Strongly anisotropic electric-field enhancements of the thermal emission rates of electrons from the EL3 and EL5 deep-level defects in n-type GaAs crystal have been revealed with the double-correlation deep-level transient spectroscopy. The results, analysed by taking into account both the Poole-Frenkel and phonon-assisted tunnel effects, evidence a strong coupling of the defects to the lattice vibronic modes. The defect potential anisotropy of EL3 is consistent with the defect identification as an off-centre substitutional oxygen on the arsenic site. The revealed surprising break-down of the emission-rate enhancement, for the electric field applied along the 1 0 0 crystallographic direction, is interpreted as resulting from a possible reorientation of the EL3 defect, owing to a jump of the oxygen ion into a neighbouring lattice site, driven by a strong electric field. On the other hand, a close pair divacancy complex is suggested to be responsible for the EL5 defect.

We present results of deep-level transient spectroscopy investigations of defects in a GaN-based heterostructure of a blue-violet laser diode, grown by plasma-assisted molecular beam epitaxy on a bulk GaN substrate. Three majority-carrier traps, T1 at E C − 0.28 eV, T2 at E C − 0.60 eV, and T3 at EV + 0.33 eV, were revealed in deep-level transient spectra measured under reverse-bias conditions. On the other hand, deep-level transient spectroscopy measurements performed under injection conditions, revealed one minority--carrier trap, T4, with the activation energy of 0.20 eV. The three majority--carrier traps were revealed in the spectra measured under different reverse--bias conditions, suggesting that they are present in various parts of the laser--diode heterostructure. In addition, these traps represent different charge--carrier capture behaviours. The T1 trap, which exhibits logarithmic capture kinetics, is tentatively attributed to electron states of dislocations in the n-type wave-guiding layer of the structure. In contrast, the T2, T3, and T4 traps display exponential capture kinetics and are assigned to point defects.

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