Double-correlation Deep Level Transient Spectroscopy Research Articles

Field dependence of the E1′ and M3′ electron traps in inductively coupled Ar plasma treated n-Gallium Arsenide

Inductively coupled Ar plasma etching of n-type (Si doped) Gallium Arsenide (GaAs) introduces several electron traps, Ec – 0.04 eV (labelled E1′), Ec – 0.19 eV, Ec – 0.31 eV, Ec – 0.53 eV, and Ec – 0.61 eV (behaving like the well documented M3 and labelled M3′ in this study), of which the metastable defects Ec – 0.04 eV (E1′), and Ec – 0.07 eV are novel. Furthermore, E1′ and M3′ exhibit strong field enhanced carrier emission. Double-correlation deep level transient spectroscopy was used to investigate the field dependent emission behaviour of these two defects. It is shown that for both traps, the observed enhanced emission is due to phonon assisted tunnelling. The latter observation is contrary to the literature reports suggesting that enhanced carrier emission for M3 occurs via the Poole-Frenkel mechanism.

Effects of irradiation and annealing on deep levels in rhodium-doped p-GaAs grown by metal-organic chemical-vapor deposition

This paper reports a detailed study of the effects of irradiation and thermal annealing on deep levels in Rh-doped p-type GaAs grown by low-pressure metal-organic chemical-vapor deposition, using deep level transient spectroscopy (DLTS) technique. It is found upon irradiation with alpha particles that, in addition to the radiation-induced defect peaks, all the Rh-related peaks observed in majority, as well as minority-carrier emission DLTS scans show an increase in their respective concentrations. The usually observed α-induced defects Hα1, Hα2, and Hα3 are found to have lower introduction rates in Rh-doped samples, as compared to reference samples (not doped with Rh). Alpha-irradiation has been found to decompose the two minority carrier emitting bands (one at low temperature ∼150 K and the other at ∼380 K) observed prior to irradiation into distinct peaks corresponding to deep levels Rh1 and Rh2 and EL2 and Rh3, respectively. A similar effect is also observed for the majority-carrier emitting band composed of hole emission from deep levels RhA and RhB, which separate out well upon irradiation. Further, from the double-correlation DLTS measurements, the emission rates of carriers from the radiation-enhanced peaks corresponding to deep levels Rh1, Rh2, Rh3, and RhC were found to be dependent on junction electric field. For RhC, the field dependence data have been analyzed in terms of the Poole-Frenkel model employing a 3-dimensional Coulomb potential with q = 2e (electronic charge). Temperature dependence of the hole capture cross-sections of the levels RhA and RhC was also studied quantitatively. The observed dependence of the hole capture cross-section of RhC on temperature can be interpreted in terms of multiphonon capture model, yielding a capture barrier of 0.2 eV and σ(∞) = 2.3 × 10−14 cm2. The results of irradiation and isochronal thermal annealing study, in combination with the theoretical analysis of the field dependence of hole emission data, lead us to interpret the levels RhA and RhB as charged centers and probably complexes of arsenic anti-site defect (AsGa) with Rh-impurity, (AsGa-Rh). The levels Rh1 and Rh2 are also proposed to be complexes, albeit of a different type, of arsenic anti-site defects (AsGa) and Rh-impurity (AsGa-Rh), while the level RhC is likely to be a doubly-charged complex center composed of arsenic interstitial (IAs) and Rh-impurity (IAs-Rh).

Phonon-Assisted Tunneling from Z 1/Z 2 in 4H-SiC

n-Type 4H-SiC bulk samples with a net doping concentration of 2.5 × 1017 cm−3 were irradiated at room temperature with 1-MeV electrons. The high doping concentration plus a reverse bias of up to −13 V ensures high electric field in the depletion region. The dependence of the emission rate on the electric field in the depletion region was measured using deep-level transient spectroscopy (DLTS) and double-correlation deep-level transient spectroscopy (DDLTS). The experimental data are adequately described by the phonon-assisted tunneling model proposed by Karpus and Pere.

