Phonon scattering studies of Ni and V centres in GaP and InP

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Abstract
Thermal conductivity measurements have been made from 50 mK to 100 K of GaP and InP samples doped with Ni or V. The GaP samples both show strong resonant phonon scattering at 500 and 380 GHz respectively which is attributed to the T1-T2 tunnelling splitting associated with a dynamic orthorhombic Jahn-Teller distortion of the T1 orbital ground state of Ni2+ and V2+. Low-frequency scattering in both systems is tentatively attributed to these same ions in complex with a defect. The assignment of the scattering to V2+ is supported by studies of photo-induced changes in the V2+ concentration. Uniaxial stress measurements on GaP:V suggest strong coupling to E modes but the strength of the coupling to T2 modes is less clear. The absence of resonance scattering in a n-type sample of InP:Ni suggests the Ni is all in the Ni+ state (2T2) as expected and the absence of scattering in n-type InP:V is consistent with the instability of V2+ in that system.

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