Low temperature thermoreflectance of AlxGa1-xAs/GaAs quantum wells

Reflectance (R) and thermoreflectance (TR) of quantum well structures grown by MBE have been investigated at low temperature (30 K) in order to demonstrate the capabilities of TR to study quantum confined systems. Our results show that low temperature TR is a simple and yet very efficient technique which provides large signals (ΔR/R>103), also in the case of reduced-dimensionality systems. We also show that TR can extract spectroscopic information from relatively high background reflectance and that it can be used to study transitions between subbands higher than the fundamental ones. The TR modulation mechanisms are discussed and the TR and R lineshapes are compared. The first-derivative nature of TR allows for a straightforward and reliable comparison between experiment and theory; this feature may have interesting applications in the study of QWs and SLs, where interference effects from the multilayer structure may complicate the analysis of the spectra.