P-type doping of beryllium chalcogenides grown by molecular beam epitaxy

We have grown Be-chalcogenides for the first time by molecular beam epitaxy (MBE) on GaAs substrates. The lattice constants of both BeTe and BeSe are smaller than that of GaAs, therefore Be containing compounds such as (BeMg)Te or (BeZn)Se and (BeMgZn)Se are ideal candidates to replace ZnTe or Zn(SSe) and (Zn Mg)(SSe) ternaries and quaternaries, respectively, In this contribution we present first results on the p-type doping of such layers using a modified nitrogen plasma source. The p-type dopability of BeTe as determined by van-der-Pauw measurements is comparable to that of ZnTe, free-hole concentrations of more than 1x10(20) cm(-3) have been reached. Heavily p-doped ternary (BeMg)Te or (BeMn)Te layers are obtained easily which are fully lattice-matched to GaAs. On the other hand, (BeZn)Se and (BeMgZn)Se ternaries and quaternaries seem to behave similar to their sulphur-containing counterparts, an increase of the band gap leads to a decrease of the free-hole concentration. Based on these results, we propose an alternative for the p-type doping of wide gap II-VI semiconductors. The small lattice mismatch of BeTe to GaAs allows to grow BeTe/ZnSe superlattices with excellent structural quality. We have calculated possible superlattice structures which should have an effective band gap comparable to or higher than ZnSe and at the same time are highly p-doped and almost lattice-matched to the GaAs substrate.