Retrieve the carrier population and built-in potential alignment in multi-quantum-well GaAs/InGaAs p-i-n photodiode

Abstract

Quantum wells (QWs) are widely adopted in pn junctions to extend the cut-off wavelength for photodetection and solar energy conversion , in which the built-in electric field plays essential role in extracting the photo-carriers from QWs but inevitably affected by practical factors like the background doping. Herein, the carrier distribution and potential alignment in GaAs/InGaAs multi-quantum-well p-i-n photodiode were investigated by scanning capacitance microscopy (SCM) and Kelvin probe force microscopy (KPFM). Three of the five QWs were found injected by electrons with population density up to 7 × 10 16 cm −3 in maximum according to the numerical simulation. The unintentionally doping concentration was estimated to be 5 × 10 15 cm −3 in the absorption area, this led to a narrowed space charge region by 355 nm from expectation, which was well proved by the KPFM measurement. Nevertheless, the change of built-in potential could reach 0.577 V corresponding to a fairly high open-circuit voltage of the photodiode under illumination with modest intensity. Our study provides direct insight into p-i-n multi-quantum-well structures for high efficiency photoelectric conversion. • For multi-quantum-well GaAs/InGaAs p-i-n photodiode: • The actual carrier and built-in potential distributions were disclosed by KPFM and SCM. • The built-in potential was measured as 1.21 V which decreased under illumination indicating a high V OC . • The unintentionally doping in absorption area led to shrinkage of depletion region and high population of electrons in quantum wells according to numerical simulation.