Minority carrier lifetime and noise in abrupt molecular-beam epitaxy-grown HgCdTe heterostructures

The steady-state lifetime of photogenerated minority carriers has been investigated in heterostructure HgCdTe devices fabricated on molecular-beam epitaxy (MBE) grown material. A wider bandgap capping layer (Hg(1-x)Cd(x)Te, x = 0.44) was grown on a narrower bandgap absorbing layer (Hg(1-x)Cd(x)Te, x = 0.32, lambda(co,80K) = 4.57 mum) material in an uninterrupted MBE growth to create an abrupt heterointerface. Steady-state lifetime as a function of temperature over the range 80-300 K was extracted from photoconductive responsivity at an optical wavelength corresponding to the peak responsivity at that temperature. At 80 K, the photoconductors exhibit a specific detectivity of 4.5 x 10(11) cm. Hz(-1/2) W-1 (chopping frequency of I kHz). For each measurement temperature, the steady-state excess carrier lifetime determined experimentally was compared to the theoretical bulk lifetime for material with x = 0.32 and effective n-type doping density of 3.7 X 10(14) cm(-1). Theoretical calculations of the Auger-1 lifetime based on expressions developed by Pratt et al. were not able to account for the reduction in lifetime observed at temperatures above 180 K. Two approaches have been attempted to resolve this discrepancy: A semiempirical expression for Auger lifetime attributed to Meyer et al. was used to fit to the data, with the Auger coefficient gamma as a fitting parameter. However, the resulting Auger coefficient found in this work is more than an order of magnitude higher than that reported previously. Alternatively, the reduction in effective lifetime above 180 K may be understood as a "loss" of carriers from the narrow bandgap absorbing layer that are promoted across the potential barrier in the conduction band into a low lifetime, wider bandgap capping layer. The reduction in lifetime as a function of inverse temperature for temperatures above 180 K may be fitted by a "cap lifetime" that has an activation energy equal to the change in bandgap across the heterostucture and scaled by a fitting constant.