FORMATION OF STRAIN-FREE GAAS-ON-SI STRUCTURES BY ANNEALING UNDER ULTRAHIGH PRESSURE

Theoretical and experimental discussions on a novel method to solve the thermal mismatch problem in heteroepitaxial growth have been reviewed. It has been predicted theoretically for structures such as Ge/Si and GaAs/Si that the difference in thermal expansion coefficients can be compensated for by the elastic strain generated by hydrostatic pressure. This theoretical prediction has been verified experimentally using GaAs-on-Si structures, in which the structures are formed by metalorganic chemical vapor deposition and subsequently annealed under ultrahigh pressure. It has been found that for annealing at pressures up to 2.1 GPa, the strain in GaAs films decreases linearly with increasing pressure and becomes zero at a pressure of around 1.9 GPa. It has also been found that the strain depends weakly on the annealing temperature, which ranged from 300 to 500 degrees C. Concerning the crystalline quality of the annealed GaAs films, a slight increase in the minimum channeling yield in Rutherford backscattering spectrometry has been observed in the samples with broad-area GaAs films. It has been found, however, that degradation in the crystalline quality can be avoided by etching the GaAs films in a pattern of stripes 10 mu m wide.