Thermal Emission Rates Of Holes Research Articles

Surface acceptor states in MBE-grown CdTe layers

A deep-level hole trap associated with surface defect states has been revealed with deep-level transient spectroscopy investigations of metal-semiconductor junctions fabricated on nitrogen doped p-type CdTe layers grown by the molecular-beam epitaxy technique. The trap displayed the hole-emission activation energy of 0.33 eV and the logarithmic capture kinetics indicating its relation to extended defect states at the metal-semiconductor interface. Strong electric-field-induced enhancement of the thermal emission rate of holes from the trap has been attributed to the phonon-assisted tunneling effect from defect states involving very large lattice relaxation around the defect and metastability of its occupied state. Passivation with ammonium sulfide of the CdTe surface, prior to metallization, results in a significant decrease in the trap density. It also results in a distinct reduction in the width of the surface-acceptor-state-induced hysteresis loops in the capacitance vs. voltage characteristics of the metal-semiconductor junctions.

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

Strong electric‐field‐induced enhancement of the thermal emission rate of holes from the doubly ionised charge state of the ΕL2 defect was revealed with the double‐correlation deep‐level transient spectroscopy in p‐type GaAs crystals of various crystallographic orientations. The observed enhancement, by over four orders of magnitude of the emission rate, was analysed in a model of phonon‐assisted tunnel ionisation. Similar dependences of the hole‐emission rate on the electric‐field intensity received for the electric‐field directions parallel to three main crystallographic axes evidence for tetrahedral symmetry of the defect, which is consistent with its identification as the isolated arsenic antisite defect.

The electrically active centers in oxygen-implanted silicon

Electrically active centers have been firstly studied by the capacitance transient spectroscopy technique in p-Cz-Si implanted with oxygen ions and annealed in a chlorine-containing atmosphere. The temperature dependences of the thermal emission rates of holes from the levels to the valence band were measured and the influence of the annealing conditions on the level concentrations were studied. The deep and shallow levels revealed in the samples with dislocation related luminescence are characterized by similar level parameters to those observed in samples containing extended defects and performed by different techniques (deformation, formation of oxygen precipitates and direct bonding of wafers). Some distinctions in the parameters are associated with the changes of the extended defect strain fields due to specific conditions of their preparing.

Arsenic antisite defects in p-GaAs grown by metal-organic chemical-vapor deposition and the EL2 defect

Epitaxial layers of p-GaAs grown on p+-GaAs substrates by low-pressure metal organic chemical vapor deposition have been investigated using deep level transient spectroscopy (DLTS). One dominant peak and other relatively small peak, corresponding to deep levels at Ev+0.55 eV and Ev+0.96 (low field energies), respectively, have been observed in the lower half of the band gap. Investigation with double-correlation DLTS reveals that the measured thermal emission rate of holes from the dominant level is strongly dependent on the junction electric field. Detailed data on this field enhancement have been analyzed in terms of different available theoretical models. The hole capture cross section for the dominant deep level has been found to be temperature dependent. Detailed data on the temperature dependence of the hole capture cross section have been interpreted in terms of the multiphonon carrier capture mechanism, yielding a capture barrier of 0.11 eV. In order to get deeper insight into the nature and origin of these inadvertent (intrinsic) defects, thermal annealing behavior of these levels has also been studied. Analyses of field dependence and hole capture data, in combination with the annealing study, suggest that the dominant level is associated with an arsenic-antisite (AsGa) defect. Probable association of this dominant level with the doubly charged state of the well-known EL2 defect has been discussed in detail.

Doubly charged state of EL2 defect in MOCVD-grown GaAs

EL2 is the ubiquitous native defect in crystalline GaAs grown by a variety of different techniques. It has been proposed to be a doubly charged deep-level center with two states having distinct energy levels in the band gap. While the singly charged state has been the subject of many experimental studies and is, therefore, well established, the doubly charged state has only been occasionally alluded to in the literature. This paper provides evidence for a dominant inadvertent deep level in p-type GaAs most likely to be the doubly charged state of the EL2 center. Deep-level transient spectroscopy (DLTS) has been applied to characterize epitaxial layers of p-type GaAs grown on p + GaAs substrates by low-pressure metal organic chemical vapor deposition (LP-MOCVD). A pronounced peak is observed in the majority carrier (hole) emission deep-level spectra. Thermal emission rate of holes from the corresponding deep level is found to exhibit a strong electric field dependence, showing an increase of more than two orders of magnitude with an increase of the electric field by a factor of ∼2. The thermal activation energy for this level is found to vary from 0.29 to 0.61 eV as the electric field is varied from 2.8×10 5 to 1.4×10 5 V/cm. Direct pulse-filling measurements point to a temperature-dependent behavior of the hole capture cross section of this level. We identify this inadvertent deep-level defect, commonly observed in p-type GaAs grown by a variety of different methods, with the doubly charged state of the well-known As Ga antisite related defect, EL2.

