DX-like properties of theEL6defect family in GaAs

Abstract

Capacitance-voltage characterization at different temperatures and emission and capture deep-level transient spectroscopy carried out on undoped n-type GaAs lend strong confirmation to the recent suggestion that the EL6 defect arises from a center that is DX-like in nature. The evidence comes from the observation of an anomalous filling pulse duration dependence of the peak intensities of three to four different EL6 sublevels, similar to that recently found for the DX center in Al x Ga 1Ϫx As and attributed to the charge redistribution. In addition, capture transients reveal large capture barriers ͑0.2-0.3 eV͒, which are typical of a defect undergoing large lattice relaxation into a deep-lying state. These observations indicate that the EL6 defect center comprises of a center with three to four slightly different ground-state configurations, each one of which forms as a result of some bond-breaking atomic displacement on capture of a second electron at the defect site. The significance of this in understanding the microstructure for the EL6 center is briefly discussed.

Simple intrinsic defects in gallium arsenide

“…The EL2 defect seen in arsenic-rich native GaAs is observed to be double donor [37][38][39]51]. Our computed midgap As Ga (0/+) donor state, at 0.80-0.81 eV below the CB, is consistent with experimental observations for the EL2(0/+) level, ranging from 0.74 to 0.83 eV below the CB edge [37][38][39][51][52][53][54][55][56][57][58]. We reiterate that the DFT supercell calculations can only unambiguously calculate the positions of the defect levels with respect to one another, the position of a CB (or VB) edge with respect to a defect level cannot be directly computed.…”

“…No other intrinsic defects have levels this high in the band gap. The DX-like properties of the EL6 center [58] can be explained by the global bistability in v As , as it shifts between the simple v As vacancy and the v * As (Ga As -v Ga nearest neighbor pair) [91]. The identification of the E3 center with the v As justifies treating the Ga As -v Ga pair as a distorted manifestation of the simple As vacancy, and including it in computing levels for v As as the v *…”

TheE1–E2 center in gallium arsenide is the divacancy

“…The EL6 emission exhibits a large Franck-Condon factor, 0.6 eV, indicating this transition is associated with a large lattice relaxation [22]. It was later shown that the EL6 was but one of several emission peaks from a single defect: the intensities could be shifted between the EL5-EL6-EL7 family of levels by varying the filling pulse length in DLTS (deep-level transient spectroscopy), indicating a single DX-like center was responsible for these levels [25]. The predicted −U v As (3 − /1−) has a DXlike lattice relaxation, this transition involves a Ga atom hopping between two sites, from v As into v * As , as illustrated in figure 1(c).…”

“…The E3 center is known to be a primary defect of displacement damage-it must be an intrinsic defect-and is an important recombination center in GaAs [21]. The E3/EL6 energy level is reported to be 0.27-0.38 eV below the conduction band edge [3,[20][21][22][23][24][25]. The only viable candidate in the computed survey of intrinsic defect levels is the −U v As (3 − /1−) transition, at roughly −0.3 eV in LDA (−0.35 eV in PBE), where this defect will emit two electrons midway between the (3−/2−) and (2−/1−) energy levels.…”

Deep centres in bulk MOCVD n‐type hexagonal GaN thin films and near their interface

“…Arrhenius diagrams can be derived from the analysis of these HR-ITS spectra at various temperatures and would result in ionisation energies and capture cross sections in the same ranges as previously determined by FT-ITS [10]. Such multiple deep levels are rather common in III-V semiconductors but has been correctly analysed only for about ten years [11,12]. These traps are found only in samples where doping or contamination by silicon occurred.…”