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.

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

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.

Electric field enhancement of electron emission rates from Z1/2 centers in 4H-SiC

Z 1 / 2 defect centers were produced by irradiating 4H-SiC bulk samples with 1 MeV electrons at room temperature. The emission rate dependence on the electric field in the depletion region was measured using deep level transient spectroscopy and double-correlation deep level transient spectroscopy. It is found that the Z1/2 defect level shows a strong electric field dependence with activation energy decreasing from Ec−0.72 eV at zero field to Ec−0.47 eV at 6.91×105 V/cm. The phonon assisted tunneling model of Karpus and Perel [Sov. Phys. JETP 64, 1376 (1986)] completely describes the experimental data. This model describes the dependence of the emission rate on electric field F as en(F)=eno exp(F2/Fc2), where Fc is the characteristic field that depends on the phonon assisted tunneling time τ2. The values of Fc and τ2 were determined and the analysis of the data leads to the suggestion that Z1/2 may be a substitutional point defect.

Electric field effect on the emission rate of H4F and H4S hole traps in InP

The electric field effect on the emission rate enhancement of the H4F and H4S hole trap in highly Zn-doped InP has been examined using the deep level transient spectroscopy (DLTS) and double correlation DLTS (DDLTS). The DLTS and DDLTS results have been found to be in good agreement for low and intermediate electric fields, but they disagree for large field effect. Comparing our emission data with the theory, we have found that H4F obeys the quantum model of phonon-assisted tunneling, while H4S follows the Poole–Frenkel model employing a three-dimensional screening Coulombic potential. Our results show that the H4S defect can be attributed to a charged (Vp–Zn) complex.

4 d transition-metal impurity rhodium in GaAs grown by metal-organic chemical vapor deposition

Deep levels associated with 4d transition-metal impurity rhodium have been investigated in GaAs epitaxial layers grown by metal-organic chemical vapor deposition, using deep level transient spectroscopy (DLTS) technique. A comprehensive study of deep levels in the entire bandgap of GaAs has been carried out using both n- and p-type GaAs crystals over a wide temperature scan range, 12–470 K. In the n-type, Rh-doped material, two prominent broadbands of deep levels are found to be associated with Rh impurity; one in the upper-half and the other in the lower-half bandgap. In addition, one relatively small peak at the high temperature end of the majority-carrier emission spectra, corresponds to a deep level at Ec−0.92 eV, is also detected in the n-type Rh-doped samples. The minority carrier (hole) emission band in n-type material is found to consist of a doublet of hole emitting deep levels, labeled RhA and RhB, in the lower-half bandgap. This doublet is clearly observed to correspond to two Rh-related deep levels, labeled RhA and RhB, in the majority-carrier emission spectrum of p-type GaAs. In addition, a small hole emission peak, RhC, at the high-temperature end of the spectrum of p-type material corresponds to a deep level at Ev+0.87 eV. Data on directly measured carrier capture cross sections of deep levels are reported, wherever experimentally possible. Detailed double-correlation DLTS measurements are performed to investigate the characteristics of the observed Rh-related deep levels. The broad deep-level band in the upper-half bandgap, as well as the lower-half bandgap levels, RhA and RhB, are found to exhibit pronounced dependence of the thermal emission rates on electric field. While the former band cannot be resolved into component peaks, detailed data on the electric field dependence of hole emission rates are reported for the levels RhA and RhB over a range of measurement temperatures and analyzed in the light of the available theories. This analysis suggests the deep level RhB to be associated with a charged center while the deep level RhA is probably associated with an autolocalized self-trapping center.

