Wide Band Gap Photonics
Silicon photosensors are ubiquitous in modern technology. A multitude of silicon device types exist ranging from simple photodiodes to sophisticated high resolution imaging devices. There are, however limitations to silicon. Certain limitations, such as small signal size can be overcome by using device configurations that boost the signal with an internal signal gain, such as the avalanche photodiode and the recently developed silicon photomultiplier (SiPM). These devices are quickly replacing traditional vacuum-based photomultiplier tubes in many applications.
Such devices, do not remedy all of the limitations. The semiconductor bandgap of silicon fundamentally limits the performance of the SiPM in terms of spectral response and electronic noise. One way to address these limitations is to replace the silicon with a semiconductor material that has a wider band gap, which can potentially reduce noise by orders of magnitude.
AlGaAs is a good candidate material that RMD is exploring for making wide band gap solid state photomultipliers (WBG-SSPM). Prototype devices have been fabricated and our current research is focused on developing fabrication methods to reduce the noise characteristics.
Test AlGaAs diode with an etched optical window
4×5 test array of AlGaAs Geiger photodiodes