Minority carrier lifetime measurements in Strained Layer Superlattices (SLS)

We propose the development of a system for measuring the minority carrier lifetime in strained layer superlattices (SLS). Mid wave infrared (MWIR) and long wave infrared (LWIR) detectors based on SLS technology show promise due to the large and inexpensive focal plane arrays that can be fabricated. The devices are held back though, by excessive dark current, which is related to a poor minority carrier lifetime. This poor lifetime limits SLS detector performance relative to the currently utilized HgCdTe devices. The proposed system will allow for quick, repeatable, and accurate measurement of minority carrier lifetimes so that SLS researchers can make progress in developing these promising devices. The system is based on the optical modulation response technique, but is also capable of time resolved photoluminescence measurements. Excess carriers are produced by fiber coupled semiconductor laser, and excess carrier concentrations as low as 3*10^13 per cm cubed have been obtained.