Analysis of III–V Superlattice nBn Device Characteristics

Abstract

Mid-wavelength infrared nBn detectors built with III–V superlattice materials have been tested by means of both capacitance and direct-current methods. By combining the results, it is possible to achieve clear separation of the two components of dark current, namely the generation–recombination (GR) current due to the Shockley–Read–Hall mechanism in the depletion region, and the diffusion current from the neutral region. The GR current component is unambiguously identified by two characteristics: (a) it is a linear function of the depletion width, and (b) its activation energy is approximately one-half the bandgap. The remaining current is shown to be due to diffusion because of its activation energy equaling the full bandgap. In addition, the activation energy of the total measured dark current in each local region of the temperature–bias parameter space is evaluated. We show the benefits of capacitance analysis applied to the nBn device and review some of the requirements for correct measurements. The carrier concentration of the unintentionally doped absorber region is found to be 1.2 × 1014 cm−3n-type. It is shown that the depletion region resides almost entirely within the absorber. Also, the doping in the nBn barrier is found to be 4 × 1015 cm−3p-type. Minority-carrier lifetimes estimated from the dark current components are on the order of 10 μs.