Aluminum diffusion in ZnTe films grown on GaSb substrates for n-type doping

ZnTe PN homojunctions are fabricated using thermal diffusion of Al into a ZnTe film grown on lattice-matched GaSb substrates by molecular beam epitaxy. Rectifying J-V characteristics and the photovoltaic effect are observed which suggests that n-type ZnTe has been successfully achieved. The reverse bias breakdown voltage is found to be dependent on annealing condition and acceptor concentration, and the trend agrees with PN junction theory. Secondary ion mass spectrometer depth profiles of the Al film show that Zn and Te out-diffuse into the Al film during annealing. This out-diffusion is undesirable because it may result in Zn vacancies which compensate Al donor atoms. Photoluminescence measurements of annealed ZnTe samples without the Al diffusion layer show strong band-edge luminescence at room temperature. Midgap luminescence also appears for annealed samples but the intensity is lower than the band-edge peak. This technique may lead to a better understanding of the n-type doping problem for ZnTe, and could lead to in-situdoping techniques and treatments. Successful n-type doping of ZnTe with low resistivity will enable high-efficiency optoelectronic devices operating at pure-green wavelengths (550 nm).