Random alloy thick AlGaAsSb avalanche photodiodes on InP substrates

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 degrees 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 x 10(14) 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 mu A/cm(2). 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.

Automated summary

In this study, low noise random alloy (RA) AlGaAsSb avalanche photodiodes (APDs) with nearly lattice-matched InP substrates were demonstrated. The RA AlGaAsSb material, grown at a low temperature, exhibited high quality and low impurity density. The APDs showed low dark current density and excess noise, making them suitable for commercial applications such as optical communication and LiDAR systems.