Uniaxial stress dependence of the ” EL2 ” and ” EL3 ” deep levels in bulk GaAs

2014 We present uniaxial stress measurements performed on the activation energies of both the deep EL2 center in GaAs (820 meV), often called « O » center, and the EL3 electronic trap (600 meV). The EL2 level is found to separate from the conduction band at a rate of (1.1 + 0.6) meV/kbar for uniaxial stress in the (100) direction and (0.8 ± 0.5) meV/kbar for uniaxial stress in the (111) direction. Both values are consistent with the pressure coefficient reported under hydrostatic conditions. The second level (EL3) exhibits more important stress dependences : (1.8 ± 0.3) meV/kbar under (100) and (2.8 ± 0.4) meV/kbar under (111) compressions, respectively. Revue Phys. Appl. 15 (1980) 1517-1520 OCTOBRE 198 Classification Physics Abstracts 71.55Fr 73.30Fy 71.70Ej Introduction. In cubic compounds, the association of shallow impurity states with satellite minima of the conduction band has long been established [1-3]. In this case, the corresponding energy levels closely follow a given minimum of the conduction band versus external perturbations, like, for instance, hydrostatic pressure [1, 2] or a change in temperature [3]. Concerning deeper impurity states, the situation is more complex [4]. The general assumption in this case is that they correspond with a close admixture of r, L and X contributions ; the shorter the extent of the potential in real space, the larger the admixture in k-space. Depending on the amount of admixture, one expects to find pressure coefficients in GaAs for the thermal ionisation energy of impurity ranging between the limiting values : zero (for pure 03931 like state) and 14.1 meV/kbar (for X,-like state). In good agreement with these qualitative arguments, recent data concerning electron irradiation in GaAs [5] report for different levels, lying at 0.18, 0.31 and 0.71 eV below the minimum of the conduction band, the pressure coefficients : 8.8, 14 and 11 meV/kbar respectively. Even more interesting are the data collected [6] for the electronic trap located 210 meV below the bottom of the conduction band in GaAs. lt shifts with a slope 11.6 meV/kbar under hydrostatic pressure but exhibits shear dependences : 4.0 meV/kbar under (111) stress and 3.5 meV/kbar under (100) stress. The difference between the two uniaxial results is too large to be associated with experimental uncertainties (according to the authors of Ref. [6]) and confirms the predominent X-like character of this bound state. Concerning now the deep oxygen « EL2 » center which is most commonly found in GaAs (El = 820 meV), two reports of the associated pressure dependence have been given [7, 8]. Both concern hydrostatic conditions, but White et al. [7], using a photocapacitance technique report (1.2 ± 1 ) meV/kbar while Zylberstein et al. [8], using a transient capacitance technique, report (3.8 ± 0.3) meV/kbar. The purpose of this paper is twofold. First obtain Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:0198000150100151700