Evidence for the negative charge state of DX centres in Al_xGa_1-xAs:Si

Abstract

We study here t h e thermally activated capture of electrons on Si-induced impurity states (DX centres) in AI,Ga,.,As ( x = 0.28 and 0.33) after photoionization at low temperature (6. 5-160 K) and under pressure ( C M kbar). We show that the combination of isothermal and thermostimulated experiments under pressure permits u s to state that the capture rates onto the different configurations of the DX centre related to the local environment of the donor atom in the AI,Ga,_,As alloy are not very different from each other, and to unambiguously discriminate between the cases DXO and DX ~. Our results indicate a negatively charged DX ground state

Parameters of multilevel structure of the DX centre in GaAlAs from pressure studies of the Hall effect

“…The emission parameters and the level's separation were the same as used in calculations for x = 0.15, but the level's ladder was pushed down into the gap by taking Eo,, = -120 meV. The simulated PPC recovery dependence n(Q, shown in figure 9, exhibits characteristic step-like structure, which was in fact observed experimentally [5- 7,9]. The evolution ofelectron population on individual DX levels is similar to that found in the x = 0.15 case.…”

“…I t was assumed that these occupancies corresponded approximately to the equilibrium distribution at 140 K, 'frozen' when the sample was cooled under pressure. This means that the energies shown in figure 6 as a function of pressure relate to 140 K. The thermal shift of two levels DX, and DX,, equal to 0.37 meV K-', was found by fitting the model n (7) dependences to the experimental results shown in figure 1 (it was assumed that both levels have the same temperature coefficient). Similar calculations of the level's positions were performed for the positive-Cl (Do) case.…”

“…The measurements were performed with decreasing temperature. After each measurement t h e pressure was released and t h e n ( 7 ) shown in figure 2 three-centre emission dependences given by the integral formula i denotes here the DX level related to the configuration with i = 0-2 AI atoms replacing G a in the vicinity of the relaxed Si centre. For the emission rates e,, we adopted the formula…”

“…The measurements were performed with decreasing temperature. After each measurement t h e pressure was released and t h e n( 7 ) shown in figure 2 measured. Variation of free electron concentration measured at P = 0 during a warm-up of the sample from figure 1.…”

Crystal Orientation Change of Ni Films by Sputtering in Ar-N2 Mixed Gases

“…The results of a recent experiment using deep-level transient spectroscopy on samples co-doped with germanium and silicon showed that DX centres associated with the Ge atoms bound two electrons [18], and Mossbauer measurements on Sndoped GdAs have been interpreted as showing that two or three electrons are localized at each DX centre [19]. Recent interpretations of thermal capture and emission kinetics data of DX centres have been shown to be consistent with a negatively charged DX centre but not ' Local vibrational mode spectroscopy of DX centres with a neutral DX centre [20,21]. Studies of the change in mobility caused by a DX transformation should also help determine if these defects are charged or neutral, but the interpretation ofexisting data has not led to definitive conclusions [22-241.…”