Microstructural Changes in MBE Growth of Low-Temperature Gallium Arsenide Observed by in Situ Ellipsometry
An ellipsometer system has been developed for in-situ monitoring of III-V semiconductor growth using molecular beam epitaxy. Included as part of this work, a software package was developed for the calibration, acquisition, display and modeling of ellipsometry data. This calibration software addresses the arbitrary orientations of the analyzer and polarizer components that are present in the mounting of the ellipsometer on the MBE system. In addition, this package calculated the trajectory followed during the growth of a homogeneous film. The materials used in the modeling are restricted to either an isotropic material or a uniaxial material with the optic axis oriented normal to the surface. External to the real-time software package, a general scheme for the analysis of ellipsometric data was developed using MATLAB. The ellipsometer described above was utilized to reproducibly grow and monitor the growth of low temperature (LT) GaAs films in-situ. In particular the capping of GaAs(001) with As was monitored and a method was developed which could be used to characterize the growth temperature of GaAs in the vicinity of 190^circ C. This method utilizes the temperature for the formation of a thin film of As on GaAs(001). Using this technique to set the growth conditions, LT-GaAs films were grown and monitored in real-time with the ellipsometer and characterized ex-situ with X-ray diffraction (XRD) and transmission electron microscopy (TEM.) The ellipsometry data allowed for the observation of the formation of the epitaxial LT-GaAs film and a subsequent region of changing dielectric properties. These results are correlated with observation in double crystal X-ray diffraction (DXRD) and TEM analysis, showing that the refractive index can be used to indicate the composition of the LT-GaAs films and that the ellipsometer can observe the breakdown in the crystallinity of the LT-GaAs layers.
- Pub Date:
- January 1995
- THIN FILMS;
- Engineering: Materials Science; Physics: Condensed Matter; Engineering: Electronics and Electrical