Infrared imaging with quantum wells and strained layer superlattices

In the last few years infrared focal plane arrays based on Type-I GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) have been commercialized, providing excellent cost-effective imaging for security and surveillance and gas imaging applications. A second cooled infrared sensor technology that has made significant advances in recent years is photodiodes based on Type-II InAs/(In)GaSb strained layer superlattices (SLS). Imaging chips with upto a million pixels, quantum efficiency exceeding 50%, and cutoff wavelength exceeding 10 microns have been recently demonstrated. SLS offers the promise of the high quantum efficiency and operating temperature of longwave infrared mercury cadmium telluride (MCT) at the price point of QWIP and midwave infrared indium antimonide (InSb). That promise is rapidly being fulfilled. This paper presents the current state-of-the-art of both these sensor technologies at this critical stage of their evolution.