Electrical characterization of alpha radiation-induced defects in p-GaAs grown by metal-organic chemical-vapor deposition

Investigations of the alpha particle irradiation-induced defects in low-pressure metal-organic chemical-vapor deposition grown p-GaAs have been carried out. By employing deep-level transient spectroscopy, at least seven radiation-induced deep-level defects have been observed in the lower half of the band gap in the temperature range of 12−475 K. Double-correlation deep-level transient spectroscopy measurements show three prominent levels: two known radiation-induced levels namely, Hα1 and Hα5, and one inadvertent center HSA, present before irradiation, to exhibit a significant dependence of thermal emission rate on the junction electric field. For Hα1 and HSA the field-enhanced emission data are well fitted with a Poole-Frenkel model, using a three-dimensional square-well potential with radius r=3.2 and 1.43 nm, respectively. The field effect for Hα5 has been explained by a square-well potential in combination with a phonon-assisted tunneling process. Detailed data on the carrier capture cross section for all three levels have been obtained. The hole capture cross section for the levels Hα1 and Hα5 are found to be temperature independent, while for HSA, the hole capture data show a dependence on temperature. The dependence of hole capture cross section of HSA on temperature has been explained in terms of multiphonon capture mechanism, yielding a capture barrier of 0.13 eV and σ(∞)=1.5×10−14 cm2. These analyses lead us to conclude that the levels Hα1 and HSA are associated with a charged center, while the level Hα5 is most likely a substitutional defect in GaAs.

Electrical Characterization of N+-implanted n-type ZnO Single Crystals: p-n Homojunction and Deep Level Defects

AbstractUnintentionally doped n-type ZnO single crystals were implanted by nitrogen ions with different fluences of 1013, 1014 and 1015 cm−2 respectively. ZnO p-n homojunction was successfully fabricated due to the formation of p-type layer after 650°C post-implantation annealing in air for 30 minutes. Further thermal evolution of deep level defects was studied through thermal annealing up to 1200°C. Electrical characterization techniques including current-voltage (I-V), capacitance-voltage (C-V), Deep Level Transient Spectroscopy (DLTS) and double-correlation DLTS (DDLTS) were used for investigating the control sample, all the as-implanted and annealed samples through Au/n-ZnO Schottky diodes as well as ZnO p-n junctions. Detailed electrical properties of fabricated devices and characteristics of implantation induced defects were analyzed based on plentiful DLTS spectra. Moreover, low-temperature photoluminescence experiments of all the as-implanted and annealed samples were performed and the correlation between results from electrical and optical characterizations was discussed.

Carrier loss channels for non-collected carrier in InAsxP1−x∕InP multiquantum well solar cells

We present here the direct observation of majority carrier (electron) defects generation from chemical-beam epitaxy grown InAsxP1−x∕InP multiquantum-well solar cell structures by deep level transient spectroscopy. Four dominant majority carrier levels E1, E2, E3, and E4 at energy position EC−0.17eV, EC−0.25eV, EC−0.57eV, and EC−0.75eV below the conduction-band edge have been observed. Detailed analysis of double-correlation deep level transient spectroscopy (DDLTS) measurements shows that traps E1, E2, E2, and E4 are located at the well-barrier interfacial zone or/and extended over the whole region occupied by the quantum wells. The midgap center E3 has large capture cross sections and is found to exhibit significant dependence of the thermal emission rates on electric field, from DDLTS measurements. These characteristics indicate that the electron trap E3 at EC−0.57eV acts as a strong recombination center and could be responsible for the main carrier loss channel for non-collected carrier in the device.

Electric-field-enhanced electron emission from the EL5 deep-level defect in GaAs

Double-correlation deep-level transient spectroscopy has been used to study the electric-field-induced thermal emission of electrons from the EL5 defect in n-type GaAs crystal. Strongly anisotropic electric-field enhancement of this emission, which was the largest for the electric field parallel to the 〈1 0 0〉 crystallographic direction and the smallest for the 〈1 1 1〉 configuration, points to the trigonal symmetry of the defect potential and a strong coupling of the defect to the lattice vibronic modes. In view of the revealed results it is argued that a close pair divacancy complex can be responsible for the EL5 defect.

