Effect of the modulation duty cycle on the amplitude of photoreflectance

Abstract

We have observed the behavior of photoreflectance (PR) spectra from a set of a molecular-beam-epitaxy-grown heterostructures as a function of the modulation duty cycle. This was done over a range of frequencies extending from 10–1000 Hz. By varying the duty cycle of the pump beam at different frequencies, we are able to find the duty cycle that gave the largest amplitude. While standard PR techniques use a 50% duty cycle, we have found that at low frequencies (10–30 Hz) the optimal value is between 30–40% in these particular sets of experiments resulting in as much as a 33% increase in amplitude. The change in the optimal values of the duty cycle from sample to sample was qualitatively correlated to the deep levels sample. PACS Nos.: 78.20.Ci, 78.40., 78.40.Fy