Enhanced terahertz absorption of quantum wells sandwiched between heavily doped contacts based on micro-cavity resonance

A novel high-efficiency microcavity structure of quantum wells sandwiched between periodic heavily Si-doped GaAs top contact gratings and bottom contact film has been proposed as the optical coupler of a terahertz quantum well photodetector (THz QWP). Similar to metal at visible light, highly doped semiconductors exhibit plasma frequencies at mid- and far-infrared wavelengths. The intersubband absorption spectra and electric field distribution of the microcavity THz QWP are calculated with the finite difference time-domain method. Our results indicate that the frequency of the surface plasmon polariton can be tuned to the microcavity resonant mode under an optimized structure and the intersubband absorption is efficiently enhanced by the microcavity structure. When the doping concentration of the contact exceeds 10¹⁸cm^-3, the intersubband absorption of the microcavity THz QWP at the response wavelength is over one order of magnitude higher than that of the standard 45° device. In addition, the angle of the incident light only influences the intensity of the absorptivity, indicating that the designed device was independent of the periodic surface structure.