Characterization of lattice strain from DX centers and persistent photocarriers in GaAlAs

Abstract

We discuss the results of high resolution, low temperature X-ray diffraction measurements used to determine the lattice strain caused by electron emission from Sn- and Si-related DX centers in Ga 1 − x Al x As. DX centers are deep levels associated with donors in various III–V semiconductors, and they are responsible for persistent photoconductivity and other unusual electrical and optical properties of these materials. Although DX centers have been extensively studied for more than a decade, information is still needed about the atomic arrangements that comprise DX centers for various donor and host systems. Our lattice strain measurements show that there is lattice expansion attributable to local bonding changes that occur when the DX centers are emptied. This result is important in testing proposed structural models for the DX center, and it can be used to rule out a proposal that symmetric breathing-mode relaxation is responsible for a DX − state for Sn-doped Ga 1 − x Al x As. The theoretical proposal by Chadi ( Phys. Rev. B, 46 (1992) 6777) requires an inward relaxation when a Sn-related DX center is emptied, but our experiments show an outward relaxation.