Random alloy thick AlGaAsSb avalanche photodiodes on InP substrates

Abstract

We demonstrate low noise random alloy (RA) Al0.85Ga0.15AsSb (hereafter AlGaAsSb) avalanche photodiodes (APDs) nearly lattice-matched to InP substrates. In contrast to digital alloy (DA), RAs are manufacturable due to the ease of growth. The 910 nm-thick RA AlGaAsSb was grown at a low temperature around 450 °C to mitigate phase separation by suppressing surface mobility of adatoms. The high quality of the RA AlGaAsSb material was verified by x-ray diffraction, Nomarski, and atomic force microscope images. Capacitance–voltage measurement found that the background doping concentration was 6–7 × 1014 cm−3, indicating very low impurity density in the RA AlGaAsSb material. Current–voltage measurements were carried out under dark condition and 455 nm laser illumination at room temperature. The breakdown occurs at −58 V. The dark current density at a gain of 10 was found to be 70 μA/cm2. This value is three orders of magnitude lower than previously reported DA AlAs0.56Sb0.44 APDs [Yi et al., Nat. Photonics 13, 683 (2019)], one order of magnitude lower than DA AlGaAsSb [Lee et al., Appl. Phys. Lett. 118, 081106 (2021)], and comparable to RA AlInAsSb APDs [Kodati et al., Appl. Phys. Lett. 118, 091101 (2021)]. In addition, the measured excess noise shows a low k (the ratio of impact ionization coefficients) of 0.01. These noise characteristics make the RA AlGaAsSb multiplier suitable for commercial applications, such as optical communication and LiDAR systems.