Acceptor-Like Level of the EL2 Defect in its Metastable Configuration

Abstract

This paper presents for the first time the evident experimental confirmation that ΕL2 defect, while being in its metastable configuration, traps under hydrostatic pressure an additional electron, i.e. the acceptor-like ( E L 2 * )°/ -l e v e l e n t e r s t h e e n e r g y g a p u n d e r p r e s s u r e . W e p r o p o s e t h a t i n n -G a A s t h e ΕL2 thermal recovery takes always place via the (ΕL2') state.PACS numbers:71.55.Eq, 78.50.GeOur recent experimental results showed that under pressure of p > 0.3 GPa the metastable configuration of the EL2 defect in GaAs became optically sensitive and a very efficient pure optical recovery process was observed [1]. We suggested that these facts could be related to the acceptor-like level of the metastable EL2 -(EL2*)0/ -, entering the gap under pressure. In this work we present the experimental evidence of the above suggestion. We investigated two n-GaAs samples: #5Β with n300Κ = 1.2 x 1016 cm-3, ΝEL2 = 2.7 x 101 6 c m -3 a n d # 1 5 C w i t h n300κ = 3.2 x 10 16 cm-3 , ΝΕL2 = 1.3 x 1016 cm-3. Clear manifestation of the (EL2*)°/ -level was observed in electrical (conductivity and DLTS) measurements.At temperatures Τ < Τ (where Τ -temperature at which EL2 thermally recovers) and sufficiently high pressure (p > 0.3 GPa) during subsequent optical quenching and optical recovery processes strong persistent changes of the electrical conductivity were observed. This was the consequence of the trapping and releasing of the electrons by EL2 optically transferred between its normal (EL20) and This worlds supported by CPBP 01.05 Program of the Polish Ministry of National Education (129)

Absolute pressure dependence of the second ionization level of EL2 in GaAs

“…Conflicting results, however, have been reported recently for the pressure dependence of the electron capture barrier of EL2(o/+), with one group reporting no pressure dependence of the barrier [18] and another group finding a large pressure dependence [19] of dEb/dp =- Therefore we would find the pressure coefficients for the equilibrium excitation energy, ET, of the first and second ionization levels of EL2 to be very similar.…”

“…One can compare these data with the results of theoretical calculations of pressure dependence of energy levels associated with native defects in GaAs [19] It is predicted in these calculations that the pressure derivatives of energy levels of native defects involving the Ga-site depend only very weakly on the location of the level in the band gap. In particular, for the ASGa antisite defect the energy levels with A1 symmetry located at -Ev+0.75 and at Ev+0.57 are predicted to have pressure derivatives of -35 meV GPa-1 and 32 meV GPa-1, respectively.…”

Nonlinear Coupling of Oscillatory Modes in Current Flow in Semi-Insulating GaAs

“…We suspect that domain motion is related to capturing of the conduction band electrons by EL2. This comes from the fact that the electric field required for the domain creation is high enough to enable field enhanced trapping of electrons by EL2 [8][9][10] and that measurements of the frequency of the domain oscillations as a function\ of the temperature showed an activation dependence with an energy equal to 0.06 eV, the value which is to a good accuracy equal to the height of the barrier for conduction band electron capture by EL2 [11]. The other mode is created by photocurrent oscillations caused by absorption of 0.98 μm light with modulated intensity.…”

Electron Temperature in Semi-Insulating GaAs for Low Electric Fields

“…The capture rate c n is given by the formula cn = υ t hσ , where υth is the thermal velocity of electrons and σ is the capture cross-section. To describe the dependence of cn on the electric field we express υth and σ by a field dependent electron temperature Te: υth = (3kTe/m*) 1 /2 and σ = σ exp(-Eb/kT), where Te = T(1 + αΕ2 ) [10], m* is the free electron effective mass and Eb = 0.063 eV is the height of the configurational barrier of the EL2 [11]. In other words, we assume that the free electron distribution is Maxwellian, but characterized by Te instead of T. We fit the cn on Ε dependence using the above formulae taking σ and α as the fitting parameters.…”