High spatial resolution photoluminescence studies of dislocations in Si-doped, liquid-encapsulated Czochralski GaAs

Abstract

High spatial resolution photoluminescence experiments were performed on Si-doped, liquid-encapsulated Czochralski-grown GaAs. Typical defects investigated were grown-in dislocations surrounded by impurity atmospheres (G) and grown-in dislocations moved by thermal stresses during the post-growth cooling period leaving behind a glide trace (GS). Diluted Sirtl-like etching with the use of light was performed to localize the defects, which showed up as hillocks with a small summit at the dislocation outcrop. The luminescence experiments were carried out in a helium bath cryostat at 4.2 K using a newly developed focusing and translation mechanism, mounted inside the cryostat. A spatial resolution of ≊1 μm could thus be obtained. Grown-in dislocations, starting and ending points of GS dislocations, as well as their glide traces were all found to yield lower luminescence intensities than the crystal matrix. Moreover, a relative enhancement of the (D0,h) transitions with SiGa as a donor compared to the (e,A0) transitions with SiAs as an acceptor was observed at isolated grown-in dislocations and starting points of GS dislocations. Glide traces and ending points of GS dislocations, however, at which the photoluminescence intensity was also significantly lower than at the crystal matrix, did not show this enhancement. The results are explained on the base of a relatively high concentration of nonradiative deep centers at all of the above-mentioned defects, and a high concentration of shallow donors at grown-in dislocations and starting points of GS dislocations. The distinction found between different defects with regard to the impurity incorporation is explained in terms of the thermal history of the crystal.