Abstract

A modulated spectroscopy method called photoreflectance is described. The technique involves using an incident beam and a coincident modulating beam usually from a diode laser. The former results in a reflectance signal while the latter gives a modulated reflectance signal. By fitting the spectrum of the normalized modulated reflectance with a third order derivative of the dielectric function, the critical point energies can be determined with high accuracy. Two photoreflectance spectroscopy instruments with high throughput are discussed. The use of these instruments is illustrated by examples from biaxially stressed silicon on insulator substrates and thin film photovoltaic devices. A recent method to suppress spurious modulated light from entering the photodetector is also briefly discussed.