Anisotropic electric-field-enhanced electron emission from deep-level defects in GaAs

Abstract

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.

Ion-Implantation Control of Ferromagnetism in (Ga,Mn)As Epitaxial Layers

“…24 It forms an acceptor level located 0.58 eV below the conduction-band edge, which corresponds to the deep-level electron trap labeled EL3, commonly observed with deep-level transient spectroscopy in n-type GaAs crystals; see Ref. 25 for a very recent review of the defect properties. As a consequence of the negative-U property, the O As defect behaves as a deep donor in p-type crystals, thus giving rise to additional compensation of Mn Ga acceptors in the oxygenimplanted (Ga,Mn)As layers.…”

Extended deep‐level defects in MBE‐grown p‐type CdTe layers

“…7, was fitted to Eq. (4) giving the τ 1 value of 1.0×10 -14 s, which indicates a strong coupling of the defect to the lattice vibronic modes [11].…”

“…where the minus sign corresponds to the adiabatic potential structures of on-site (moderate lattice relaxation) and the plus sign corresponds to the autolocalized (very large lattice relaxation resulting in metastable states) centres. τ is the tunnelling time through the barrier, τ 1 is the time constant proportional to the inverse local defect vibration frequency and α is a fitting parameter [11]. Measurements of the electric-field dependences of hole emission rates, performed for the H5 trap at various temperatures, shown in Fig.…”

Phonon‐assisted tunnel emission of holes from the double donor level of the EL2 defect

“…Fitting that equation to the τ 2 values requires an additional fitting parameter α (close to unity) and the plus sign in Eq. , according to the following relation : which gives the τ 1 value equal to 2.9 × 10 −14 s. This value of τ 1 time constant is an order of magnitude larger than the τ 1 values determined previously for two electron traps, called EL3 and EL5, associated with defects of lowered local symmetry in n‐type GaAs crystals and for the DX centre in Te‐doped n‐type AlGaAs ternary compound . On the other hand, two to three times larger τ 1 values, of above 5 × 10 −14 s, have been obtained for deep‐level traps associated with substitutional Au and Hg impurities in p‐type Ge and the vacancy‐oxygen complexes in n‐type Ge .…”