Analysis of Photocurrent Spectra of SiGe/Si Quantum-Well Solar Cell

A simple theoretical model is proposed to quantitatively explain the dependence of photocurrent spectra for multiple quantum-well (MQW) p-i-n diode on the absorption coefficient and the applied reverse bias. Excellent agreement is obtained between model calculation and the experimental photocurrent spectra for a 30-period 15-nm Si_0.85Ge_0.15/15-nm Si MQW p-i-n diode, where the background doping density and the built-in potential are treated as adjustable parameters. Using the model, the absorption coefficient extracted from the measured photocurrent spectra at low bias is in well agreement with the directly measured absorption coefficient. Also, the model parameters (the background doping density and the built-in diode potential) are in excellent agreement with the values of these quantities independently measured by C-V method. In terms of this model, the relation between the background doping and the photocurrent response is analyzed.