Real-time monitoring and control during MOVPE growth of CdTe using multiwavelength ellipsometry

New multi-wavelength in-situ ellipsometer hardware and data analysis software are described. The hardware can simultaneously acquire accurate ellipsometric data at 12 wavelengths in less than 1 s, is simple and compact and is well suited for in-situ monitoring. The data analysis software implements a “virtual interface” approach to determine in real time the characteristics (growth rate and composition) of the near-surface region of the film. These new tools were used to study the metal-organic vapor phase epitaxy (MOVPE) growth of CdTe on GaAs. From a post-deposition analysis of the in-situ data, dielectric constants of CdTe at growth temperature were obtained. Non-uniformity in the CdTe film thickness, and film nucleation during the initial stages of growth, were also observed in the post-deposition analysis. The determined CdTe dielectric constants were utilized in subsequent depositions to determine the growth rate of a CdTe film in real time. Feedback control of the CdTe growth rate was effected by connecting an analog control voltage line from the data acquisition/analysis computer to the Cd mass flow controller.