Deep Level Transient Spectroscopy Peak Research Articles

Deep level transient spectroscopy study of electron-irradiated CuInSe2 thin films

Irradiation of high-energy (2-MeV and 3-MeV) electrons on single-crystalline n-CuInSe2 films has been investigated. From Hall-effect measurements of the film, the carrier density and mobility were decreased by increasing the electron fluence above 1×1017 cm−2. In both as-grown and electron-irradiated CuInSe2 films, the deep level transient spectroscopy (DLTS) peak, indicating electron trap, was found at around 180 K. However, Arrhenius plots of the observed DLTS peaks in as-grown and electron-irradiated films showed different behavior, suggesting the presence of electron traps introduced by high-energy electron irradiation.

Electrical characterization of impurity-free disordering-induced defects in n-GaAs using native oxide layers

Defects created in rapid thermally annealed n-GaAs epilayers capped with native oxide layers have been investigated using deep-level transient spectroscopy (DLTS). The native oxide layers were formed at room temperature using pulsed anodic oxidation. A hole trap H0, due to either interface states or injection of interstitials, is observed around the detection limit of DLTS in oxidized samples. Rapid thermal annealing introduces three additional minority-carrier traps H1 (EV+0.44 eV), H2 (EV+0.73 eV), and H3 (EV+0.76 eV). These hole traps are introduced in conjunction with electron traps S1 (EC-0.23 eV) and S2 (EC-0.45 eV), which are observed in the same epilayers following disordering using SiO2 capping layers. We also provide evidence that a hole trap whose DLTS peak overlaps with that of EL2 is present in the disordered n-GaAs layers. The mechanisms through which these hole traps are created are discussed. Capacitance–voltage measurements reveal that impurity-free disordering using native oxides of GaAs produced higher free-carrier compensation compared to SiO2 capping layers.

Study of the deep level related to a platinum–dihydrogen complex in Si by capacitance transient spectroscopy under uniaxial stress

We have applied a novel technique to combine isothermal deep-level transient spectroscopy (DLTS) with the application of uniaxial compressive stress to studying the structure of a platinum- and hydrogen-related defect, which has a gap state at 0.14 eV below the conduction band in Si. The application of 〈100〉 and 〈111〉 stresses split the DLTS peak of the defect into two components with intensity ratios of 2.3:1 and 1.1:1, respectively, which were ratios of short- to long-time components. Under 〈110〉 stress, the peak split into three components with an intensity ratio of 0.8:3.7:1. Comparing this splitting pattern to the piezospectroscopic theory of Kaplyanskii, we have uniquely determined that the defect has the orthorhombic symmetry with the C 2v point group, and have identified the defect as the Pt–H 2 complex previously identified by Uftring et al. [Phys. Rev. B 51 (1995) 9612]. We also observed that the defect was reoriented above 80 K along the applied uniaxial stress. Such reorientation occurred only when the defect level was not occupied by an electron. Our observation strongly suggests that the local motion of hydrogen around the Pt atom is remarkably affected by the charge state of the defect.

RF hydrogen-plasma-induced defects in p-Si/SiO 2 structures with submicron thermally grown oxides

Capacitance–voltage measurements at 77 and 300 K have shown that RF hydrogen plasma treatment of p-Si/SiO 2 structures with submicron oxide generates defects in the SiO 2 layer and at the Si/SiO 2 interface. The density of these plasma-induced defects is highest in the structures treated at 20°C, intermediate at 100°C and lowest at 300°C. A broad deep-level transient spectroscopy peak related to deep levels with a concentration in the order of 10 16 cm −3 was detected. The conduction of these p-Si/SiO 2 structures in the accumulation regime does not depend on the temperature in the range of 77–300 K.

Hole and Interface Traps in Mg-doped Al0.1Ga0.9N/GaN Grown by Metalorganic Chemical Vapor Deposition

Deep level traps in Mg-doped Al0.1Ga0.9N/undoped GaN heterostructures grown by metalorganic vapor deposition with different Cp2Mg molar flow rates are studied by deep level transient spectroscopy (DLTS). Two distinct hole traps were observed, one with an activation energy of 0.18 eV (AD1) and the other with an activation energy of 0.88 eV (AD2) above the valence band maximum. From an analysis of the voltage dependence of DLTS spectra, the AD1 trap is associated with a defect in the Al0.1Ga0.9N/GaN interface based on the Poole–Frenkel model to interpret the enhancement of the thermal emission rate due to potential barrier lowering. The DLTS peak intensity of the AD2 trap steadily decreases with decreasing the Cp2Mg molar flow rate. It appears that the AD2 hole trap is strongly related to Mg-related deep levels, which contribute to the strong blue emission observed by photoluminescence measurements.

