MBE grown mid-infrared HgCdTe avalanche photodiodes on Si substrates

Modern weapon systems need to detect, recognize, and track a variety of targets under a wide spectrum of atmospheric conditions. They include stationary and mobile targets against complex backgrounds and landmines. A number of active systems like hybrid LIDAR-RADAR systems, heterodyne detection as well as passive systems like thermal imagers have been proposed and developed to meet this objective. Most ground-based and air-based systems would operate at long distances. The return laser signal from the target is not only attenuated by absorption, reflection and scattering by air-borne gas, dust and liquid particles, but also by the emissivity and reflectivity variations of the target surface. High bandwidth detectors with internal gain are required. Avalanche photodetectors (APDs) are best suited for this purpose due to their high gain-bandwidth characteristics. Robust silicon-APDs are limited to visible and very near infrared region, while InGaAs works well up to certain wavelengths. On the other hand, it is important to realize that the atmospheric attenuation is wavelength dependent. Local changes in the air density yield random fluctuations in the refractive index, diverging the laser signal. Consequently, longer wavelength (MWIR: 3 - 5mum and LWIR: 8 -12mu m) source-detector systems are required to overcome the practical and seasonal conditions of the atmosphere. Previous efforts on HgCdTe APDs has been based on expensive CdZnTe substrates . The paper reports on the first HgCdTe based MWIR (3 - 5mum) APD grown on Si substrates by molecular beam epitaxy(MBE)