However, an acceptor ionization energy of 197-227 meV has been reported for Sb-doped ZnO grown by MBE .
Their calculations were consistent with experimental findings that the ionization energy for [N.sub.Se] is 100 meV .
For the film that did invert to p-type conduction, the acceptor ionization energy was estimated to be 100 meV which is the lowest reported to date (see Table 2) and seems low for the N incorporation suggested by a hole carrier density of only 1.5 x [10.sup.16] [cm.sup.-3].
Their low temperature (4 K) PL reported the acceptor-bound exciton (A0X) associated with [N.sub.O] at 3.315 eV, and the acceptor ionization energy was estimated to be 0.17-0.20 eV .
Assuming a shallow (52meV) donor is participating in the DAP transitions, the ionization energy (160 meV) suggests this N-related acceptor is also a complex defect.
As a consequence, the electrons transit from the impurity band which lowers the ionization energy, and the p-conduction arises from the [P.sub.Zn]-4[N.sub.O] acceptor complex.
The acceptor ionization energy assigned (using the method described by Wang and Giles ) to the [V.sub.Zn]-[N.sub.O]-[H.sup.+] complex is 134 meV, which is sufficiently low to allow appreciable room temperature hole conduction as we reported.
The ionization energy of an acceptor with respect to VBM is calculated as follows [1,17]:
The calculated acceptor ionization energy and formation energy of codoping with N and III elements in ZnS are presented in Table 1.
The ionization energy of single NS can be lowered by introducing the [III.sub.Zn]-[N.sub.S] passivation system due to the acceptor transition between the N level and the IBM rather than the VBM.
TABLE 1: Ionization energy [epsilon](0/-) and formation energy [DELTA][H.sub.f] of lefect complexes in ZnS.