Photoluminescence was measured at 7K in n-type material, that was doped with Ga and Cl, under pressures of up to 100kbar. For each dopant, the rate of pressure shift of the self-activated band at 25 to 30kbar changed from faster than, to slower than, that of the band gap. The change indicated that a previously unknown deep donor-like state emerged from the electron continuum. It was suggested that this state was related to Zn-vacancy plus donor complexes whose levels moved lower in the gap during compression.

T.M.Ritter, B.A.Weinstein, R.M.Park, M.C.Tamargo: Physical Review Letters, 1996, 76[6], 964-7