The effect of substrate orientation on the properties of low temperature molecular beam epitaxial GaAs

GaAs and related materials, grown by molecular beam epitaxy at 200-300 degrees C under normal, group V-rich conditions sire highly nonstoichiometric, with excess group V concentrations of up to 10(21) cm(-3), and the material properties are defect controlled. Here we report on comparative studies of low temperature growth of GaAs on (100) substrates and on (111)A, (111)B, (311)A, and (311)B surfaces. We show that material grown on both the (111) faces, under As-rich conditions, becomes polycrystalline almost immediately after commencement of growth. We attribute this to faceting of the surface creating regions of excessive As incorporation and either directly nucleating misorientated growth or producing areas of extreme localized strain resulting in the breakdown of crystallinity. Layers grown on (311)A and (311)B surfaces are of good crystalline quality but are highly nonstoichiometric in both cases, contrary to the anticipation that the (311)A surface, having fewer available forward Ga bonds than the (100) or (311)B surfaces might have a lower affinity for As incorporation. We also describe the reduction of excess As incorporation into layers grown on both (311) surfaces in the presence of Si or Be doping concentrations of 1 x 10(19) cm(-3) or greater as we previously reported for layers grown on (100) substrates. This is evidenced by the reduced lattice parameter and lower absorption in the near-band-edge infrared region due to As antisite defects, compared to undoped material. Also, little or no hopping conduction is seen in Be doped layers although they are totally compensated. A proportion of donors are active in the Si doped layers and the conduction mechanism seems to be normal band conductivity. Electrical activation of the Si donors and Be accepters can be increased, however, only after high temperature annealing. (C) 1997 American Institute of Physics.