Dark Currents in a Fully-Depleted LWIR HgCdTe P-on-n Heterojunction: Analytical and Numerical Simulations

Abstract

In this paper, we use the theory of Evans and Landsberg, which is a generalization of the Shockley–Read–Hall recombination statistics in the space charge region (SCR), to include effects of Auger and radiative recombination processes that are also of origin in the SCR. Using analytical expressions for the current density, we calculate the total dark current density for a variety of conditions. Contributions include radiative and Auger transitions of origin in both the quasi-neutral region and the SCR. Numerical simulations are used to assess the nature of the limitations associated with the analytical calculation in the n-extrinsic region ( $$N_{\rm d} \gg n_{\rm i}$$ , where $$N_{\rm d}$$ is the doping concentration and $$n_{\rm i}$$ is the intrinsic carrier concentration), and to extend the calculations to operating temperatures in the intrinsic region ( $$n_{\rm i} \gg N_{\rm d}$$ ). Major findings include the observation that in a fully depleted $$P^+n$$ double-layer planar hetero-structure, at a reverse bias voltage sufficiently high to suppress the Auger process, SRH centers are not limiting, and the dark current is due to radiative transitions of origin in the n-side SCR. From the numerical simulations, while the Auger recombination rate changes drastically with varying the carrier concentration (such as applying reverse bias), the radiative recombination rate remains nearly invariant to varying the carrier concentration, and, as such, does not appreciably change with increasing reverse bias. Using the theory of van Roosbroeck and Shockley, the radiative recombination rate is obtained by integrating the measured optical absorption coefficient over all photon energies. Hence, the theory links the measured absorption coefficient to the measured dark current density for conditions in which the dominant current component is due to radiative recombination. Finally, the numerical simulations reveal, in both the n-extrinsic and intrinsic operating regions, that, under sufficient conditions, the detector is radiatively limited.