Abstract

Infrared detectors using intersubband absorption in quantum well structures have been of great interest in recent years. Both inter-conduction-subband and inter-valence-subband detectors have been fabricated already and proved to be of potential application for future communication purposes. For inter-conduction-subband detectors, the selection rule which limits the detection or absorption when the light is incident normally to the quantum well layers (parallel mode absorption) was overcome by the use of anisotropic materials such as Si(110) or Ge. The structure is often doped heavily (~10¹³cm^-2 or ~10¹⁹cm^-3) to obtain practical absorption coefficients (~10⁴cm^-1). In such a heavy doping case, many-body effects such as depolarization effect and exciton-like effect change the transition energy [1]. However, the transition energy cannot be estimated precisely based on the previous works, especially for the heavy doped structures. In addition, the free carrier absorption [2], which occurs simultaneously with the intersubband absorption, distorts the absorption spectrum greatly, especially for long wavelength regions. It often hides the peak position of parallel-mode intersubband absorption spectrum, which means the transition energy of parallel-mode absorption cannot be obtained only from the experimental absorption spectrum. Therefore, the distinction between the intersubband absorption and the free carrier absorption is needed. However, the free carrier absorption in two-dimensional structures grown on anisotropic materials has not been modeled to the authors’ knowledge.

© 1998 IEEE