Novel method of modulation spectroscopy for heterostructures: Electro-photoreflectance

A new modulation spectroscopy for studying the optical transition energies of layered electronic materials is presented. The method is based on a superposition of the modulation field produced by illumination of a laser and the field produced by external voltage to maintain a constant surface field unchanged, giving rise to reflectance signals due to the buried layer. A comparison of the present method with conventional electroreflectance and photoreflectance methods reveals that the present method (called electro-photoreflectance) picks out the reflectance signals from the buried layers but not those from the front surface.