Next generation IR sensor technology for space applications at AIM

Abstract

Next generation infrared sensor space applications are based on technological evolutions on many frontiers. Sensor material improvements and device developments are two of them. This presentation reports on the latest results on HgCdTe (MCT) very long wavelength infrared (VLWIR) photovoltaic (PV) sensors and on the development of short wavelength infrared (SWIR) avalanche photodiodes (APDs). The dark current of photodiodes increases exponentially with increasing cut-off wavelength. To keep the dark current at an acceptable level, operational temperatures of MCT PV sensors with photo-sensitivity above 12 μm wavelength are typically around 50 K. Therefore, until recently, VLWIR MCT detectors have been built with photoconductive (PC) linear arrays or small 2D arrays enabling the higher operational temperatures of PC sensors (80 K - 120 K). The increasing interest in VLWIR imaging spectrometers requires larger 2D arrays excluding PC technology. One approach for feasible PV arrays is a significant reduction of the dark current by using extrinsically doped (in contrast to vacancy doped) p-MCT material. This allows for enhanced performance at convenient temperatures of 50 - 55 K. Alternatively, standard performance at higher operational temperatures at 60 K - 70 K is possible. AIM presents the latest results on its extrinsically p-doped VLWIR MCT photodiodes with a 15 μm cut-off wavelength. At the other side of the IR spectrum, AIM has a strong focus on focal plane arrays for low-photon flux SWIR applications. For some applications, the sensitivity of SWIR arrays with capacitive transimpedance amplifier input stages is not sufficient and APDs are required. AIM presents the latest results on its SWIR APD devices.