Reflectance and photoreflectance for in-situ monitoring of the molecular beam epitaxial growth of CdTe and Hg-based materials

Epitaxial growth of Hg-based semiconductors by molecular beam epitaxy (MBE) and metalorganic MBE (MOMBE) has progressed sufficiently to shift emphasis to the control of factors limiting the yield of both materials and devices. This paper reports on anex-situ study to evaluate the suitability of reflectance and photoreflectance (PR) asin-situ characterization techniques for the growth of CdTe and HgCdTe. Photoreflectance yields information about CdTe layers, with largest utility for doped and multi-layer structures. However, caution must be taken in interpretation of the spectra since the near-bandedge PR spectra consists of multiple transitions and the E₁ transition energy is very sensitive to the sample history. Photoreflectance appears to be of limited utility for HgCdTe single layer growth with x<0.4. However, reflectance measurements of the E₁ peak can be used to determine composition in HgCdTe single layers with an accuracy Δx = ±0.01, which can be useful for growth control. A tight binding model was used to calculate the E₁ peak energy as a function of bandgap for HgCdTe and HgTe/CdTe superlattices. Comparisons are made with experimental observations. Surface interdiffusion in HgTe-CdTe superlattices was probed using reflectance measurements.