Stoichiometry Control of Compound Semiconductor Crystals

Most important factor to be controlled in compound semiconductor crystals is the deviation from the stoichiometric composition. Electrical, optical and crystallographic evaluation are applied to the GaAs samples prepared by annealing under controlled As vapor pressure. It is shown that the crystal imperfection and the deviation from the stoichiometric composition are reduced to be minimum under a specific As vapor pressure (optimum As vapor pressure; PAs,opt). PAs,opt is obtained to be similar regardless of the difference of dopant species, dopant concentration and conductivity type. Optimum vapor pressure is also obtained in other compound semiconductor crystals including GaP etc. The deviation from the stoichiometric composition affects the amphoteric manner of Si in GaAs. Vapor pressure control is also applied to the liquid phase epitaxy (LPE) in combination with the temperature difference method (TDM-CVP), and almost the same results are obtained. Temperature dependence of the optimum vapor pressure is almost the same both in annealing and LPE experiments. It confirms that the applying vapor pressure controls the composition of segregated crystals directly through the solution in LPE. Various methods including Rutherford backscattering (RBS) technique are applied to investigate the excess As atom-related defects in GaAs. The experimental results of crystal weight and X-ray anomalous transmission intensity measurements directly suggest the existence of interstitial As atoms. The RBS measurements with glazing exit angle configuration show the existence of the interstitial As atoms in As+-implanted GaAs, and clarify the stable interstitial sites to be split and relaxed- bond center (r-BC) interstitialcy. Formation energy of excess As atom-related defects is determined to be 0.9–1.16eV by both the lattice constant measurements and the PHCAP measurements independently.