| Near infrared InGaAs photocathodes were designed and grown using molecular beam epitaxy (MBE), a high quality semiconductor growth technique, for the purpose of expanding the current spectral range of generation 3 image intensifier tubes to a 1000nm wavelength while maintaining a high quantum efficiency. Previous authors who have attempted this task have reported low sensitivity compared to the standard GaAs photocathodes and associated this drawback with the compositional mismatch from growing InGaAs epilayers onto GaAs substrates. Our approach differed from these previous authors by using MBE for the semiconductor growth instead of a vapor phase epitaxy technique that had been employed. In addition, to reduce the inherent lattice mismatch between the InGaAs photoemissive layer and the substrate, structures deviating from standard GaAs photocathodes were created, to include lattice-mismatch reducing buffers. These buffers are composed of ternary alloys with graded composition. Utilizing a variety of characterization techniques to determine growth parameters (thickness, doping, composition, crystallinity) a high level of control and reproducibility was achieved on our photocathode structures.; Overall, negative electron affinity activation performed on our InGaAs photocathodes showed improvements in their white light photoresponse (PR) resulting from the inclusion of these buffers. Studies performed using room temperature photoluminescence, Raman spectroscopy and atomic force microscopy were employed to attempt relating these increases in PR to changes in material parameters and are presented in this dissertation. |
