EFFICIENT N-TYPE DOPING OF CDTE EPITAXIAL LAYERS GROWN BY PHOTO-ASSISTED MOLECULAR-BEAM EPITAXY WITH THE USE OF CHLORINE

Chlorine has been used successfully for the first time for n-type doping of CdTe epitaxial layers (epilayers) grown by photo-assisted molecular beam epitaxy. Similar to n-type doping of ZnSe layers, ZnCl2 has been used as source material. The free-carrier concentration can be varied over more than three orders of magnitude by changing the ZnCl2 oven temperature. Peak mobilities are 4700 cm2 V-1 s-1 for an electron concentration of 2 x 10(16) cm-3 and 525 cm2 V-1 s-1 for 2 x 10(18) cm-3. The electrical transport data obtained by Van der Pauw configuration and Hall structure measurements are consistent with each other, indicating a good uniformity of the epilayers. In photoluminescence the donor-bound-exciton emission dominates for all chlorine concentrations. This contasts significantly with results obtained for indium doping, commonly used for obtaining n-type CdTe epilayers. The superiority of chlorine over indium doping and the influence of growth parameters on the behaviour of CdTe:Cl layers will be discussed on the basis of transport, luminescence, secondary ion mass spectroscopy and X-ray photoelectron spectroscopy data.