Modulation Spectroscopy Methods in Photovoltaic Materials Research

This book is focused on the application of temperature dependent photo- and electroreflectance spectroscopy in order to study novel and potential materials in solar energy conversion. Photoreflectance and electroreflectance belong to the modulation spectroscopy techniques, where during reflectance measurements, the external modulation is applied in respect to one system parameter. Within the techniques used in this work, the periodically modulated parameter was the built-in surface/internal electric field. Changes in the electric field cause changes in the complex dielectric function and this in turn is directly related to the material reflectance ability. The recorded modulated reflectance spectra had a nature of a third derivative near the interband transitions. These methods allowed us to estimate the bandgap energy of studied materials with relatively high precision, and additionally to evaluate the quality of crystals. The main advantage of photo- and electroreflectance spectroscopies over other optical characterization techniques is that they are nondestructive, simple, applicable at room temperatures and high precision.