Characteristics of dark current and photocurrent in superlattice infrared photodetectors

Correspondence: Email: kuan@cc.ee.ntu.edu.tw; Telephone: +886-2-23635251 ext. 439; Fax: +886-2-23671909. The characteristics of a superlattice infrared photodetector, which has a 20-period GaAs/AlGaAs superlattice embedded between two AlGaAs current blocking layers are investigated. We propose a model to explain the conduction of dark current and photocurrent. In particular, the interesting feature of this detector, which can also be explained by our model, is bias redistribution due to the background photocurrent. With the background radiation incident upon the detector, the blocking layers are tilted up for 126meV at zero bias. The electrons are all confined by the tilt-up blocking layers and cannot tunnel through them. As the external bias increases, 70% of the voltage is added on the rear blocking layer and attempts to decrease its barrier height. Especially at -0.18V, the barrier is flat and the barrier height is 16.5meV higher than the bottom of the second miniband. In this case, only those photoelectrons with high enough energy can pass the blocking layer. As the external bias increases up to -0.33V, the rear blocking layer is tilted down for 105meV. The blocking layer seems to be transparent to all photoelectrons to tunnel through. In addition, the photo responsivity due to the short wavelength excitation indicates that the photoelectrons do have the inelastic relaxation of the energy along the growth direction.