Anne Migan-Dubois

Link between crystal quality and electrical properties of metalorganic vapour phase epitaxy InxGa1−xN thin films

We report on the crystal quality of metalorganic vapour phase epitaxy-grown InGaN with indium content ranging from 0% to 20%. Absorbance measurements are fit to a model including band tails and a defect represented as a Brendel oscillator (R. Brendel, Appl. Phys. A 50, 587, 1990). Band tail absorbance, corresponding to contorted bonds, increases with increased In content. Above 10% of In, the presence of another defect, the concentration of which increases with In content, has been correlated with x-ray diffraction and Raman. We suggest that this defect corresponds to nitrogen vacancies, in agreement with a reported model for GaN.

Subgap modulated photocurrent spectroscopy and its application to the study of the solar cell absorber defect distributions

In this paper, a theoretical background of subgap modulated photocurrent experiment is presented. It allows the investigation of the density of states DOS distribution, directly from the active region of a semiconductor heterojunction device. The junction is illuminated with a modulated subgap light excitation i.e., light with photon energy lower than the band gap of the active layer. Under specific considerations for the applied reverse bias voltage and the bias-light level, a simple theoretical relation of the imaginary part of the photocurrent versus the modulation angular frequency allows the determination of the energy profile of the gap states. This technique has been successfully applied to a Ga free CuIn,GaSe2 based solar cell to investigate the DOS distribution in the band gap of the absorber. Two distinct defect distributions have been exhibited in the absorber layer of the studied solar cell.