II-VI semiconductors with wide-band gap are currently under intense investigation for optoelectronic application in the green-UV range. However, due to the self-compensation effect specific to wide band-gap semiconductors, it is difficult to realize the low resistive p-type ZnSe crystal. The growth of phosphorus-doped p-type conductive ZnTe single crystal has been achieved by the vertical gradient freezing (VGF) method . Using phosphorus-doped ZnTe substrate as a p-type conductor, it is expected the light emitter based on n-ZnSe/p-ZnTe heterojunction. In this paper, we report on the MBE growth of heteroepitaxial ZnSe layer grown on p-ZnTe substrates. While there existed 7.7% lattice mismatch between ZnSe and ZnTe crystal, the ZnSe/ZnTe heteroepitaxial films were successfully achieved on the ZnTe substrate.
The ZnSe layers were grown by MBE using conventional molecular beams on the phosphorus-doped p-type ZnTe(001) substrates grown by the VGF method. The substrate temperatures, Tg, were controlled at the temperature range from 150C to 250C. After thermal treatment of the ZnTe substrates, the ZnSe film was directly grown on the substrate by MBE method.
After the 3 hrs growth, while the RHEED patterns became spotty at Tg of 150C, the streak patterns are obtained above 200C. These results imply the 2-dimensional growth of the ZnSe on the ZnTe substrate. The I1d with LO-phonon, Iv and Y line emissions were dominated in the ZnSe films grown at Tg above 200C. Comparing with these emissions, both Ex and I2 emission intensities were too weak. Our results suggest that the ZnSe films could be grown on the ZnTe substrate by MBE, and it is expected the hetero p-n junction LEDs based on the p-type ZnTe substrate.
The authors would like to acknowledge Dr. K. Sato, Dr. T. Asahi, A. Arakawa, Nikko Materials Co., Ltd, for the supporting of ZnTe substrates.
K. Sato et. al., J. Crystal. Growth 214/215 (2000) 1080.