Charge non-neutrality in the quantum well region of a GaAs-AlGaAs intersubband 9 μm detector

Infrared transmission is employed to study intersubband transitions in a GaAs-AlGaAs quantum well detector with spectral response peaked at about 9 μm. Under dc bias, our experiments show directly that the density of electrons in the doped quantum wells changes significantly, i.e., a charge non-neutrality occurs in the multiquantum well region of the detector. This degrades the detector internal quantum efficiency. Theoretical calculations compared with our experiments show that under a dc bias, the intersubband transition energy shifts are dominated by many-particle effects when the electron density in the well is changed; while the Stark shift is expected to dominate when the electron density remains constant.