Characterization Of Deep Levels Research Articles

Characterization of interface deep levels in As vapor grown EPI-GaAs

In this work vapor phase epitaxial GaAs structures are investigated by the method of transient acoustoelectric spectroscopy. At the interface between a substrate and epilayer we identified four types of defects (EL3, EL5, EL6, EL17). We have measured the cross section for electron capturing, relaxation times of trapped charge and energetic levels in forbidden zone for said defects.

Electrical characterization of deep levels existing in Mg-Si- and Mg-P-Si-implanted n InP junctions

The deep levels existing in fully ion implanted and rapidly thermally annealed InP junctions were investigated in this work. The samples were co-implanted with magnesium and silicon. An additional phosphorus implantation was carried out in some samples to study its effect. In order to characterize the traps, deep level transient spectroscopy (DLTS) and the capacitance-voltage transient technique (CVTT) were used. For a (control) sample implanted with Mg only, four deep electron levels located at the upper half of the band gap (at 0.45, 0.2 eV 0.25 and 0.27 eV below the conduction band) were detected by DLTS. On the contrary, for the Mg-Si- and Mg-P-Si-implanted samples only two of them (at 0.25 and 0.27 eV below the conduction band) were observed. Several characteristics of each trap were derived by CVTT measurements. Tentative assignments have been proposed for the physical nature of these deep levels.

Deep Level Characterization of Interface-Engineered ZnSe Layers Grown by Molecular Beam Epitaxy on GaAs

AbstractDeep level defects have been detected and analyzed in epitaxial ZnSe layers grown by molecular beam epitaxy (MBE) on GaAs and on In0.04Ga0.96As using deep level optical spectroscopy (DLOS). A series of samples, which differ only in the initial Zn:Se beam pressure ratio (BPR = 1:1, 1:10, 10:1) during the growth nucleation step, were characterized by DLOS in order to assess the dependence of bulk deep level formation on interface nucleation conditions. The transient and steady state photocapacitance measurements were performed using 100 W Quartz Halogen and 450 W Xe lamps as light sources, in the spectral range of 0.9 to 2.9 eV with a resolution better than 0.02 eV. The capacitance transients were recorded for time windows of 10 msec to 5 sec after light excitation of the sample, which was kept at a temperature of 100 K. Using semi-transparent Au Schottky contacts, several deep levels in the ZnSe layer were detected for all BPR's, with optical threshold energies of 1.1, 1.46 and 1.9 eV below the conduction band. These energies were obtained from the slope of the capacitance transient at different time intervals and were confirmed by steady state photocapacitance. The concentration of the levels was in the range 1012 to 1014 cm−3. Both the 1.1 and 1.46 eV trap concentrations were found to depend strongly on lattice mismatch conditions, whereas the latter was shown to largely depend on BPR. The optical threshold of the 1.9 eV trap correlates well with a ˜1.9 eV cathodoluminescence (CL) peak, which has been previously associated with either Zn vacancies or Gazn substitutional defects in Zn-deficient material.

Deep level capture barrier in molecular beam epitaxial grown AlAsySb1−y measured by isothermal capacitance transient spectroscopy

Improved isothermal capacitance transient spectroscopy (ICTS), which measures the entire capacitance transient as a function of time and temperature in a single temperature scan, has been implemented in a deep level trap analysis extending the characterization to include capture barrier measurement. This method eliminates inaccuracies introduced by narrow pulse widths that are difficult to reproduce accurately, providing capture barrier information more accurately and easily in addition to the usual deep level characteristics. A method of establishing ICTS experimental conditions and a method of analyzing the resulting data are described and applied to the investigation of deep levels in Te-doped AlAs0.07Sb0.93. The sample shows a single DX center trap having a deep level energy of 278 meV, a high temperature capture cross section of 1.3×10−12 cm2, and a capture barrier energy of 137 meV, clearly demonstrating the superior method of measuring a capture barrier.

Deep-level characterization in semi-insulating GaAs by photo-induced current and Hall effect transient spectroscopy

Deep levels in semi-insulating (SI) GaAs single crystals were studied by photo-induced current transient spectroscopy (PICTS) and photo-induced Hall effect transient spectroscopy (PHETS). A method of measuring the defect level density using PHETS was developed and used to measure the EL6 density in SI-GaAs. Investigations were made into EL2 and EL6, the main defect levels in SI-GaAs, to find the density distribution in the as-grown wafer and the annealing behaviour in the temperature range from 600 to 1100°C. The density distribution of EL2 across the wafer showed a so-called W-shaped pattern similar to the dislocation density, but the EL6 distribution showed an M-shaped pattern. Annealing at temperatures from 800 to 1000°C increased the density of each level, whereas annealing at 1100°C diminished it. These experimental results were well explained by tentative defect models for EL2 (AsGa VGa) and EL6 (AsGa Asi).

