DIRECT EVIDENCE FOR THE NEGATIVE-U PROPERTY OF THE DX-CENTER AS STUDIED BY HYDROSTATIC-PRESSURE EXPERIMENTS ON GAAS SIMULTANEOUSLY DOPED WITH GE AND SI

DX centers in GaAs codoped with Ge and Si have been investigated under a hydrostatic pressure, where Ge acts as a DX center, and Si as a shallow donor. It is demonstrated that the number of electrons trapped by the Ge DX center at 22 kbar increases with Si concentration and tends to saturate at a certain value. The behavior substantiates the negative-U model of the DX center, where two electrons are bound to a DX center. © 1990 The Japan Society of Applied Physics.