Phonon studies of Ni²⁺in GaAs:evidence for an orthorhombic Jahn-Teller system

Abstract

Thermal conductivity measurements have been made from 50 mK to 100 K of Ni-doped GaAs samples containing different proportions of Ni+, Ni2+ and Ni3+. Resonant phonon scattering at 300 GHz is assigned to Ni2+ (3T1) and this is supported by studies of photoinduced changes in the Ni2+ concentration. The scattering is attributed to tunnelling within the ground state of an orthorhombic Jahn-Teller system. Uniaxial stress measurements show that the levels are very sensitive to both E and T2 strains and provide values of VEb and VTb. Data for Cr3+(4T1) in GaAs, GaP and InP are re-examined in the light of these results. It is proposed that the rich spectrum of resonance frequencies is due to multiple-ion effects caused by ion-ion coupling via the strain field.

Thermal conductivity of isotopically enriched71GaAs crystal

“…It was intentionally undoped bulk crystal with ρ = 4.1 × 10 8 cm and µ = 5050 cm 2 V −1 s −1 at room temperature. It is worth noting that at low temperatures some impurities cause much stronger phonon scattering in GaAs than one can expect from the mass difference of the impurity only, for example, Zn, Cd [13], Cr [14,15], Ni [16]. This impurity scattering (of a resonance type in many cases) does not sizably affect the thermal conductivity value at temperatures above 100 K.…”