In-situ ellipsometric study on composition-dependent short-wave HgCdTe in the process of molecular beam epitaxy growth

Hg1-xCdxTe is considered as the preferred material for high performance infrared photodetectors and imaging focal plane array (FPA) detectors. One of the technical challenges of multi-dimensional integrated HgCdTe epitaxy by molecular beam epitaxy (MBE) lies in the in-situ extraction, characterization and precisely control of a series of parameters such as alloy composition, surface roughness, substrate temperature and film thickness at a relatively low substrate temperature of about 180 degrees C. Therefore, an in-situ, nondestructive spectroscopic ellipsometry (SE) method is needed to characterize the performance of HgCdTe films. In this paper, real time optical property characterization of short-wave Hg1-xCdxTe epitaxial grown by MBE is reported. Run to run feasibility and stability of in-situ SE is confirmed by buffer layer thickness verification in multiple growth runs. Lorentz oscillator parametric model provides a new approach to describe optical dispersion property of HgCdTe over spectral range of 1.5-4.1 eV. The absorption peaks show blue shift with the increase of HgCdTe Cd composition (x). Under this circumstance, the longitudinal x value for HgCdTe during epitaxy process can be obtained in real time without any surface damage by successfully building a composition-dependent optical constant library, with routine run-to-run reproducibility measurement accuracy Delta x of similar to 0.0015. This work will facilitate the fabrication of HgCdTe heterojunctions with complex component distribution and doping profiles.