Deep-level characterization of p-n junction devices using trigonometric weight functions

This paper describes a method to treat capacitance transients in semiconductor junctions using trigonometric weight functions. The method is a variation of the classical deep-level transient spectroscopy (DLTS) technique using a double lock-in. The technique is suitable for measurements where the integrator module or lock-in amplifier works with a combination of sinusoidal functions multiplying the input signal before integration. The sensitivity and resolution of the method are determined and compared with the main variations of the DLTS technique. Experimental data for DX centers in p/sup +//n AlGaAs junctions are discussed. For a sample having single defects, as DX centers, the proposed method enables the defect characterization using only one spectrum.

Properties of DX center in Te-doped In1−xG axAsyP1−y/GaAs0.61 P/d0.39

We report that the Te donor forms a deep level and acts as a DX center in In1−xGaxAsyP1−y/GaAs0.61P0.39. The characteristics of Te-related deep level is investigated by deep-level transient spectroscopy and thermally stimulated capacitance measurements. The deep level has a thermal activation energy of 0.14±0.01 eV regardless of the alloy composition of In1−xGaxAsyP1−y. Persistent photoconductivity is observed at low temperature in all Te-doped In1−xGaxAsyP1−y/GaAs0.61P0.39 samples. The compositional dependence of deep trap density is explained by the energy difference between the conduction band minimum and the DX level.

Additive double gate analysis in photoinduced current transient spectroscopy: Application to cuprous oxide

AbstractPhotoinduced current transient spectroscopy, in its conventional doublegate version, has been used extensively in the characterization of deep levels in semiinsulating materials. The analysis of the digitally captured transient signals by the post capture double gate method is a parallel technique with much more advantages. One of the drawbacks of the latter is, of course, the excessive time needed to capture data with a high signal‐to‐noise ratio. We have shown that the capturing time can be chosen tobe relatively low and the signal‐to‐noise ratio can be improved by a post capture data analysis referred to as the additive double gate analysis. The usefulness of this approach is demonstrated by the results obtained, for the first time, on high resistivity films of cuprous oxide. Thetechnique leads to the identification and measurement of the parameters of a few deep levels. The apparent activation energies of these levels are 0.33, 0.47, 0.49, and 0.59 eV. The corresponding capture cross sections are 2 × 10−17, 7 × 10−12, 1 × 10−15 (7 × 10−13), and 4 × 10−15 cm2, respectively.

Determination of capture barriers of defects for GaAs alloys and transient photo-resistivity spectroscopy

Si-doped Ga0.7Al0.3As grown by molecular beam epitaxy (MBE) and undoped Ga0.47Al0.53As grown by chemical beam epitaxy (CBE) have been investigated using a new deep level characterization method-transient photo-resistivity spectroscopy, which we recently developed. This method measures directly the capture process of deep centers. In GaAlAs, apparent capture barrier energy EB = 0.25 eV of DX center was determined and intrinsic capture barrier energy Eσ = 0.16 eV was directly measured. In GaInAs, a defect with capture barrier energy EB = 0.28 eV was observed. The result proved that DX centers capture electron only from band L, belonging to small lattice relaxation model. The theoretical deduction of transient photo-resistivity spectroscopy was improved.

Characterization of deep levels and carrier compensation created by proton irradiation in undoped GaAs

Deep levels and carrier compensation created in undoped metal-organic chemical-vapor deposition grown GaAs by low fluence proton irradiation (1×108−1×1010 cm−2) are investigated by the deep level transient spectroscopy technique and capacitance-voltage profiling. At least five main electron traps are observed after room-temperature irradiation in addition to the EL2 present in the as-grown material. Irradiation generates additional EL2, which annihilate at much lower temperatures than one would expect for isolated EL2. However, with further increase in irradiation fluence, the magnitude for this additional increment begin to decrease. The apparent decrease in the EL2 peak is accompanied by an increase of a broad peak in the deep level transient spectroscopic spectrum. This broad peak has a highly nonexponential capacitance transient and it is suggested to result from the interaction of the additional EL2 with EL6. One of the observed traps, with energy level, (Ec−0.40) eV, has not previously been reported in proton irradiated GaAs. The signature of this trap resembles that of EL5 and is quite stable at moderate annealing temperatures; annihilating completely only at a temperature of ∼600 °C. This level shows a saturation effect with increasing irradiation dose and we believe it is related to complex defect-impurity formation. The temperature dependence of the carrier profiles reveals some complex behavior of carrier compensation, including acceptor- and donor-like properties of the various traps.

