N-TYPE DOPING OF THE WIDE-GAP TERNARY ALLOY (CDMG)TE DURING MOLECULAR-BEAM EPITAXY

We report on the n-type doping of the wide gap II-VI semiconductor CdMgTe. Bromine and chlorine have been used as dopants during molecular beam epitaxy. For the CdTe base material both bromine and chlorine give shallow donors, and free carrier concentrations of up to 2.8X10(18) cm(-3) have been reached. For increasing Mg concentration, however, deep donors are created, limiting the free carrier concentration at room temperature. This is demonstrated by Hall effect measurements at different temperature. The deep donors can be converted to metastable shallow donors by light illumination at temperatures below about 180 K, which results in persistent photoconductivity. We interpret our results in terms of a DX-like state, which is introduced by both the chlorine and bromine doping, and which moves into the band gap with increasing Mg concentration. We conclude that the limit in the n-type doping of CdMgTe, the band gap of which can easily be tuned through the whole visible range, is an intrinsic property of the dopants used, and not due to self-compensation caused by nonideal growth conditions.