Donor-like Deep Level Defects in GaN Characterized by Double-correlation Deep Level Transient Spectroscopy

AbstractSi doped GaN grown by molecular beam epitaxy on sapphire substrates were characterized by capacitance transient spectroscopy. Conventional deep level transient spectroscopy (DLTS) measurements displayed six deep level defects, labeled A1, A, B, C1, C, and D, with activation energy ranging from 0.20 to 0.82 eV below the conduction band. Based on the logarithmic dependence of the DLTS spectral peaks on the filling pulse width, it is deduced that the defects A, B, C, and D are concentrated in the vicinity of line dislocations. Double-correlation DLTS (DDLTS) measurements, on the other hand, showed that only defects A (0.82 eV) and D (0.22 eV) exhibited deep donor-like characteristics. Following a 1.0 MeV electron irradiation of the GaN sample, one radiation-induced peak, E, with activation energy less than 0.20 eV was observed in the DLTS spectrum. However, after annealing at 350 °C, this DLTS peak intensity was found to diminish significantly.

Deep levels in rhodium-doped p-type MOCVD GaAs

p-type GaAs epilayers grown by metal-organic chemical vapour deposition (MOCVD) technique, doped in situ with rhodium (Rh) impurity, have been studied by deep level transient spectroscopy (DLTS). A composite peak consisting of emission signals from at least two deep levels in the lower-half band gap is identified with Rh. This peak is resolved using double-correlation DLTS (DDLTS) measurements, providing the clear energy positions of the Rh-related deep levels as Ev+0.35eV and Ev+0.51eV. Emission rate signatures and other parameters are reported for these deep levels. They are observed to show electric-field dependent emission signatures. No significant minority carrier (electron) deep level could be clearly identified with Rh due to the presence of significant inadvertent features in the injection DLTS spectrum. Results are compared with our earlier study of Rh-doped, n-type, MOCVD GaAs.

Characteristics of deep levels associated with rhodium impurity in n-type GaAs

Deep levels have been characterized in n-type GaAs crystalline films grown by metalorganic chemical vapor deposition, doped in situ with 4d transition metal, rhodium, using the deep level transient spectroscopy (DLTS) technique. Two prominent broad bands of deep levels are found to be associated with Rh impurity, one in the upper half and the other in the lower half of the band gap. The band of electron emitting deep levels is shown to extend from 0.57–0.67 eV below the conduction band edge while the hole emitting deep levels band peaks at Ev+0.42 eV. Detailed double-correlation DLTS measurements are performed to investigate the characteristics of the observed Rh-related deep levels. Both deep level bands are found to exhibit significant dependence of the thermal emission rates on the electric field from these measurements. The observed variation of the peak profile with the capture time for the electron emission band and theoretical analysis of the field dependence data support a band-like-extended-defect nature of this deep level band.

Osmium Related Deep Levels in Indium Phosphide

Deep energy levels arising from doping of n- and p-type InP with the 5d transition metal Os are studied, using electrical and optical deep level transient spectroscopy. Electrically active Os-related deep level concentrations up to 8.2 × 1015 cm—3 are observed representing up to 20% of the chemical concentration. Three prominent levels with low-electric-field activation energies of EV +0.29, EC — 0.32 and EV +0.53 eV, labelled OsA, Os1 and OsB, respectively, are identified. Double-correlation deep level transient spectroscopy measurements show strong dependence of carrier emission rates on the electric field for all the three levels. All three levels exhibit a stronger field effect than that reported for any other deep level in InP. The field effect can be interpreted in terms of a phonon-assisted tunneling mechanism, merging in a direct tunneling process at high field strengths for both Os1 and OsA. Detailed data are obtained on the carrier capture cross-sections and their temperature dependence for all three levels. In the case of OsA the data can be interpreted in terms of a multiphonon capture model.