Effect of surface passivation of AlGaN∕GaN heterostructure field-effect transistor

The effect of SiN passivation of the surface of AlGaN/GaN transistors is reported. Current deep level transient spectroscopy (DLTS) measurements were performed on the device before and after the passivation by a SiN film. The DLTS spectra from these measurements showed the existence of the same electron trap on the surface of the device. The DLTS spectrum obtained from the measurement of the passivated device showed a significantly lower peak for this trap. The discrepancy in the DLTS peak amplitude is explained by the effect of the passivation on the surface traps and underlines the surface nature of the major defect noticed in the device.

Electrical and optical properties of erbium-related centers in 6H silicon carbide

Implants of Er, Al and N with energies ranging from 120 keV to 2 MeV were carried out in n- and p-type 6H-SiC. The aim is to identify electrically active defects in the bandgap which can be associated with the 1.54 μm Er 3+ luminescence in 6H-SiC. Measurements are conducted by means of deep level transient spectroscopy (DLTS) as well as low temperature photoluminescence (LTPL). In n-type 6H-SiC implanted with Er, we find well known DLTS damage levels whereas strong characteristic lines of Er 3+, near 1.54 μm, are seen in the photoluminescence. In p-type 6H-SiC implanted with Er two DLTS peaks can be uniquely associated with the Er 3+, on the other hand, no luminescence is observed. Conversion of such p-type 6H-SiC into n-type, by nitrogen implantation, recovers the photoluminescence. We conclude that the Er-associated defect levels in the lower half of the gap are likely not involved in the energy transfer mechanism which is responsible for the 1.54 μm luminescence.

Stress-induced splitting of the electronic level related to a platinum–hydrogen complex in silicon

We have applied deep-level transient spectroscopy (DLTS) under uniaxial compressive stress to study the structure of a platinum- and hydrogen-related defect, which has a gap state at 0.14 eV below the conduction band minima in Si. The application of 〈1 0 0〉 and 〈1 1 1〉 stresses split the DLTS peak of the defect into two components with intensity ratios of 2.7 : 1 and 1.4 : 1, respectively, which were the ratios of the low-temperature peak to the high-temperature peak. Under 〈1 1 0〉 stress, this peak split into three components as an intensity ratio of two lower-temperature peaks to the high-temperature peak was 1.4 : 5 : 1. In addition, we observed the stress-induced alignment of the defect to the configuration corresponding to the low-temperature DLTS peak during the DLTS scan in the temperature range of 65–100 K, for all stress directions. Our results provide the first evidence to connect the electronic level at E c−0.14 eV to the atomic configuration of the Pt–H 2 complex with the C 2v symmetry previously identified by EPR.

Piezospectroscopic analysis of the hydrogen–carbon complexes in silicon

We have observed the donor ( E c−0.22 eV) and acceptor ( E c−0.16 eV) levels related to hydrogen–carbon complexes in silicon. The donor level is only detected at low temperatures after proton implantation. This hydrogen–carbon complex irreversibly reconfigures at temperatures above 225 K to a configuration characterized by the acceptor level, which is stable up to room temperature. The same acceptor level is also observed after atomic hydrogen diffusion. We have used Laplace transform deep level transient spectroscopy (DLTS) to show the influence of uniaxial stress on the electron emission process and the effect of the stress-induced alignment for the acceptor state. The pattern of the Laplace DLTS peak splittings indicate a trigonal symmetry of the defect. First principles calculations were carried out on the hydrogen–carbon defects with a view of determining their electrical levels and stress response for comparison with the experimental results.

On-line DLTS investigations of the mono- and di-vacancy in p-type silicon after low temperature electron irradiation

Using deep level transient spectroscopy (DLTS) and Laplace-DLTS, we have investigated vacancy-related defects created in boron-doped epitaxial Si by 2 MeV electron irradiations at low temperatures (⩽ 40 K) . The vacancy level is found at E v +0.12 eV together with a DLTS peak at E v +0.20 eV which anneals at ∼140 K and is tentatively identified as a vacancy in a different configuration. The emission rate of the dominant vacancy-related deep level in the temperature range from 200 to 550 K, namely the (0/+) transition of the di-vacancy (V 2), displays a very large dependence of the emission rate on the electric field strength in the depletion region of the diodes. This dependence is unexpected in terms of the classical Poole–Frenkel effect, given the neutral charge state of V 2 before hole capture. The effect of high fields appears to be caused by phonon assisted tunneling. When V anneals around 200 K, a new complex assigned to a vacancy–boron pair gives rise to two charge states. Quenching experiments with reverse bias show that the complex is bistable. It anneals at 260 K.

