DARK CURRENT GENERATING MECHANISMS IN SHORT-WAVELENGTH INFRARED PHOTOVOLTAIC DETECTORS

The current-voltage characteristics and quantum efficiencies of double layer planar heterostructure photodiodes were investigated. Results a re reported on devices with cutoff wavelengths of 1.8, 2.4, and 3.3 mu m. For these respective devices, the dominant currents for temperatur es >250, >200,>150K are diffusion currents Limited by shallow Shockley -Hall-Read (SHR) processes. The remarkable result is that the electric al and optoelectronic properties of these devices of diverse cut-off w avelength can be explained by simple models using independently measur ed layer parameters such as the minority carrier lifetimes. For all th ree cases, the analysis suggests that the same shallow (SHR) centers l ocated at 78% of the energy gap are causing the observed effects. Thes e traps located in the n-type base of the device are not influenced by the magnitude of n-type doping and this observation was used to signi ficantly improve the performance of the devices and validate the predi ctive capability of the models used in the analysis. The shallow cente rs appear to be process induced rather than grown-in. This assertion i s based on the observation that changes in the annealing process led t o an order of magnitude improvement in the minority carrier lifetime.