GaAs/AlGaAs quantum well infrared photoconductors versus HgCdTe photodiodes for long-wavelength infrared applications

Abstract

Investigations of the performance of GaAs/AIGaAs quantum well IR photoconductors (QWIPs) as compared to HgCdTe photodiodes operated at temperatures below 77 K in the long-wavelength IR (LWIR) region are presented. In comparative studies, the current standard n+ -p HgCdTe photodiodes as well as p+ -n photodiodes are considered. Investigations of the fundamental physical limitations of HgCdTe photodiodes indicate better performance of this type of detector in comparison with QWIPs operated in the range 40 to 77 K. At 40 K, QWIPs with a cutoff wavelength of about 8 μm indicate higher detectivity. The advantage of QWIPs increases in wider spectral regions and at temperatures below 40 K. Usually, in the temperature range below 50 K the performance of n+ -p HgCdTe photodiodes is determined by trap-assisted tunneling. As a result, the advantage of GaAs/AIGaAs QWIPs increases in wider spectral regions (λ ≈ 8 to 12 μm) and at temperatures below 50 K. The comparison with p+ -n HgCdTe photodiodes is more complicated for lack of precisely modeled current transport in these junctions. GaAs/AIGaAs QWIPs at 40 K are background limited in low-background conditions. This observation plus the maturity of GaAs/AIGaAs technology and its radiation hardness characteristics promise that QWIP technology can produce high-quality focal plane arrays for space applications.