LATTICE STRAIN FROM SUBSTITUTIONAL GA AND FROM HOLES IN HEAVILY DOPED SI-GA

The average lattice strain per Ga atom with respect to pure silicon, beta(total) = DELTA-a/aN(Ga) = +(0.9 +/- 0.1) x 10(-24) cm3, for heavily doped Si:Ga was measured by high-resolution x-ray diffraction. This strain includes effects of both substitutional Ga atoms in the lattice and doping-related holes in the valence band. The local "size-effect" lattice strain around substitutional Ga atoms, which is not expected to be affected significantly by valence-band holes, was determined from the Ga-to-Si nearest-neighbor distance measured using extended x-ray-absorption fine structure (EXAFS). This distance, r(NN) = 2.41 +/- 0.02 angstrom, is 0.06 angstrom larger than the usual Si-to-Si nearest-neighbor distance and was used to calculate the size-effect contribution per Ga atom to the average lattice strain, beta(size) = (1.2 +/- 0.3) x 10(-24) cm3. This value was subtracted from the overall lattice strain beta(total) to determine the lattice strain per valence-band hole, beta(h) = -(0.3 +/- 0.3) x 10(-24) cm3, and the hydrostatic deformation potential for the valence-band edge in silicon, a(upsilon) = -0.5 +/- 0.5 eV. These results were obtained from Si:Ga samples prepared by liquid-phase epitaxy. They were characterized by Rutherford backscattering, ion channeling, electron microscopy, and resistivity measurements, as well as by x-ray diffraction and EXAFS. The samples were of excellent crystal quality, with uniform Ga concentrations of 1.0 and 1.5 x 10(20) cm-3, with substitutional fractions greater than 95% and similar electrical resistivities of 2 x 10(-3) OMEGA cm.