High Operating Temperature Planar MWIR FPA Based on Type-II Superlattices

Type II superlattices (T2SL) represent a promising material system capable of delivering more producible, large-format broadband MWIR and LWIR focal plane arrays (FPAs). High temperature operation of current MCT based FPAs is limited by inherent defects in the II-VI material and strong Auger recombination. T2SLs are based upon more mature III-V materials and should give better material quality, lower substrate costs, lower Auger recombination rates and compatibility with industrial III-V foundry processes. However, current T2SL based FPAs are based on mesa-isolated pixels. The need for an etched trench to isolate the mesas limits the pixel pitch due to the challenges of the required deep mesa-etching and the need to subsequently passivate the mesa sidewalls. Passivation is especially problematic when the pixel pitch is scaled down to few micrometers, especially for LWIR FPAs and MWIR FPAs at high operating temperatures. Even though a variety of methods of passivation of T2SL photodetectors have been reported, dark current reduction for small size pixels is still very challenging. One solution to this issue is to simply remove the mesa-sidewalls entirely by using planar structure. So far, no viable planar processing techniques have been demonstrated for T2SL; they currently rely on mesa isolated diodes. It is desirable to pursue planar processing techniques that are compatible with T2SL.  We present novel planar design for planar engineering for T2SL. The planar T2SL device is based on using diffusion approach to introduce the selective area doping. This approach is less damaging to the T2SL structure and economically justified. We propose diffusion method, to create top p-type or n-type top contact on a narrow-band gap T2SL absorbing region with opposite doping concentration. The key feature for the design is planar p-on-n or n-on-p device.