Optical absorption mechanisms in heterodimensional photodetectors

To improve upon the performance of GaAs metal-semiconductor-metal (MSM) photodetectors we developed a novel heterodimensional device by introducing a AlGaAs/GaAs heterostructure in such a a way that the two-dimensional electron gas (2DEG) of the heterostructure was in direct contact with the electrodes. This structural approach resulted in a significant reduction in dark current which is attributed to a decrease in thermionic emission produced by the lateral heterodimensional Schottky contact This lower noise floor allowed us to observe a structural signature in the optical spectral response of the heterodimensional photodetector at room temperature from photoresponsvity measurements. We have determined that a spectral response peak near the GaAs absorption edge results from variations in the complex dielectric permittivity throughout the GaAs layer produced by the AlGaAs/GaAs built-in electric field. In addition to developing a localized Franz-Keldysh model to represent variations in optical properties caused by the non-uniformity of the electric field a more complete analytical model of the AlGaAs/GaAs heterostructure was developed to more accurately predict the electric field profile. Finally, a propagation matrix approach was used to obtain the aggregate spectral photoresponsivity of the heterodimensional photodetector in order to verify the accuracy of the proposed spectral absorption model and to emulate the behavior of the device under applied bias.