Study of microdefects and their distribution in dislocation-free Si-doped HB GaAs by X-ray diffuse scattering on triple-crystal diffractometer

Abstract

Microdefects in dislocation-free Si-doped (n = (1–3) × 10 18 cm -3) HB GaAs crystals were studied by X-ray diffuse scattering measured with the help of a triple-crystal diffractometer. The intensity of the diffuse scattering as well as the isointensity contours around different reciprocal lattice points were analysed. A comparison of the measured isointensity contours with the theoretically calculated ones showed that the microdefects detected are interstitial dislocation loops with the Burgers vectors b = 1 2 <110 #3862;; lying in the planes #38;{110} and {111}. The mean radius of the dislocation loops R 0 was determined using the wave vector q 0 alpha; R -1 0 corresponding to the transmition point where the Huang diffuse scattering I( q) alpha q -2 ( q < q 0) changed to the asymptotic scattering I( q) alpha q -4 ( q #62 q 0). The analysis of a D-shaped cross-sectional (111) wafer cut from the end part of the HB ingot showed that R 0 changed smoothly along the [ 2 11] symmetry axis of the wafer. The highly inhomogeneous “new-moon”-like distribution of the non-dislocational etch-pits was also obtained. The maximal loop radius obtained at the edges of the wafer, R 0 = 1 μm, corresponds to the wafer area enriched with etch-pits and the minimal one, R 0 = 0.3 μm, corresponds to the bound of the new-moon-like area denuded from etch-pits. Microdefects of a new type were detected in the denuded area. These microdefects consist of nuclei, 0.1 μm in radius, and an extended atmosphere of interstitials. The minimal microdefect radius in the centre of the wafer corresponds to the maximum local value of the lattice parameter a = 5.655380 A ̊ , and the minimum local value a = 5.65372 A ̊ was obtained at the wafer edges enriched with microdefect-related etch-pits. Absolute X-ray diffuse intensity measurements were used for microdefect concentration determination. Normalization of I( q) was based on the comparison of the Huang intensity with the thermal diffuse scattering intensity which is predominant for the wave vector q å R -1 0. The microdefect concentration determined in this way appeared to be 4 × 10 9 cm -3 at the edges of the wafer and 4 × 10 11 cm -3 at the centre of the new-moon-like etch-pit denuded zone. The number of interstitial atoms forming dislocation loops is shown to be the same across the area of the wafer and equal to 10 16 cm -3.