The performance of GaAs/AlGaAs asymmetric quantum well infrared detectors exhibiting inter subband absorption has been studied. The asymmetric quantum well structure considered for the present study consists of two regions, a step quantum well with a 100_ Al.18Ga.82As step and 80_ GaAs well, followed by a double barrier tunneling structure with 50_ Al.44Ga.56As barriers and a 40_ Al.2Ga.8As well. The quantum well structure has three bound to bound energy levels, one below the step (E1) and the other two above the step (E2 & E3). Transitions from E1_E2 and E1_E3 are employed for dual band detection. The energy difference E1_E2 and E1_E3 changes with the applied voltage due to stark effect. The absorption coefficient calculated at zero bias reaches the peak at 11_m and 17_m corresponding to the transitions from E1_E3 and E1_E2 respectively. However with increasing applied bias the absorption coefficient peaks for smaller wavelengths. Fig.2 shows the variation of absorption coefficient with respect to wavelength at different bias voltage. Resonant tunneling occurs at 20mV and 80mV for E1_E3 and E1_E2 transitions corresponding to 10_m and 14_m respectively. Photo generated carriers then tunnel through the double barrier structure. Thus the photocurrent is generated by inter subband absorption followed by resonant tunneling phenomena. The responsivity reaches a maximum of 0.37A/W at 20mV corresponding to 10_m and 0.48A/W at 80mV corresponding to 1.066¥10 6 (cm÷Hz/W) at 20mV and 1.319¥10 6 (cm÷Hz/W) at 80mV.
Journal: TechConnect Briefs
Volume: Technical Proceedings of the 2000 International Conference on Modeling and Simulation of Microsystems
Published: March 27, 2000
Pages: 372 - 375
Industry sector: Sensors, MEMS, Electronics
Topic: Modeling & Simulation of Microsystems