ZnS_1-xTe_x - based Schottky barrier UV photodetectors have been fabricated on several commonly available substrates (GaAs, GaP and Si). The photoresponse of the devices as a function of photon wavelength was measured using the Fourier transform interferometric technique. The external quantum efficiency was also measured using a standard optics setup with calibrated power meter....[ Read more ]

ZnS_1-xTe_x - based Schottky barrier UV photodetectors have been fabricated on several commonly available substrates (GaAs, GaP and Si). The photoresponse of the devices as a function of photon wavelength was measured using the Fourier transform interferometric technique. The external quantum efficiency was also measured using a standard optics setup with calibrated power meter.

The early structures (called type I) consist of an MBE-grown ZnSTe:Al active layer on GaAs substrates. A thin layer of Au was evaporated on top to form the Schottky barrier junction. The results of photoresponse measurement indicate that the response is sensitive to the conductivity type of the substrate and the difference can be well explained through the studies of their corresponding electron energy band diagrams. We have also investigated the photoresponse as a function of the doping level of the active ZnSTe:Al layer, of which the results are consistent with the expected dependence of the depletion region width and the photo-generated carrier lifetime upon the dopant concentration.

An optimized structure (called type II) was designed in which the active layer is an intrinsic ZnSTe epilayer grown homoepitaxially on a n⁺ - ZnSTe layer and the ohmic contact is made to the n⁺ - ZnSTe. Truly visible-blind UV sensitive response is obtained on the type-II structures with external quantum efficiency of 50% when grown on a GaP substrate and 40% when grown on a Si substrate. Measurements shown that about 30% of the incident radiation is lost to reflections. With suitable anti-reflection coating applied to the top of these device structures, a quantum efficiency higher than 70% should be realizable. These results indicate that ZnSTe-based Schottky photodiodes are very promising for use detection applications that require visible-blind response.