First Principle Calculation and Photoluminescence Spectroscopy of the DX Center

Abstract

In order to resolve the controversy (large lattice relaxation or small lattice relaxation?) regarding the origin of DX centers theoretically, ab initio self-consistent pseudopotential method has been applied to 64-atom super cell for donor-doped GaAs under high pressure and donor-doped AlxGa1-xAs alloys. The total energy and force calculations predict that an almost unrelaxed donor atom with Td symmetry has the most stable configuration. On the contrary, a negatively charged donor with broken-bond configuration gives a metastable state and not the ground state even under hydrostatic pressures up to 60 kbar. Furthermore, to resolve this controversy experimentally, we have performed photoluminescence (PL) spectroscopy on Si-doped AlxGa1-xAs (x=0.32-0.4). We have observed for the first time band-edge PL for below-gap photoexcitation in these systems at low temperatures (< 50 K). This result strongly suggests the validity of the present theoretical predictions.