We employ effective-mass theory for degenerate hole bands to calculate
the acceptor binding energies for Be, Mg, Zn, Ca, C, and Si substitut
ional accepters in GaN and ALN. The calculations are performed through
the 6 x 6 Rashba-Sheka-Pikus and the Luttinger-Kohn matrix Hamiltonia
ns for wurtzite (WZ) and zinc-blende (ZB) crystal phases, respectively
. An analytic representation for the acceptor pseudopotential is used
to introduce the specific nature of the impurity atoms. The energy shi
ft due to polaron effects is also considered in this approach. The ion
ization energy estimates are in very good agreement with those reporte
d experimentally in WZ GaN. The binding energies for ZB GaN accepters
are all predicted to be shallower than the corresponding impurities in
the WZ phase. The binding-energy dependence upon the crystal-field sp
litting in WZ GaN is analyzed. Ionization levels in AlN are found to h
ave similar ''shallow'' values to those in GaN, but with some importan
t differences which depend on the band structure parametrizations, esp
ecially the value of the crystal-field splitting used.