Electroreflectance of germanium

The band structure of germanium in the energy region .7 eV to 5 eV was investigated using the electroreflectance (ER) technique. Several transitions were detected in this energy range and in almost all cases, the associated critical points were identified as to their type and origin in k-space. At the direct edge (r~ r7 transitions at .79 eV), interference between the degenerate light and heavy hole band contributions to the lineshape was observed and a good fit to the sum of two one-electron lineshapes for a 3-dimensional M critical point was obtained. A good fit to the 3-D M theory was also obtained for the spin orbit split structure (r7 ~ r7 transitions at 1.08 eV) and was used as a means of determining the electric field. A doublet structure at 2.1-2.3 eV was shown to agree extremely well with the 2-dimensional M critical point theory. In addition, effects due to band-filling were observed when the energy bands were bent into accumulation. These results indicate that the transitions responsible for this structure occur over an extended region of the Brillouin zone, including the L-point. Structure was also observed near 3 eV and 4 eV but the large amount of lifetime broadening prevented any detailed quantitative analysis. The 4 eV structure, however, was characteristic of a single 3-D M1-transverse critical point and the broadening of this structure was estimated to be 120 meV. A set of experimental conditions necessary for making reliable ER measurements which agree with the uniform-field, one-electron theory, was developed and used throughout the experiment. These included: (1) modulation from the flat-band condition, (2) the use of high fields to minimize many-body effects, and (3) the use of uniform fields by proper choice of sample doping levels and modulation conditions.U of I Onlydissertatio