Amphoteric behavior and precipitation of Ge dopants in InP

Abstract

We have directly correlated the electrical behavior, the impurity lattice site location, ion damage, and the local bonding environments of Ge-dopant ions implanted into InP. We have found that after rapid thermal annealing the free electron concentration in the samples implanted at room temperature (RT) are always higher than those implanted at liquid nitrogen temperature (LNT). Although the macroscopic structure seems to be insensitive to the implantation temperature, significantly more local disorder is created in the LNT implanted amorphous layers. Moreover, the amphoteric bonding structure of the Ge atoms is found to be well established already in the as-implanted amorphous InP. After high temperature annealing (≳800 °C), the Ge atoms rearrange locally with more of the Ge substituting the In site than the P site resulting in n-type conductivity. The solid solubility of Ge in the InP is measured to be ∼1.4–1.6×1020/cm3 while the free electron concentration is estimated to saturate at ∼3.4×1019/cm3. The relatively low electron concentration can be explained by Ge precipitation and the compensation of GeIn donors by GeP acceptors in the RT implanted case. The further reduction in electron concentration in the LNT implanted samples is believed to be related to the high residual damage found in these samples. The high solubility of Ge in InP can be attributed to the availability of two possible sublattice sites for the dopant and the compensation of the local strains due to the amphoteric substitution of the Ge. The concentration ratio of the GeIn to GeP determined in the heavily implanted material has been used to estimate the difference in the formation energy of Ge substituting those two different sites.