Deep Level Study in Heteroepitaxial 3C-SiC Grown on Si by Hexamethyldisilane

Deep levels in 3C-SiC on Si grown by chemical vapor deposition using hexamethyldisilane (HMDS) were investigated by the deep level transient spectroscopy (DLTS). 3C-SiC epilayers with various thicknesses were grown by changing the growth time. Relatively thin epilayers (<1 µm) showed DLTS signals in a wide temperature range. This indicates that these epilayers have defects distributed in a wide energy range. These defects seem to originate from the 3C-SiC/Si heterointerface. On the other hand, relatively thick epilayers (>2.2 µm) showed only one DLTS peak, which corresponds to a defect having an activation energy of about 0.25 eV. This defect is a donor defect and is identical with a defect observed in 3C-SiC grown from SiH4 + C3H8.

Characterization of near-surface traps in semiconductors: GaN

We present a simple a criterion, based on deep-level transient spectroscopy peak heights S(Vr) at two or more values of reverse bias Vr, to unequivocally determine whether or not a particular semiconductor trap is of bulk or near-surface nature. Moreover, we present an expression for S(Vr) with fitting parameters φB, the Schottky barrier height; δ, the trap penetration depth; and NT, the trap density. Application of the method to a thick, high-quality, epitaxial GaN layer, reveals two common traps which penetrate only 2700±300 Å into the layer.

Electron traps and growth rate of buffer layers in unintentionally doped GaN

The deep level spectra in a series of undoped GaN films with different GaN buffer growth rates were studied by deep level transient spectroscopy (DLTS), transmission electron microscopy (TEM) and high-resolution X-ray diffraction (HRXRD) in order to investigate correlation between dislocations and deep level defects. Two distinct deep levels were observed, one with an activation energy E1=0.19–0.23 eV and the other with an activation energy E2=0.50–0.60 eV below the conduction band. The broadening of the (1 0 2) Bragg peak with decreasing buffer growth rates was related to increasing edge dislocations and also the DLTS peak intensity of the deep level E1. The logarithmic dependence of the DLTS peak intensity on the filling pulse time indicated that the deep level E1 is associated with dislocation core sites.

Effects of uniaxial stress on the electronic state of the hydrogen–carbon complex in silicon

We applied deep-level transient spectroscopy (DLTS) under uniaxial stress to study the structure and bonding character of a hydrogen–carbon complex. The application of 〈1 1 1〉 and 〈1 1 0〉 compressive stresses split the DLTS peak into two as intensity ratios of 1 : 3 and 2 : 2, respectively, which were the ratios of the low-temperature peak to the high-temperature peak. No splitting was observed under the 〈1 0 0〉 stress. These results indicate the trigonal symmetry of the complex and the antibonding character of its electronic state, and are consistent with the previously proposed atomic model of the complex, in which the hydrogen atom occupies the bond-centered site between silicon and carbon atoms. Furthermore, under the 〈1 1 1〉 stress, we observed that the energy of the electronic state corresponding to the low-temperature DLTS peak increased linearly with stress by 23±5 meV/GPa while that of the high-temperature peak only slightly decreased with stress by 6±5 meV/GPa. Under the 〈1 1 0〉 stress, the energy of the electronic state of the low-temperature peak had almost no stress dependency and that of the high-temperature peak decreased linearly with stress by 15±5 meV/GPa. Based on the above atomic model, we can consistently understand the opposite stress dependencies under 〈1 1 1〉 and 〈1 1 0〉 compressive stresses, considering the atomic displacement of the H–C complex under the stress.

Band alignment in ZnCdTe/ZnTe and ZnCdSe/ZnSe SQWstructures grown on GaAs(100) by MBE

Molecular-beam-epitaxy-grown ZnTe/CdZnTe/ZnTe andZnSe/ZnCdSe/ZnSe strained single-quantum-well structures withnon-doping layers were investigated by cathodoluminescence (CL)and deep-level transient spectroscopy (DLTS). The activationenergies for deep levels in ZnTe and ZnSe buffer layers grownon GaAs were determined by the DLTS spectra. Moreover, anadditional DLTS peak that depends on the quantum well (QW) parametersand correlates with the QW emission line position in the CLspectra was observed. This peak is interpreted as an emissionof electrons from a ground level in the QW. Obtained DLTS andCL results were used for the estimation of the conduction bandoffset parameter QC.

