Analysis of dark current dependent upon threading dislocations in Ge/Si heterojunction photodetectors

Abstract

PurposeThe purpose of this paper is to investigate the dependence of dark current on threading dislocations (TDs) in relaxed Ge layer for Ge/Si heterojunction photodetectors.Design/methodology/approachThe analysis of the effects of TDs is based on SRH generation and recombination mechanism used in two‐dimensional drift‐diffusion numerical simulation.FindingsIt is found that the TDs in Ge layer acting as the recombination centers lead to large dark current densities of devices, and the recombination rate is affected by the impurity out‐diffusion from Si substrate. Besides, the TDs, being the acceptor‐like defects simultaneously, form band barrier at Si/Ge interface with lightly doped Si substrates, thus limiting the minority carrier transport and resulting in low dark current densities.Originality/valueThe simulation results are excellently consistent with the experimental data and indicate that the reduction of threading dislocation densities (TDDs), especially in Ge buffer layer, dramatically decreases dark currents densities of Ge/Si photodetectors. The investigation can be applied to imbue devices with desired characteristics.