Characterization of MBE Grown Zinc Selenide/gallium Arsenide Heterojunctions by Using Raman Scattering Technique
Abstract
In this study it has been shown that although ZnSe/GaAs structure has several desirable properties, there are also some serious problems to be solved before commercial blue light emitters can be designed and manufactured. By using light scattering technique it was confirmed that there were difficulties in the control of doping levels in ZnSe, that severe interdiffusion across the interface was possible, and that degradation related to heterojunction instability occurred in some cases. These experiments confirmed that light scattering is a powerful technique in the characterization of microstructures: although it has not been fully explored, light scattering is the only technique with which spectrum can be obtained either below or above the fundamental gap of the material, the only technique which is sensitive to both mechanical and electronic characteristics of the scattering medium and the only technique with which the q - dependence of the dielectric function can be studied. This work demonstrated that E_0 gap of ZnSe at room temperature can be determined exactly. The effect of the substrate surface reconstruction on the MBE growth process was studied and the Fermi level positions at ZnSe/GaAs interface in LO-allowed scattering configuration were estimated. Further, the n-type to p -type inversion in the GaAs substrate due to electric field enhanced interdiffusion across the ZnSe/GaAs interface was observed. These topics have been discussed for the first time based on the analysis of the scattering spectra. In addition to the elementary introduction of inelastic light scattering as vibrational spectroscopy and also as intersubband spectroscopy, some misleading concepts and incorrect conclusions in recent publications have been pointed out in this study. In particular, the morphic effect related to the static electric field has been revisited since it is essential for the purpose of heterojunction characterization. The study shows: the effect should be negligible in Raman scattering off resonance, this is in agreement with theoretical prediction and experimental observations. Close to resonance, in LO allowed scattering configuration without polarization analysis, only qualitative information about the band bending can be obtained. On the other hand, in the case of near resonance and in the LO-forbidden scattering configuration, quantitative information about the band bending can be extracted from the light scattering spectrum.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- January 1992
- Bibcode:
- 1992PhDT.......132L
- Keywords:
-
- ZINC SELENIDE;
- GALLIUM ARSENIDE;
- Physics: Condensed Matter; Physics: Optics