Wavelength extended 2.4 μm heterojunction InGaAs photodiodes with InAlAs cap and linearly graded buffer layers suitable for both front and back illuminations

Using heterojunction structure with relative thin linearly graded InxAl1−xAs as buffer layer and In0.8Al0.2As as cap layer, wavelength extended In0.8Ga0.2As photodiodes with 50% cut-off wavelength of 2.42 μm at room temperature have been grown by using gas source MBE with a convenient but reliable procedure, and their performance over a wide temperature range have been extensively investigated. This structure with wider bandgap buffer and cap is suitable for both front and back illuminations. For those photodiodes with 500 μm mesa diameter, the typical dark current (VR = 10 mV) and R0A are 160 nA/137 Ω cm2 at 290 K, and 26.7 pA/1.08 MΩ cm2 at 150 K, respectively for doping level of 1E17 cm−3, at this higher doping level decrease in the response and appearance of unusual spectrum were also observed, which leaves a room for the careful optimization of the doping and structure.