Quantitative model for photocurrent spectroscopy of quantum‐well diodes including transit‐time and background‐doping effects

We present a simple model for photocurrent spectroscopy of quantum‐well p‐i‐n diodes that provides a quantitatively accurate desciption of the dependence of photocurrent on absorption coefficient and applied bias. The model incorporates the transit‐time effect described previously [R. P. Leavitt and J. L. Bradshaw, Appl. Phys. Lett. 59, 2433 (1991)] as a limiting case. It also includes the two major effects of residual background doping in the intrinsic region of the diode: nonuniform electric fields, which affect the transport of carriers, and incomplete depletion at low electric fields, which reduces the amount of photocurrent collected. We show that the background‐doping effect alone can mimic the transit‐time effects: reduction in the overall carrier collection efficiency, saturation of photocurrent spectral features, and the presence of minima in photocurrent where absorption spectra show maxima. We obtain a closed‐form expression for the photocurrent in the general case where both transit‐time and b...