Upstream modulation in photoreflectance

TL;DR

This paper demonstrates that in photoreflectance, probing higher energy levels than the pump beam is effective, expanding the technique's applicability for characterizing semiconductor electronic structures.

Contribution

The study reveals that upstream modulation in photoreflectance is feasible and effective, challenging the traditional energy sweeping limits and broadening potential applications.

Findings

Upstream modulation effectively probes high energy critical points.

E1 and E0+Δ0 critical points of GaAs are resolved with lower energy pump light.

Upstream modulation can extend the application range of photoreflectance.

Abstract

Photoreflectance is used for the characterisation of semiconductor samples, usually by sweeping the monochromatized probe beam within the energy range comprised between the highest value set by the pump beam and the lowest absorption threshold of the sample. There is, however, no fundamental upper limit for the probe beam other than the limited spectral content of the source and the responsivity of the detector. As long as the modulation mechanism behind photoreflectance does affect the complete electronic structure of the material under study, sweeping the probe beam upstream towards higher energies from that of the pump source is equally effective in order to probe high energy critical points. This fact, up to now largely overseen, is shown experimentally in this work. E1 and E0+{\Delta}0 critical points of bulk GaAs are unambiguously resolved using pump light of lower energy. Upstream modulation may widen further applications of the technique.