Compressively strained p-type InGaAs/AlGaAs quantum-well infrared photodetectors

The compressively strained p-type In _0.15Ga _0.85As/ Al _0.33Ga _0.67As quantum-well infrared photodetectors (QWIPs) with different Be concentrations in their wells, which detect normal infrared incidence, were investigated. The QWIPs with a Be doping density of 10 ¹⁸cm ^-3 in the wells show a cutoff wavelength of 7.9 μm and basically symmetric detectivities of about 8×10 ⁸cmHz ^1/2/W at 600 Hz. By increasing the Be doping density in the wells to 2×10 ¹⁹cm ^-3, the cutoff wavelength is blueshifted to about 7.25 meV and the photoresponsivity and detectivity become asymmetric. The detectivity is increased to about 1.4×10 ⁹cmHz ^1/2/W at positive biases but significantly reduced at negative biases. The blueshift in the cutoff wavelength for the QWIP devices with heavy doping concentration in the wells is mainly due to the band-gap shrinkage and the increased well width while the asymmetric behavior in the photoresponsivity and detectivity is likely due to the inhomogenity resulting from dopant diffusion at high doping.