ANALYSIS OF THE VACANCY-INTERSTITIAL MODEL OF DX CENTERS

I describe the vacancy-interstitial model of DX centers, in which the substitutional donor atoms relax toward interstitial sites when they capture electrons. This appears to be the only known model of DX centers which can account for the structure observed by Mooney et al. in DLTS spectra of dilute Al(x)Ga1-xAs alloys. By comparing its predictions with the DLTS and Hall data from Al(x)Ga1-xAs alloys of low Al content one can establish values for many of the relevant parameters, such as the enthalpies and entropies (degeneracies) associated with sites surrounded by differing numbers of Al atoms. The data also show that the distribution of donor configurations among the four available neighboring interstitial sites does not attain thermal equilibrium among states of differing energies before being released, although transitions (through tunneling) among states of equal energy may be possible. The model is seen to be consistent with those treated theoretically by Chadi and Chang for DX and by Dabrowski and Scheffler for EL2 centers.