Analysis of transient currents due to the electron beam irradiation to boron-doped homoepitaxial diamond films

Abstract The time variations of electron beam-induced currents through the Schottky contact on boron-doped p-type homoepitaxially grown diamond are analyzed in order to clarify the relationship between the decay in electron density and the hole emission at a boron acceptor level after removal of electron beam pulse. It is shown that the electron density varies with a time constant corresponding to the thermal emission rate of holes in the acceptor level, which means that electron beam-induced currents are dominated by the hole emission rate at the acceptor level.

Transient current measurements after applying the electron-beam pulse on boron-doped homoepitaxial diamond films

Abstract The electron-beam induced current (EBIC) and the transient current after applying an electron beam pulse are measured on the boron-doped diamond films grown homoepitaxially by microwave plasma-assisted chemical vapor deposition. The thermal emission rate of holes at the boron acceptor level of 0.31 eV above the valence band edge are obtained from the transient current measurements. The EBIC image corresponding to the surface roughness on the diamond substrate is observed in the epitaxial film. This suggests that the electrically active defects are introduced in the film during the growth.

Thermal emission rate of deep localized states in amorphous arsenic triselenide

Deep localized-state distribution in amorphous arsenic triselenide thin films has been measured with a modulated photocurrent technique. A peak in the deep localized-state distribution is found at 0.79 eV above the valence-band mobility edge. It is also found that the thermal emission rate of holes from the localized state at the peak is almost constant in the room-temperature range but exhibits thermally activated behavior below and above the room-temperature range. This anomalous temperature dependence of the thermal emission rate is interpreted on the basis of a thermally created defect.

Electric Field Enhanced Emission of Holes from the Double Donor Level of the EL2 Defect in GaAs

Strong electric-field enhancement of the thermal emission rate of holes from the doubly ionized charge state of the EL2 defect was revealed with the deep-level transient spectroscopy in p-type GaAs and analyzed in a model of phonon-assisted tunnel effect. Similar dependence observed for the electric field directions parallel to three main crystallographic axes suggests tetrahedral symmetry of the defect which is consistent with its identification as the arsenic antisite.

Hole ionization of Mn-doped GaAs: Photoluminescence versus space-charge techniques.

The thermal quenching of the Mn-related emission in GaAs is studied by measuring both the drop in intensity and the reduction in the luminescence time decay as a function of temperature. It is shown that both these quantities are governed by a temperature-activated process with an activation energy equal to the hole-emission activation energy, which is, in turn, equal to the ground-state energy of the Mn acceptor level at ${E}_{v}$+0.11 eV. However, a large reduction is found in the thermal emission rates of holes in bulk material compared to thermal measurements made with deep-level transient spectroscopy in space-charge layers. This discrepancy is discussed in terms of a recapture mechanism which strongly affects measurements in neutral material. It is also demonstrated that great care has to be taken when the detailed-balance relationship is used for the determination of thermodynamic parameters.

Dynamic quenching of photocapacitance in CdS : Cu evaporated thin films

The effect of the primary light intensity (corresponding to the fundamental absorption edge) on the infrared quenching of photocapacitance (PHCAP IR quenching) in CdS : Cu evaporated films has been studied. Two methods, viz., the two-beam and three-beam methods, for PHCAP IR quenching on detecting deep Cu levels are developed. It has been found that PHCAP IR quenching depends on the primary light intensity, that is, the rates for capturing holes into Cu deep acceptor levels [Cu+ levels and (Cu+Cu+) levels] vary as the primary light intensity changes. The experimental results are consistent with the calculations based on the three-state model of Cu quantitatively. The photoionization cross sections and thermal emission rates of holes were also measured.

Field-independence of thermal emission rate in Au-doped silicon

The thermal emission rate of holes, e t p , has been measured from dark leakage currents for the Au acceptor level in silicon diodes at different electric fields and found to be field independent for average electric fields below 10 5V/cm.