Photoreflectance mapping of InGaAs HEMT wafers

Screening of device epilayers is now accepted as a critical issue in the research and development of high-performance semiconductor devices. Photoreflectance (PR) is very attractive for this purpose, since the composition and the built-in dc electric field of wafers can be estimated by analyzing the Franz-Keldysh oscillations (FKOs) in the PR spectra. Additionally, the laser excitation used is extremely weak which makes this method effectively non-invasive. Despite of these advantages, to our knowledge, on-wafer mapping by PR has not been reported. This paper presents PR mapping equipment and its application to InAlAs/InGaAs HEMT wafers. We visualize the non-uniform composition of InAlAs layers to show that PR mapping is a powerful tool for noninvasive wafer screening