PIN versus PN Homojunctions in GaInAsSb 2.0-2.5 Micron Mesa Photodiodes

The performances of a pin versus a pn structure from GaInAsSb materials operating at room temperature are compared both from a theoretical point of view and experimentally. Theoretically, it is found in materials limited by generationrecombination currents, pn junctions have a higher D* than pin junctions. The thinner depletion region of pn junctions results in a lower responsivity but a higher dynamic resistance, giving an overall higher D* compared to a pin structure. A series of five p+pn+ Ga0.80In0.20As0.18Sb0.82 detector structures latticed matched to GaSb substrates and with 2.37 μm cut off wavelength were grown by molecular beam epitaxy and processed into variable size mesa photodiodes. Only the doping of the absorbing (p) region was varied from sample to sample, starting with nominally undoped (~1x10 cm pbackground doping due to native defects) and increasing the doping until a p+n+ structure was attained. Room temperature dynamic resistance-area product R0A was measured for each sample. A simple method is presented and used to disentangle perimeter from areal leakage currents. All five samples had comparable R0A’s. Maximum measured R0A was 30 Ω-cm in the largest mesas. Extracted R0A’s in the zero perimeter/area limit were about ~50 Ω-cm (20-100 Ω-cm) for all samples. Within uncertainty, no clear trend was seen. Tentative explanations are proposed.