A Study of the Avalanche Multiplication and Excess Noise in Al_xIn_1–xAs_γSb_1-γ Avalanche Photodiodes Lattice-Matched to GaSb

High-sensitivity linear-mode avalanche photodiodes (APDs) that operate beyond 1.65 μm and up to 2 μm require a narrow bandgap that also gives rise to high dark currents, especially when subject to the large electric fields necessary for avalanche multiplication. This has led to increasing interest in separate absorption, charge, and multiplication (SACM) detectors where the narrow bandgap absorber has a low electric field and the wider bandgap multiplication region provides the gain. A systematic study of Al_0.7In_0.3As_0.31Sb_0.69 grown lattice-matched on GaSb as the multiplication layer has been undertaken on p–i–n structures varying in width from 0.1 to 1.5 μm and the ionization coefficients and excess noise extracted over a wide electric field range (195 kV/cm–830 kV/cm). When integrated with a lattice-matched Al_0.3In_0.7As_0.64Sb_0.36 absorption layer, such an SACM APD is found to demonstrate a quantum efficiency of 64% and 10% for the wavelengths of 1.55 and 2 μm, respectively, at punch-through, without any antireflection coating. The device shows a maximum avalanche gain of 197 with an excess noise of 3.1 at a gain of 10. Such APDs can be potentially used in a receiver for many photon-starved applications, including gas sensing and LiDAR.