This work proposes an engineering model for thermal radiation absorption due to direct intersubband transitions in doped semiconductors, which are excitations of bound electrons in the infrared spectral region. An existing quantum-mechanical approach is to model these transitions as a continuum of damped harmonic oscillators. This study modifies this approach to yield a more effective method for determining the optical constants of doped semiconductors. The room-temperature absorptance spectra of p-type GaAs samples with dopant concentrations from 8 × 1017 to 1 × 1020 cm-3 are measured using a Fourier transform–infrared spectrometer in the spectral region from 1.5 to 25 μm. The fitting of these spectra using the proposed model combined with the Drude and Lorentz models provides the optical constants and the dependence of the adjustable parameters on dopant concentration. The measured and fitted spectra agree closely. Potential applications of the model are semiconductor process control and infrared detector design.

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