ODMR investigations of DX centres in Sn- and Si-doped AlxGa1-xAs
In a thick (100 mu m) Sn-doped Al0.35Ga0.65As layer and an 11 mu m Si-doped Al0.41Ga0.59As layer the magnetic circular dichroism (MCDA) of the optical absorption, the optically detected electron spin resonance (ODEPR) and the photoconductivity (only in the Sn layer) have been measured simultaneously. All signals appear together after the photoionization of the DX centre and are directly correlated to each other. The ODEPR spectra measured in the MCDA bands show the hyperfine doublets due to the magnetic 117Sn and 119Sn isotopes (I=1/2) in Sn-doped samples and an ODEPR line (I=0) in Si-doped layers. The 4.7% abundant 29Si (I=1/2) isotopes could not be observed. The authors show that the MCDA is due to a neutral (Si0, Sn0) donor, a deep level which is stable at 1.6 K in the dark. This DX0 state needs thermal energy or light to capture an electron to form the negative-U DX- ground state which contains one donor dopant in a large lattice configuration.