Transient Spectroscopy Method Research Articles

Charge-based deep level transient spectroscopy of undoped and nitrogen-doped ultrananocrystalline diamond films

A comparative study of electrically active defects has been performed for undoped and nitrogen-doped nanocrystalline diamond thin films deposited on Si substrates from CH 4/Ar/H 2 and CH 4/Ar/N 2 gas mixtures using microwave and d.c. plasma CVD techniques. The method of charge-based deep level transient spectroscopy (Q-DLTS) was applied to obtain information on the concentration, activation energy and capture cross-section of native and nitrogen-induced defects. A common feature in Q-DLTS spectra of undoped films was the presence of a deep level with the activation energy of 0.13–0.22 eV. The Q-DLTS spectra of nitrogen-doped films, however, exhibited a shallow level peak with the activation energy of approximately 0.05 eV. The density of the shallow defects was found to increase with increasing concentration of incorporated nitrogen. The photoelectrical properties of the films were also studied. The kinetics of photoresponse to a high intensity light pulse (in open circuit condition at zero bias) was measured. These photoresponse data were obtained at saturation conditions and were used for designing the energy band diagram for the p-Si/UNCD film/metal and n-Si/UNCD film/metal heterostructures studied.

Intra- and Intermolecular Photochemical Properties of Poly(amidoamine) Dendrons with an Anthracene at Focal Point

Abstract Photophysical and photochemical properties of poly(amidoamine) dendrons containing an anthracene at the focal point have been studied by the steady-state and transient spectroscopic methods in solution. The fluorescence lifetime of the anthracene moiety in the higher generation dendron (G3.5) is slightly shorter than that of the lower generation homologue (G0.5). On the other hand, the triplet lifetime of G3.5 is longer than that of G0.5. The bimolecular rate constants for energy transfer from the triplet states of the anthracene moiety to O2 (kO2) and for T–T annihilation (kTT) were almost the same for the anthryl dendrons, G3.5 and G0.5, suggesting that the dendron groups do not hinder the approach of O2 or the anthracene moiety. Photodimerization of G3.5 took place at a similar rate to G0.5, while the photodissociation rates of these anthracene dimers increase in the order of anthracene > G0.5 > G3.5, suggesting the presence of some attractive forces between dendron wedges.

Post-Annealing Effects on Fixed Charge and Slow/Fast Interface States of TiN/Al2O3/p-Si Metal–Oxide–Semiconductor Capacitor

The fixed charges (Nf) and the “slow” (Nsi) and “fast” (Dit) interface states of TiN/Al2O3/p-Si metal–oxide–semiconductor (MOS) capacitors were investigated by the capacitance–voltage and deep level transient spectroscopy (DLTS) method. In addition, small pulse DLTS (SP-DLTS) analysis was performed for a more precise estimation of energies and capture cross sections of the interface states. The variations in the Nf, Nsi and Dit with various post-annealing conditions were evaluated. Annealing under a H2 atmosphere effectively reduced the Nf, Nsi, and Dit. The Dit at an energy of 0.35 eV from the valence band decreased from 1×1012 cm-2eV-1 at the as-fabricated state to 4×1011 cm-2eV-1 after annealing at 450°C. A large peak related to minority carrier capture was detected in the high temperature region of the DLTS results. The peak intensity also decreased after hydrogen annealing. This suggests that the interface states in the upper half of the Si band-gap decrease with H2 annealing.

Thin Film Electrolytes: Yttria Stabilized Zirconia and Ceria

Data obtained in an investigation of yttria-stabilized zirconia (YSZ) and ceria thin films are reviewed and discussed with special regard to the preparation conditions, namely, the temperature of deposition and the post-deposition thermal treatment of films. The structure, phase composition, electrical and dielecric properties, and problems that can be met when measuring effective and real ohmic resistances are compared with the results reported by other authors. The YSZ (CeO2)/Si interfaces are studied by means of deep level transient spectroscopy and feedback charge method capacitance–voltage measurements.

The long-term annealing of the cluster damage in high resistivity n-type silicon

The annealing of the cluster damage after fast neutron and high energy /spl pi//sup +/-pion irradiations is studied employing the deep-level transient spectroscopy (DLTS) method. The clusters consist mainly of divacancies. However, other unidentified defects contribute to the signal of the single negative charge state of the divacancy. The unidentified defects are located in the cluster region. Strain and deformation fields are assumed to change the emission parameters of the defects in the cluster region resulting in a distribution of energy states. Simulations of the DLTS signals, which take into account an exponential density distribution of energy states, were carried out. During annealing a decay of divacancies and the other unidentified defects is observed.

