V. Iota et Ba. Weinstein, Pitfalls of using pressure to assign the luminescence of large-lattice-relaxation defects, PHYS ST S-B, 211(1), 1999, pp. 91-104
Deep defects are often assumed to be insensitive to applied pressure becaus
e of their localized character. However, in recent photoluminescence (PL) e
xperiments, several deep acceptor bands in ZnSe were found to shift with pr
essure substantially faster than the ZnSe bandgap. This shows that the opti
cal (viz., PL) levels of these accepters become more shallow under compress
ion, a result that, if also true for the thermal defect levels, is importan
t for p-type doping problems in II-VI semiconductors. We report investigati
ons of the C-3v-relaxed isolated Zn-vacancy (V-Zn) in ZnSe that help to res
olve these issues. High-pressure PL and PL-excitation (PLE) experiments and
calculations are performed on this system. We find that the V-Zn-related P
L and PLE bands have pressure coefficients that are, respectively, larger a
nd smaller than that of the ZnSe bandgap. Hence, the Stokes-shift decreases
with pressure. These results can not be understood without taking explicit
account of lattice relaxation. We employ a defect-molecule model with atom
ic wavefunctions to calculate semi-empirical configuration-coordinate diagr
ams for the V-Zn defect as a function of pressure. We find that compression
increases the Jahn-Teller coupling, but not sufficiently to overcome latti
ce stiffening. Overall, the V-Zn thermal level deepens, inhibiting p-type d
oping.