Avalanche photodiodes beyond 1.65 μm

Abstract

There are many applications where the ability to detect optical signals in the 1.65 - 3 μm wavelength range would be of considerable interest. In this paper we discuss two technologies that offer considerable promise for high speed, high sensitivity detection in this region utilising avalanche gain. InGaAs/GaAsSb Type II superlattices as the absorption region and InAlAs as the multiplication region can be combined to form a separate absorption and multiplication (SAM) avalanche photodiode (APD), all grown lattice matched on InP substrates. Detection at room temperature up to 2.4 μm can be readily achieved as can gains in excess of 40. InAs homojunction p-i-n diodes are capable of detecting light with wavelengths > 3 μm, even at 77 K. Although controlling the surface leakage current is a major challenge in mesa devices of InAs, gains in excess of 40 have also been obtained in these devices at room temperature. InAs is also the only III-V semiconductor material that appears to show excess noise-free avalanche gain when electrons are used to initiate the avalanche multiplication. We will discuss recent developments in these two material systems to date and the current state of the technology.