Time-Resolved Photoluminescence Study of Carrier Recombination and Transport in Type-Ⅱ Superlattice Infrared Detector Materials

摘要

Time-resolved photoluminescence (TRPL) is used to study the minority carrier lifetime in type-Ⅱ superlattice (T2SL) infrared detector materials to investigate the recombination mechanisms, trap states and transport properties that currently limit their performance. Measurements of carrier lifetime have shown that InAs/Ga_(1-x)In_xSb T2SLs are dominated by non-radiative Shockley-Read-Hall (SRH) recombination, resulting in short minority carrier lifetimes (10's of nanoseconds at 77 K). A trap energy of ～60 meV above the valence band is identified in mid-wavelength infrared n-type InAs/Ga_(1-x)In_xSb T2SLs, where trap saturation (non-exponential decay) is observed under high injection levels due to a significantly faster hole capture rate than electron capture rate. Lifetime measurements in "Ga-free" InAs/InAs_(1-x)Sb_x T2SLs exhibit an order-of-magnitude increase in lifetime (100's of nanoseconds at 77 K) with contributions from both radiative and non-radiative recombination. This improvement is attributed to the reduction of non-radiative recombination centers from the superlattice with the elimination of Ga and suggests that the SRH trap(s) limiting the carrier lifetime of InAs/Ga_(1-x)In_xSb T2SLs is native to the Ga_(1-x)In_xSb layer. Additionally, radiative recombination is observed in an InAs/GaSb T2SL using a sub-bandgap CW laser to saturate the SRH recombination centers, yielding a radiative lifetime of ～140 ns at 77 K. Since carrier transport is a concern in Ga-free T2SLs, it is investigated by studying samples grown with and without barriers (to contain injected carriers to the absorber region). It is determined that carrier transport is poor in InAs/InGa_(1-x)In_xSb T2SLs because negligible differences are observed in the carrier lifetime.