Close to midgap trapping level in Co60 gamma irradiated silicon detectors

The deep level transient spectroscopy method was applied on standard and oxygenated float-zone silicon detectors exposed to high doses of Co60–gamma irradiation. We have detected and characterized a close to midgap trapping level having an ionization energy of EC−(0.545±0.005) eV and electron/hole capture cross sections of σn=(1.7±0.2)×10−15 cm2/σp=(9±1)×10−14 cm2 respectively. This level has a strong impact on the detector performance being responsible for more than 90% of the change in the effective doping concentration. The defect is strongly oxygen related and a possible connection with the V2O complex is discussed.

The origin of charge transients in Al/undoped diamond/p-Si diodes

An experimental study of relaxation behaviour of Al/undoped diamond/p-Si diodes was conducted using charge deep-level transient spectroscopy (QDLTS) and feedback charge capacitance method (FCM) in the time domain. Prior to vacuum deposition of Al onto 5-μm-thick diamond films, the latter were exposed to a hydrogen discharge at 150 °C for 30 min. When measuring capacitance at delays of a few microseconds with respect to the trailing edge of the probing pulse ΔU at ambient temperatures, only the instantaneous capacitance C(0) corresponding to the thickness of the diamond film was detected. After shifting the excitation and processing of the charge transients to the region of tens of milliseconds, excess capacitance (charge) is observed, its value depending on temperature. Both isothermal and thermal-scan QDLTS measurements revealed a broad spectrum of relaxation times indicating a Debye-type dielectric relaxation, i.e. the amplitude of the QDLTS peak is a linear function of ΔU. The thermal activation energy ΔE≈0.13 eV of the spectral components corresponding to the maximum of the signal matches perfectly the activation energy of dc conductivity at equivalent temperatures. The origin of the dielectric relaxation is explained in terms of a Maxwell–Wagner polarisation due to a conducting phase embedded in the semi-insulating matrix of the diamond films, the width of the spectrum of relaxation times reflecting the spread of the sizes of microcrystallites. The results may also be useful for finding the demarcation temperature of detecting response from deep traps located within the depletion region at the Al/diamond interface.

Defect generation in crystalline silicon irradiated with high energy particles

High resistivity silicon with different concentrations of the impurities oxygen and carbon were irradiated with neutrons and charged particles. The deep level transient spectroscopy (DLTS) method is used to determine the defect parameters. During irradiation of silicon with particles lattice atoms are displaced and the primary defects silicon interstitials and vacancies form the impurity defects C i, C iC s, C iO i and VO i. In the dense displacement regions mainly divacancies VV are formed. The radiation-induced defects change the macroscopic parameters of silicon detectors. During irradiation with neutrons mainly clusters are created. During irradiation with charged particles the generation of single isolated displacements is enhanced due to Coulomb scattering. This is the main difference between irradiation damage after charged particle and neutron irradiation. The higher radiation tolerance of oxygen enriched silicon after charged particle irradiation is related to the higher introduction rates of impurity defects, because only the reaction kinetic of point defects is influenced by the impurity content. The cluster damage is less particle dependent and the threshold energy at which a recoiled silicon atom starts to create a cluster is estimated to be 300 eV.

Real defect concentration measurements of nuclear detector materials by the combination of PICTS and SCLC methods

The measurement of the real defect concentration by Photo-induced current transient spectroscopy method (PICTS) is still unattainable owing to the presence of reflecting metal layer contacts that avoid the knowledge of the real absorbed photons number and then the real photogenerated current in the sample. The combination of the two methods PICTS and space charge limited current (SCLC) allows to the extraction of the mean apparent absorption coefficient of the excitation light in the considered sample, as a consequence that leads to solve few main problems like: the scaling of PICTS spectra in term of real defect concentration and the μτ product evolution.

He ++-irradiated beryllium-doped Al 0.5Ga 0.5As MBE layers

In the present paper the deep-level transient spectroscopy (DLTS) method was applied to investigate defects in Be-doped Al 0.5Ga 0.5As created during He ++-ion bombardment. The samples were irradiated at room temperature with two fluences of 0.3 MeV He ++ ions: 10 11 cm −2 and 10 12 cm −2 . The studied samples had a net acceptor concentration equal to 10 16 cm −3 . It was found that irradiation increases the concentration of three traps and produces at least two new traps. It was possible to determine the activation energy for one of them as being equal to 0.54 eV.

