Influence of Substrate Orientation on Be Transport during Molecular Beam Epitaxy of AlGaAs/GaAs Heterojunction Bipolar Transistors

The influence of substrate orientation on Be transport during GaAs molecular beam epitaxy is evaluated by secondary ion mass spectrometry and from the current-voltage characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBTs). The Be doping level employed is from 2×10 19 cm -3 to 9×10 19 cm -3 . The Be transport for the conventional (100) orientation increases rapidly with the increase of growth temperature ( T s ) from 530°C to 630°C. With substrate misorientation from (100) toward (111)A, however, Be transport is decreased at T s =630°C, and reaches a minimum with (311)A orientation. The maximum current gain of AlGaAs/GaAs HBTs grown at T s =560°C is 264 for (411)A orientation and 3 for (100) orientation, which confirms the applicability of substrate orientations other than the conventional (100) one for obtaining a sharp Be profile.