The cutoff wavelength and minority-carrier lifetime in implanted n+-on-bulk p Hg1−xCdxTe photodiodes

Abstract

The cutoff wavelength λco at 77 K of implanted n+-on-bulk p-type Hg1−xCdxTe photodiodes is calculated with the minority-carrier lifetime of the bulk material as a parameter: 1.24/λco=[T+81.9/3.267×104(1+x)] {18.88−53.61x− 1/2 ln [(kT/q) μnτn]} −0.3424+1.838x+0.148x4 (eV). The composition x is obtained from the zero-intercept transmission spectra measured at 300 K. The minority-carrier lifetime τn of the photodiodes and its temperature dependence have been obtained from the photodiode dynamic resistance at zero-bias voltage versus reciprocal temperature 1/T data. The temperature dependence of the minority-carrier mobility μn is also taken into account. The results indicate that the lifetime in the bulk p-type material is determined by Shockley–Read generation-recombination centers. For undoped, p-type substrates obtained from Cominco Inc., the trap energy is approximately 45 meV. Gold-doped crystals grown by the method of solid-state recrystallization exhibit a trap energy of the order of 30–35 meV.