A STUDY OF TRANSIENT CAPACITANCE OF GOLD ACCEPTOR ENERGY LEVEL IN SILICON UNDER UNIAXIAL STRESS

Abstract

Using the method of transient capacitance at constant temperature, the shift of gold acceptor energy level in silicon under 〈100〉,〈110〉,〈111〉 uniaxial press has been studied. Considering the split of conduction band caused by uniaxial stress, a formula for electron emission rate from deep center to conduction band has been derived. With this formula and experimental data of emission rate and reported tangential deformation potential constant Ξu ,the active energy of gold acceptor under various uniaxial stress has been determined. In the range of experimental stress (0-9 kbar), a linear dependence of active energy on stress has been found. When uniaxial presses are parallel to 〈110〉,〈111〉 crystal orientations, the proportionality constants are α=-3.2±0.6 meV/kbar, α=-0.3±0.6 meV/kbar respectively. When uniaxial press is parallel to 〈100〉 crystal orientation and if we take Ξu = 9.2 eV, α= -5.8± 0.8 meV/kbar, or if Ξu =11.4 eV, α=-5.3± 0.8 meV/kbar. The changes of active energy are strongly anis-otropic. Further more, we have determined the shift coefficients of gold acceptor level in the presence of uniaxial stress relative to the bottom of conduction band in the absence of uniaxial stress. When Ξu=9.2 eV, the coefficients are S=-1.3±0.8 meV/kbar, S=0.7±0.6 meV/kbar, S=-0.7±0.6 meV/kbar respectively, when Ξu=11.4 eV, the values are S= - 3.5± 0.8 meV/kbar, S = 0.0±0.6 meV/kbar, S=- 1.0±0.6 meV/kbar. Deviations among three coefficients of each group are larger than uncertainty of experiments. Thus, the possibility that gold centers in silicon have cubic symmetry and at the same time both negatively charged and neutral gold centers have nondegenerate basic states is quite small.