Competition of deep and shallow impurities in wide-gap II-VI semiconductors under pressure

The effects of applied pressure on deep defects, shallow ↔ deep competition, and related doping problems in II-VI semiconductors are reviewed. Photoluminescence studies to 100 kbar (at 7 K) on high purity ZnSe, and on several ZnSe samples doped with 10¹⁶ to 10¹⁹ cm^-3 Cl, Ga, N, P, and As reveal striking differences between the pressure-shifts of broad-band features involving acceptor and/or donor deep states, and excitonic lines due to shallow band-edge states. The binding energies of observed deep acceptor states tend to decrease with pressure, suggesting that compression acts to destabilize these states against competing shallow hole levels. A deep donor level assigned to an excited state of donor-vacancy_Zn complexes emerges from the electron continuum in n-type Ga-and Cl-doped samples at ≈ 25 to 28 kbar. This reviously unknown state should not affect doping in ZnSe_1-xTe_x alloys since it arises from existing compensation centers.