High detectivity AlGaAsSb/InGaAsSb photodetectors grown by molecular beam epitaxy with cutoff wavelength up to 2.6 μm

In this paper, we report AlGaAsSb/InGaAsSb heterojunction p–i–n photodetectors lattice-matched to GaSb substrates grown by solid source molecular beam epitaxy using As and Sb valved crackers. The use of valved crackers greatly facilitated the lattice-matching of the quaternary InGaAsSb absorbing layer to the GaSb substrates, as characterized by X-ray diffraction. The growth temperature of the absorbing layer in the device was kept at 450 °C. The V to III flux ratio was optimized based on comparison studies of the strength of photoluminescence (PL), which indicated excellent material quality of the InGaAsSb active layer lattice-matched to the GaSb substrates. The device structure was designed to be optimized for the maximum quantum efficiency. The p–i–n photodetectors were processed using wet chemical etching and standard photolithographic process. The resulting devices exhibited low dark current and a breakdown voltage of 32 V at room temperature. A record Johnson-noise-limited detectivity of 9.0×1010 cm Hz1/2/W was achieved at 290 K. The 50% cutoff wavelength of the device was 2.57 μm. Thus, our result has clearly demonstrated the potential of very high-performance lattice-matched InGaAsSb p–i–n photodetectors for the mid-infrared wavelengths, comparable or superior to the current InGaAs photodiodes on InP substrate with extended wavelengths.