HALL-EFFECT, PHOTOLUMINESCENCE AND DLTS INVESTIGATION OF THE DX CENTER IN ALGAAS

The DX centre was observed on MOCVD-grown unintentionally doped Al 0.3Ga0.7As by means of the Hall effect involving persistent photoconductivity (PPC), temperature-dependent photoluminescence (PL) and deep-level transient spectroscopy (DLTS). The ionisation energies of the hydrogen-like shallow donor (EaD=23 meV) and of the deep donor (Eadd=120 meV) with regard to the Gamma minimum were observed simultaneously by PL investigations at T=75 K. The value E add observed from the difference between the DLTS emission and capture barrier agrees excellently with that found by PL studies. The PL emission due to the transition involving the occupied DX centre was observed in a narrow temperature range (70<or=T<or=140 K). The population of the DX centre by thermally activated electrons which surmount the occupation barrier at these temperatures is indicated by the drop of the PPC and the DLTS capture studies. For the capture activation energy of the deep donor a value of 240 meV is obtained.