Group II Cubic Fluorides as Dielectrics for III-V Compound Semiconductors.

摘要

The epitaxial growth of lattice matched Ca(x)Sr(1-x)F2/Gallium Arsenide and GaAs/Ca(x)Sr(1-x)F2 heterojunctions by molecular beam epitaxy is investigated. These heterojunctions are potential candidates for realizing opto-electronic devices involving III-V Compound Semiconductors. The composition x=0.5 is chosen to minimize the lattice mismatch at room and growth temperatures. The fabrication of the layers involves the sequential growth of GaAs wafers of a GaAs buffer layer, a 2000-3000A Ca5SrF3 layer, and a top 500-3000A GaAs layer. The growth along the (100), (111), (511) and (711) orientations is investigated. Optimum growth temperatures range from 500 C to 550 C for the fluorides, and 550 C to 600 C for the GaAs. The orientation of the substrate is conserved throughout the three epitaxial layers. The bulk crystallinity, studied with ion scattering, is found to be excellent in the GaAs buffer layer, fair to good in the fluoride layer, and poor to fair in the top GaAs layer. The high Miller-index GaAs surfaces ((511), (711)) exhibit a regular stepped structure ((100) terraces) which contributes to the reduction of anti-phase disorder in the fluoride layer. It is also found that the (511) orientation is favorable for the growth of the top GaAs layer. Rough morphology and facetting at fluoride surfaces are identified as the main problems for the growth of high quality top GaAs layers. Post-growth thermal treatments and electron-beam exposure will be investigated as potential solutions. Keywords: Semiconductor/insulator/semiconductor heterojunctions; Calcium compounds; Strontium compounds; Fluorides. (aw)