the (111)A patterned substrates. The (110) and (NNM)A (N=2, 3, --;M≦N-1) facets developed on the corners of the (001) and (201) triangles, while no extra facets developed on the corners of the (110) triangles. It has been made clear that flat and uniform layers maintaining the initial as-etched triangle patterns can be grown without generating any extra facets on the sidewalls or corners for the (001) triangles with 33°≧θ≧29°, the (110) triangles with 30°≧θ≧16°, and the (201) triangles with 33°≧θ≧26°. Asymmetric growth proceeded on the triangle patterns and violated the above criteria when misoriented (111)A substrates were used. Generation of pyramidal microstructures on exact (111)A substrates and step structures on misoriented (111)A substrates during MBE growth, both composed of equivalent (110)-related facets, has been suggested to be closely related to the preferential generation of the (110) and (NNM)A facets found in the present study.