Native vacancies in nitrogen-doped and undoped ZnSe layers studied by positron annihilation

We have used a low-energy positron beam to investigate the defects in N-dop ed and undoped ZnSe layers grown on GaAs:Si or ZnSe substrates. In N-doped ZnSe we observe positron trapping at vacancies, identified as VSeNSe comple xes, and at negative ions. Based on positron data, we give estimates for th e concentrations of vacancies and negative ions. The results suggest that i n addition to forming isolated Ns, accepters or VS,Ns, pairs, incorporated nitrogen also forms donor-type defects leading to compensation of holes. In undoped ZnSe layers, the results show presence of Zn vacancies in concentr ations 10(16)-10(17) cm(-3). The Zn vacancy concentration correlates with t he dislocation density at the ZnSe/GaAs interface.