Impact ionization Characterisation of Al0.70In0.30As0.74Sb0.26 p-i-n and GaAs/Ga0.96AsBi0.04 MQW photodiodes

The goal of this work is to first, characterize the impact ionization properties of Al0.70In0.30As0.74Sb0.26 for its potential application as the avalanche multiplication layer in separate absorption and multiplication avalanche photodiodes (SAM-APDs) on an InP substrate for optical communication systems. Previous studies on AlAs0.56Sb0.44 homojunction diodes were systematically investigated at room temperature. It was found that the bulk electron and hole ionization coefficients, α and β respectively, differ significantly, exhibiting "silicon-like" behaviour at low electric fields and noise showed the excess noise on an InP substrate, with k=0.005. However, this material is prone to oxidation and surface leakage current. These issues are significantly mitigated by using the AlInAsSb quaternary alloy system, which offers improved stability and reduced leakage. In this work, the multiplication, ionization coefficients, and excess noise characteristics for the AlInAsSb alloy on an InP substrate were presented over an electric field range of 0.33–0.6 MV/cm. These findings provide valuable insights for the design and optimization of high-performance shortwave infrared (SWIR) Separate Absorption, Charge, and Multiplication (SACM) Avalanche Photodiodes (APDs) using an AlInAsSb multiplication layer on commercially viable InP substrates.
Secondly, characterize the impact ionization coefficients of GaAs/GaAsBi multiple quantum well. In previous research, the systematic analysis on the series of bulk GaAsBi p-i-n and n-i-p samples, with varying intrinsic region thicknesses and bismuth content revealed a significant disparity between electron and hole ionization coefficients. In this research, introducing thin layers of GaAsBi as quantum wells (QWs) within a GaAs matrix can enhance the performance of avalanche structures. For the first time, a systematic study of avalanche multiplication in a series of GaAsBi/GaAs multiple quantum well (MQW) structures grown in a p-i-n configuration was undertaken, and their ionization behaviours was examined through photomultiplication measurements. The α/β ratio in GaAs was increased by suppressing hole impact ionization, achieved by modifying the valence band structure.