The influence of target temperature and photon assistance on the radiation defect formation in low-fluence ion-implanted silicon

The formation process of secondary radiation defects in silicon crystals subjected to low-dose photon-assisted ion implantation (PAI) was investigated by the deep-level transient spectroscopy (DLTS) method. Approximately equal amounts of primary radiation defects with similar spatial profiles were introduced in n- and p-Si samples by low ( ∼10 11 cm −2 ) dose implantation of oxygen, nitrogen or argon ions under varying temperature and photoexcitation conditions. The analysis of DLTS spectra of the samples produced has revealed significant differences in the process of defect formation as well as the nature of the defects generated in n- and p-Si. The position of the predominant peak on the n-Si DLTS spectra, attributed to the divacancy complexes, is shown to be independent of the implantation conditions. This is not the case for p-Si where the positions of dominant peaks are defined by the implantation temperature. This findings indicate the qualitative difference in the defects formed in n- and p-Si. The defects measured in n-Si are mainly divacancy complexes whereas two other kinds of competing defects are formed in p-Si, each having different optimum formation temperature. Both the low implantation temperature and low power density photoexcitation of the n-Si crystals were proved to stimulate the formation of divacancies. The same experimental conditions cause the suppression rather than stimulation of total defect formation in p-Si crystals. However, at high power density, the photoexcitation activated the formation of defects in either kind of Si samples. The efficiency of photoexcitation-prompt defect formation is temperature dependent both in n- and p-Si, the dependence being direct for the former and reverse for the latter Si types. In addition, the role of photon assistance in the process of defect formation in n-Si was shown to be influenced by the mass of implanted ions. The impact of photoexcitation is prominent for light ions and tends to decrease for the heavy ones.

Carrier profiles and electron traps at a growth-interrupted layer in GaAs fabricated by a focused ion beam and molecular beam epitaxy combined system

A thin Si-doped layer was fabricated over a laterally selected area on a molecular beam epitaxy (MBE)-grown GaAs surface by 200 eV or 30 keV Si focused ion beam (FIB) implantation and successive overlayer regrowth using an FIB/MBE combined system. Characteristics of the buried doped layer were investigated by means of capacitance–voltage ( C– V) and deep level transient spectroscopy (DLTS) methods. It was found that irradiation damages can be reduced by lowering the implantation energy, and large amount of carriers were observed in the 200 eV Si implanted region without annealing. It was also found that the growth interruption induces electron traps that are located below the midgap but has fewer effects on the activation of implanted dopants.

Oxidation-induced traps near SiO2/SiGe interface

Using an Al/SiO2(wet)/Si0.9Ge0.1/n–Si/Al capacitor structure, effects of oxidation on bulk trap and interface states near the SiO2/SiGe interface are investigated. Two peaks at the energy levels of 0.23 eV (D1) and 0.40 eV (D2) below the conduction band edge are observed with the capacitance deep level transient spectroscopy (DLTS) method. The DLTS measurement results show a characteristic feature of interface states for the D1 peak. The interface state distribution obtained by the capacitance–voltage method also has a high density (6.9×1012/cm2 eV) peak at an energy level of 0.23 eV below the conduction band edge. The Si–O– dangling bonds are thought to be the source of the D1 peak. The annealing behaviors of the D2 peak show that D2 is a divacancy related bulk trap. The capture cross section and the trap density for the bulk trap D2 are 2.06×10−15/cm2 and 1.8×1014/cm3, respectively. The density of D2 is significantly reduced after low temperature postmetallization annealing.

Deep hole traps in Be-doped Al0.5Ga0.5As layers grown by molecular beam epitaxy

Deep hole traps in p-type Al0.5Ga0.5As grown by molecular beam epitaxy have been studied by the deep-level transient-spectroscopy method applied to samples with a Schottky diode configuration. Five hole traps, labeled as H0 to H4, were found. For traps H1, H3, and H4 the activation energies for emission were ET1=0.14 eV, ET3=0.40 eV, and ET4=0.46 eV, respectively. Hole emission from trap H2 was dependent on the external electric field. The emission rate obeyed the Poole–Frenkel relation. When extrapolated to zero electric field, the thermal activation energy for hole emission was ET2,0=0.37 eV. Capture cross sections for traps H1 and H4 were thermally activated with energy barriers EB1=0.04 eV and EB4=0.18 eV, respectively.

