Extraction of Electron and Hole Ionization Coefficients From Metamorphically Grown InGaSb Diodes

Metamorphic pseudosubstrates of In
_0.15
Ga
_0.85
Sb are grown on p- and n-type GaSb substrates using In
_x
Ga
_1-x
Sb buffer layers compositionally graded in steps of x=0.03. Extensive material characterization was done on the metamorphic layers to determine the in-plane lattice constant, density of threading and misfit dislocations, and surface roughness by high-resolution X-ray diffraction, cross-sectional and plan-view transmission electron microscopy, and atomic force microscopy. This is followed by a regrowth of p-i-n and n-i-p device layers of In
_x
Ga
_1-x
Sb (x=0.10), lattice matched with the underlying partially relaxed metamorphic layer. Hole ( beta) and previously unreported electron (alpha) ionization coefficients, at room temperature and 90degC, respectively, were extracted from these structures. The results show that alpha > beta for In
_0.10
Ga
_0.90
Sb. A semianalytic expression was used to extract the temperature-dependent parameters for further investigations on practical avalanche photodiodes.