Abstract
Normal‐incident absorption in the recently‐demonstrated, p‐type quantum‐well infrared photodetectors is analyzed with the k⋅p theory, under the envelope‐function approximation. A first‐principles calculation of the infrared‐absorption spectra is performed with no adjustable parameter. The responsivity is evaluated from the calculated normal‐incident absorption and the experimentally‐derived photoconductive gain. Good agreement is obtained with measurements at λ<λc. The bandwidths of the infrared‐absorption spectra are found to be limited by spin‐orbit splitting as well as the overlap integrals.