Electrical and interfacial properties of GaAs/GaSb metal-organic vapour phase epitaxy heterostructures

The electrical properties of GaAs/GaSb heterojunctions grown by metal-organic vapour phase epitaxy were carefully investigated. The structures were formed by heavily p(Zn)-doped GaAs layers deposited on n(Te)-doped GaSb bulk crystal used as substrates. The current-voltage characteristics showed the formation of a GaSb p-n homojunction, which was expected to be induced by Zn diffusion into GaSb. Nevertheless, secondary ion mass spectrometry pointed out a small penetration depth of Zn atoms in the GaSb substrate, resulting unaffected by post-growth annealing processes. Electron beam induced current analysis demonstrated that the p-n junction interface was located more deeply into the substrate (1 lm). This result was confirmed by capacitance-voltage (C-V) and electrochemical C-V characterizations. Admittance spectroscopy led to attribute the change of conduction type from n to p in GaSb to the formation of additional shallow acceptor levels, activated by GaAs growth and post-growth thermal annealing processes. An attempt to explain the formation of the buried junction in terms of atomic interdiffusion is provided, in order to justify, from the microscopic point of view, the low diffusivity of Zn in GaSb, and the apparently uncorrelated depth of the p-n junction interface in the substrate.