Radiotracer identification of a Ta-related deep level in 4H–SiC

To identify tantalum-related deep levels, deep level transient spectroscopy (DLTS) measurements were performed on Ta-implanted n-type 4H–silicon carbide. The DLTS spectra of samples implanted with stable Ta181 exhibit one dominating peak representing a trap energy of about ET=EC−0.67 eV. Due to superimposed signals of intrinsic defects, the exact value depends on the annealing conditions. To achieve a definite assignment of this peak to tantalum, the radioactive isotope Ta177 was recoil implanted into n-type 4H–SiC. DLTS spectra measured subsequently during the nuclear decay of Ta177 to Hf177 reveal a trap with decreasing concentration according to the elemental transmutation. This effect definitely proofs the identification of a Ta-related level at 0.68 eV below the conduction band edge. There is no further DLTS peak of time-dependent height, indicating that there is no deep level of Hf in the part of the band gap investigated.

High-resolution DLTS studies of vacancy-related defects in irradiated and in ion-implanted n-type silicon

Using high-resolution Laplace deep-level transient spectroscopy (DLTS), we have compared the electron emission characteristics of vacancy-related defects in silicon. The samples include material irradiated with high-energy protons, material implanted with a heavy ion and silicon irradiated with 2 MeV electrons. We show that in the proton- and electron-irradiated material the DLTS peak in the region of the (- -/-) state of the divacancy at E c=0.23 eV contains only one feature. The DLTS peak at 250 K which contains the signal derived from the (-/0) state of the divacancy is much larger in ion-implanted silicon than in electron-irradiated silicon. The Laplace DLTS is able to resolve clearly the (-/0) divacancy state and the V–P defect, whereas conventional DLTS shows only a broad peak in that region.

Recombination center in C 60/p-Si heterojunction and solar cells

Deep level transient spectroscopy (DLTS) has been used to detect the contribution of interface-related states, responsible for minority carrier lifetime reduction in C 60/p-Si solar cells. The very low efficiency of C 60 based solar cells is found to be due to the presence of one hole level E V +0.70 eV at the interface of C 60/p-Si heterojunction. The hole capture cross-section and the variation with temperature have been determined, to account for minority carrier lifetime of the material. A large barrier for hole capture, implying a large electron–phonon interaction, characterizes the observed hole level. A pronounced reduction in DLTS peak of the dominant level ( 0.70 eV ) due to injection of electrons provides evidence of electron–hole recombination. A detailed characterization indicates that a dominant deep level, with comparable electron and hole emission rates, acts as a recombination center, which governs the minority-carrier lifetime

Deep-level transient spectroscopy and cathodoluminescence of Cd xZn 1− xTe/ZnTe QW structures grown on GaAs(1 0 0) by MBE

MBE-grown ZnTe/CdZnTe/ZnTe strained single quantum well (SQW) and multiple quantum well (MQW) structures with non-doping layers were investigated by cathodoluminescence (CL) and deep-level transient spectroscopy (DLTS). The DLTS method with electrical current relaxation was used because the as-grown structures were compensated. The activation energies of 0.21 and 0.58 eV for deep levels in ZnTe buffer layers grown on GaAs were determined by the DLTS spectra. Besides, an additional DLTS peak ( E t =34 –133 meV) that depends on the quantum well parameters and correlates with the QW emission line position in the CL spectra was observed. This peak is interpreted as an emission of electrons from a ground level of dimensional quantization in a conduction band. Obtained DLTS and CL results were used for an estimation of a conduction-band offset parameter Q C .

Motion of hydrogen in silicon revealed by deep-level transient spectroscopy under uniaxial stress

We propose a method to visualize the local motion of hydrogen in Si by combining deep-level transient spectroscopy (DLTS) under uniaxial stress with the technique of stress-induced alignment and subsequent relaxation of hydrogen-related complex defects. The model defect used is a hydrogen–carbon (H–C) complex, which has a donor level at E c−0.15 eV in Si and can be detected by DLTS as an electron trap. The splitting behavior of the DLTS peak under compressive stresses to lift the orientational degeneracy is consistent with the atomic model in which the hydrogen atom occupies the bond-centered site between silicon and carbon atoms. We have observed the stress-induced alignment of the complex under a 〈1 1 0〉 stress of 1 GPa at 250–300 K and the subsequent relaxation of stress-induced alignment after removing the stress. This behavior can be understood as the motion of hydrogen under the stress from a high-energy bond to a low-energy bond with respect to the stress direction and the subsequent relaxing motion of hydrogen via bond-to-bond jumps under no stress. By controlling the charge state of the complex with and without applying reverse bias to the Schottky junction, we have found that the hydrogen motion is greatly influenced by the charge state of the complex and hydrogen moves more easily in the neutral charge state.