Long-time constant-capacitance DLTS investigations of 6H SiC/MOS structures: comparison of dry and wet oxidation

A long-time constant-capacitance deep level transient spectroscopy (LT-CC-DLTS) method has been established to investigate the energy distribution D it and the capture-cross-section σ n/p of states at the interface of 6H SiC/MOS structures. A comparison of dry and wet oxidation (1120°C) reveals a change in the distribution of interface states and a different magnitude of capture-cross-sections indicating that the interface states consist of at least two types of defects.

Luminescence and electrophysical characteristics of ZnSe implanted with acceptor impurities

The investigation of traps and recombination centres in structures based on ZnSe single crystals by means of the deep level transient spectroscopy, photoluminescence and electroluminescence methods are presented. The implantation of Ag +, Au + and N + ions was used for the creation of these centres. The activation energies equal to 0.26, 0.35 and 0.86 eV were determined from the temperature dependencies of the carriers emission rate from DLTS spectra for majority carriers (electrons). The levels 0.42 and 0.26 eV were observed only in the samples implanted with Ag and Au, respectively. In the case of minority carriers (holes), in all the diodes produced by Ag + ions implantation, the depth of the trap was 0.30 eV. Traps with a depth of about 0.72 eV were observed independently on various kind of impurities. In all the cases when these impurities are used together with nitrogen a hole trap with a depth of 0.47 eV is observed. The concentrations and capture cross-sections of the centres were calculated photo- and electroluminescence spectra of the implanted samples and structures are presented.

Defect studies in Cd 0.95Mn 0.05Te : Ga by DLTS

In this paper we present the results of our investigations of deep levels in bulk Ga-doped Cd 0.95Mn 0.05Te mixed crystal by deep level transient spectroscopy (DLTS) method. Four electron traps have been found with activation energies obtained from Arrhenius plots equal to 0.26, 0.53, 0.55 and 0.83 eV. For the first and the second of the traps electron capture processes have been found to be thermally activated with energetic capture barriers equal 0.15 and 0.23 eV, respectively.

Effects of Impurity between Epitaxial Layer and Substrate on Current Transient for GaAs Metal-Semiconductor Field-Effect Transistors

The effects of the impurity between the epitaxial layer and substrate (epi/sub) on the current transient were examined by the drain bias pulsed current deep level transient spectroscopy (DLTS) method. Test devices used for evaluation were GaAs metal-semiconductor field-effect transistors (MESFETs) grown by metalorganic chemical vapor deposition (MOCVD). Energy-band diagram simulation of the MESFET structure showed that the drain bias pulsed current DLTS method is suitable for determining the buffer layer quality. Negative DLTS spectra, which were regarded to be caused by the electron emission in the AlGaAs buffer layer, were observed for both the intentionally doped epi/sub sample and purified epi/sub sample. The intensity difference of these DLTS signals could be explained by the quality change of the AlGaAs buffer layers. This electron trap was determined to be the oxygen-related deep level. For the purified epi/sub sample, another positive peak was found. The origin of this “hole trap”-like peak was discussed.

ICTS Measurements of Single Grain Boundaries in ZnO:rare-earth Varistor

Properties of single grain boundaries in ZnO:rare-earth varistors were examined by the isothermal capacitance transient spectroscopy (ICTS) method. Micro-electrodes prepared by photolithography were used for measuring the behavior of single junctions in ZnO varistors. From current-voltage measurements, it was found that the non-linear exponents of single junctions varied from 3 to 14. Interface state levels existed at 0.9 eV below the conduction band edge for every junction. On the other hand, the interface state density varied from junction to junction and the non-linearity was shown to increase with increasing interface state density.

Radiation damage in InGaAs photodiodes by 1 MeV fast neutrons

Abstract Irradiation damage in In 0.53 Ga 0.47 As p-i-n photodiodes by 1 MeV fast neutrons has been studied as a function of fluence for the first time, and the results are discussed in this paper. The degradation of the electrical and optical performance of diodes increases with increasing fluence. The induced lattice defects in the In 0.53 Ga 0.47 As epitaxial layers and the InP substrate are studied by Deep Level Transient Spectroscopy (DLTS) methods. In the In 0.53 Ga 0.47 As epitaxial layers, hole and electron capture levels are induced by irradiation. The influence of the type of radiation source on the device degradation is then discussed by comparison to 1 MeV electrons with respect to the numbers of knock-on atoms and the nonionizing energy loss (NIEL). The radiation source dependence of performance degradation is attributed to the difference of mass between the two irradiating particles and the probability of nuclear collision for the formation of lattice defects.