A donorlike deep level defect in Al0.12Ga0.88N characterized by capacitance transient spectroscopies

Si-doped, n-type heteroepitaxial layers of Al0.12Ga0.88N grown by metalorganic chemical vapor deposition on SiC substrates were characterized by capacitance transient spectroscopies. Conventional deep level transient spectroscopy (DLTS) reveals the presence of a dominant deep level with an activation energy for electron emission to the conduction band of (0.61±0.02) eV. The activation energy of this deep level displays a pronounced field dependence as determined from double-correlation DLTS (DDLTS), which is indicative of a deep donor level in n-type semiconductors. A deep level is observed by optical-DLTS (O-DLTS) with a threshold energy for electron photoemission to the conduction band of 0.77 eV, which appears to be of identical origin as the dominant deep level detected by DLTS. Two additional deep levels are detected with O-DLTS in the upper half of the band gap of our Al0.12Ga0.88N sample with threshold energies of 0.83 and 1.01 eV.

Anomalous electronic properties of a hydrogen-related deep donor in c-Si.

The effect of the electric field on the thermal emission rate of electrons from the hydrogen-carbon deep donor level in Si has been investigated by means of double-correlation deep-level transient spectroscopy. The results show for the first time an anomalous strong dependence of the activation energy of a deep level on the electric field to the extent of \ensuremath{\cong} 31 meV/${10}^{4}$ V ${\mathrm{cm}}^{\ensuremath{-}1}$. A tentative model is considered which takes into account that the electronic properties of hydrogen depend on its lattice site in the crystal, as predicted by theory. The zero-field activation energy for electrons of the H-C complex was found to be 185 meV.

Deep hole traps in p-type nitrogen-doped ZnSe grown by molecular beam epitaxy

P-type nitrogen-doped ZnSe grown on n+-GaAs by molecular beam epitaxy has been studied by deep-level transient spectroscopy (DLTS) and double correlation DLTS. To achieve p-type doping of ZnSe, we employed an active nitrogen beam produced by a free-radical plasma source. Four hole traps—with activation energies of 0.22, 0.51, 0.63, and 0.70 eV—were detected by DLTS. Two of these—those at 0.51 and 0.63 eV—have never been observed before in ZnSe. They are probably introduced to the material by nitrogen doping. The properties of the other two traps—at 0.22 and 0.70 eV—support the hypothesis that both of them are associated with native defects, in agreement with earlier reports. To our knowledge this is the first report about direct experimental investigation of deep states in p-type ZnSe.

Field effect on electron emission from the deep Ti donor level in InP.

The effect of electric field on the thermal emission of electrons from the ${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{4+}$ deep donor level in InP has been investigated. Double-correlation deep-level transient spectroscopy as well as differential-isothermal-capacitance transient measurements have been carried out on low-pressure--metalorganic-chemical-vapor-deposition-grown InP:Ti samples. It is found that the emission rates are strongly field dependent increasing by up to a factor of 17 corresponding to an increase of the field by a factor of 3.5 in the measured temperature range of 260 to 340 K. The experimental data are well fitted with a Poole-Frenkel model employing a three-dimensional square-well potential associated with the ${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{4+}$ level with a radius r=4.6 nm. The fit of this model to the experimental data yields variations in the activation energy, \ensuremath{\Delta}E=0.48\ifmmode\pm\else\textpm\fi{}0.02 eV to 0.57\ifmmode\pm\else\textpm\fi{}0.02 eV, depending upon the actual field strength. An extrapolated zero-field \ensuremath{\Delta}E(0)=${\mathit{E}}_{\mathit{C}}$-${\mathit{E}}_{\mathit{T}}$=0.59\ifmmode\pm\else\textpm\fi{}0.02 eV is found. The electron-capture cross section is determined to be \ensuremath{\approxeq}(6.6\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ ${\mathrm{cm}}^{2}$. Thus, the controversy about the previously reported variations in \ensuremath{\Delta}E values is resolved. A comparison of \ensuremath{\Delta}E(0) with the ${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{4+}$ energy position in GaAs and ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As shows that the energies are within 20 meV horizontally across the heterojunction, confirming a prediction of the ``internal-reference'' rule for the energy position of transition-metal levels in isoelectronic semiconductors.