Metal-organic vapor-phase epitaxy growth and characterization of thick (100) CdTe layers on (100) GaAs and (100) GaAs/Si substrates

The growth characteristics and crystalline quality of thick (100) CdTe-epitaxial layers grown on (100) GaAs and (100) Ga-As/Si substrates in a metal-organic vapor-phase epitaxy (MOVPE) system for possible applications in x-ray imaging detectors were investigated. High-crystalline-quality epitaxial layers of thickness greater than 100 mum could be readily obtained on both types of substrates. The full width at half maximum (FWHM) values of the x-ray double-crystal rocking curve (DCRC) decreased rapidly with increasing layer thickness, and remained around 50-70 arcsec for layers thicker than 30 mum on both types of substrates. Photoluminescence (PL) measurement showed high-intensity excitonic emission with very small defect-related peaks from both types of epilayers. Stress analysis carried out by performing PL as a function of layer thickness showed the layers were strained and a small amount of residual stress, compressive in CdTe/GaAs and tensile in CdTe/GaAs/Si, remained even in the thick layers. Furthermore, the resistivity of the layers on the GaAs substrate was found to be lower than that of layers on GaAs/Si possibly because of the difference of the activation of incorporated impurity from the substrates because of the different kinds of stress existing on them. A heterojunction diode was then fabricated by growing a CdTe epilayer on an n(+)-GaAs substrate, which exhibited a good rectification property with a low value of reverse-bias leakage current even at high applied biases.