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

Theoretical and experimental discussions on a novel method to solve th e thermal mismatch problem in heteroepitaxial growth have been reviewe d. It has been predicted theoretically for structures such as Ge/Si an d GaAs/Si that the difference in thermal expansion coefficients can be compensated for by the elastic strain generated by hydrostatic pressu re. This theoretical prediction has been verified experimentally using GaAs-on-Si structures, in which the structures are formed by metalorg anic chemical vapor deposition and subsequently annealed under ultrahi gh pressure. It has been found that for annealing at pressures up to 2 .1 GPa, the strain in GaAs films decreases linearly with increasing pr essure and becomes zero at a pressure of around 1.9 GPa. It has also b een found that the strain depends weakly on the annealing temperature, which ranged from 300 to 500 degrees C. Concerning the crystalline qu ality of the annealed GaAs films, a slight increase in the minimum cha nneling yield in Rutherford backscattering spectrometry has been obser ved in the samples with broad-area GaAs films. It has been found, howe ver, that degradation in the crystalline quality can be avoided by etc hing the GaAs films in a pattern of stripes 10 mu m wide.