Ge auto-doping and out-diffusion in InGaP grown on Ge substrate and their effects on the ordering of InGaP

Abstract

We report on the Ge auto-doping and out-diffusion in InGaP epilayer with Cu-Pt ordering grown on 4-in. Ge substrate. Ge profiles determined from secondary ion mass spectrometry indicate that the Ge out-diffusion depth is within 100 nm. However, the edge of the wafer suffers from stronger Ge gas-phase auto-doping than the center, leading to ordering deterioration in the InGaP epilayer. In the edge, we observed a residual Cu-Pt ordering layer left beneath the surface, suggesting that the ordering deterioration takes place after the deposition rather than during the deposition and In/Ga inter-diffusion enhanced by Ge vapor-phase auto-doping is responsible for the deterioration. We thus propose a di-vacancy diffusion model, in which the amphoteric Ge increases the di-vacancy density, resulting in a Ge density dependent diffusion. In the model, the In/Ga inter-diffusion and Ge out-diffusion are realized by the random hopping of In/Ga host atoms and Ge atoms to di-vacancies, respectively. Simulation based on this model well fits the Ge out-diffusion profiles, suggesting its validity. By comparing the Ge diffusion coefficient obtained from the fitting and the characteristic time constant of ordering deterioration estimated from the residual ordering layer, we found that the hopping rates of Ge and the host atoms are in the same order of magnitude, indicating that di-vacancies are bound in the vicinity of Ge atoms.