High carrier lifetimes in epitaxial germanium–tin/Al(In)As heterostructures with variable tin compositions

Abstract

Group IV-based germanium–tin (Ge_1−ySn_y) compositional materials have recently shown great promise for infrared detection, light emission and ultra-low power transistors. High carrier lifetimes are desirable for enhancing the detection limit and efficiency of photodetectors, low threshold current density in lasers, and low tunneling barrier height by lowering defects and dislocations at the heterointerface of a source and a channel. Here, carrier lifetimes in epitaxial germanium (Ge) and variable tin (Sn) compositional Ge_1−ySn_y materials were experimentally determined on GaAs substrates using the contactless microwave photoconductive decay (μ-PCD) technique at an excitation wavelength of 1500 nm. Sharp (2 × 2) reflection high energy electron diffraction patterns and low surface roughness were observed from the surface of the Ge_0.97Sn_0.03 epilayer. X-ray rocking curves from Ge_0.97Sn_0.03 and Ge_0.94Sn_0.06 layers demonstrated the pseudomorphic and lattice-matched growth on AlAs and In_0.12Al_0.88As buffers, respectively, further substantiated by reciprocal space maps and abrupt heterointerfaces evident from the presence of Pendellösung oscillations. High effective carrier lifetimes of 150 ns to 450 ns were measured for Ge_1−ySn_y epilayers as a function of Sn composition, surface roughness, growth temperature, and layer thickness. The observed increase in the carrier lifetime with an increasing Ge layer thickness and a reducing surface roughness, by incorporating Sn, were explained. The enhancement of the carrier lifetime with an increasing Sn concentration was achieved by controlling the defects with lattice-matched Ge_0.94Sn_0.06/In_0.12Al_0.88As heterointerfaces or the pseudomorphic growth of Ge_0.94Sn_0.06 on GaAs. Therefore, our monolithic integration of variable Sn alloy compositional Ge_1−ySn_y materials with high carrier lifetimes opens avenues to realize electronic and optoelectronic devices.