Characterization of Deep Levels in Si-Doped InxAl1-xAs Layers Grown by Molecular Beam Epitaxy

Deep levels in Si-doped Inx Al1-x As layers grown by molecular beam epitaxy were systematically investigated, changing the alloy composition for the first time. Deep level traps were characterized by deep level transient spectroscopy (DLTS) measurements and photoluminescence (PL) measurements. Two kinds of deep electron traps, E1 and E2 were observed. Least squares fitting curves of all data on the E1 and E2 traps were almost parallel to the Γ-band edge. From the observed dependence of trap level position on the alloy composition as well as from the comparison between DLTS and PL results, observed traps seem to be not DX center like donors but normal deep donors associated with the Γ-band.

Characterization and identification of the deep levels in V doped CdTe and their relationship with the photorefractive properties

Deep level characterization by photoinduced current transient spectroscopy, deep level transient spectroscopy and deep level optical spectroscopy is presented on vanadium doped CdTe crystals grown for photorefractive applications. A main electron trap at 0.95 eV, connected with V doping, is proposed to be the main deep level involved in the photorefractive effect of CdTe:V on the bases of the σ n 0 and σ p 0 ionization cross-sections measurements as compared to spectroscopic results of the electron-hole competition factor obtained on CdTe:V.

Deep-level characterization of [formula omitted] layers grown by low pressure metal-organic chemical vapor deposition

In this study, non-intentionally doped Al x In 1−x As layers lattice matched to InP grown by low pressure metal/organic chemical vapor deposition have been characterized. We show the presence of a deep level located at E c −0.62 eV associated with impurity contamination. This contamination appears near the sample surface. We observe the passivation of deep levels and of the Si shallow donor level in this surface zone which leads to conclusion that a hydrogenation effect occurs.

Characterization of the damage induced in boron-implanted and RTA annealed silicon by the capacitance-voltage transient technique

The electrically active profiles and the induced defects in boron-implanted silicon under different implantation conditions were measured. The implantation profiles were derived from conventional capacitance-voltage measurements. Deep-level defects induced by the technological process have been characterized. Deep-level transient spectroscopy (DLTS) seems not to be sufficient to study the variations of the deep-level properties along the space-charge region of the junctions. In order to achieve a more complete deep-level characterization we have set up a new technique, named the capacitance-voltage transient technique (CVTT), which allows us to determine the spatial variation of the concentration and of the emission rates of the deep levels. The results obtained from the application of these techniques to the study of the influences of the different implantation parameters are presented.

Characterization of intrinsic and impurity deep levels in ZnSe and ZnO crystals by nonlinear spectroscopy

Laser induced absorption and photoluminescence are used for the investigation of band states and deep levels (DLs) in ZnSe and ZnO bulk crystals. Interband two-photon and two-step absorption processes, both via DLs as intermediate (virtual and real, correspondingly) states, take place and give information about the main parameters of the DLs. The effects are investigated depending on doping and thermal treatment which change the contamination of native defects. The results illustrate the great possibilities of nonlinear spectroscopy methods in condenced matter science and especially in local defect study.

Effects of deep levels and Si-doping on GaInP material properties investigated by means of optical methods

Deep level characteristics in undoped and Si-doped Ga 0.51In 0.49P layers has been investigated using photocapacitance and photoluminescence (PL) methods. Ga 0.51In 0.49P layers were grown by metalorganic vapor-phase epitaxy in the temperature range 600–730 °C and with doping levels from 3.9 × 10 17 cm −3 to 1 × 10 19 cm −3 . A dominant deep level with an activation energy of about 0.98 eV was observered in all undoped samples. Further deep levels have been found with activation energies in the range 0.43–0.50 eV. Undoped samples grown at 650 °C exhibit the lowest trap concentration, with one remaining level at 0.89 eV only. A direct link of PL intensity to non-radiative recombination due to deep centers is demonstrated. Undoped samples exhibit the highest PL intensity at the growth temperature of lowest deep level density. Si doping suppresses the main deep level at ΔE T = 0.89 eV and results in an increase of PL intensity up to N D=2 × 10 18 cm −3 . Only deep levels in the energy range 0.41–0.50 eV were detectable. No DX-like effects due to Si doping were observed.

Deep level characterization of seeded physical vapor transport grown ZnSe

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Characterization of deep levels introduced by alpha radiation in n-type silicon

A detailed deep-level transient spectroscopy study of the characteristics of deep-level defects introduced by 5.48 MeV alpha particles in low-doped n-Si is reported. The deep-level characteristics studied include emission rate signatures, activation energies, capture cross sections and their temperature dependence, and defect concentrations and their spatial profiles. At least five deep levels in the upper-half band gap and two levels in the lower-half gap have been observed as a result of irradiation and characterized in detail. A systematic study of their generation rates up to a dose of about 3×1010 alpha particles/cm2 has been performed providing insights into the dose dependence of their formation mechanisms. Interesting room temperature transformation phenomena have been observed in our deep-level spectra during room temperature storage of the irradiated samples. Extensive isochronal thermal annealing measurements have been carried out to obtain data on the anneal-out characteristics of the radiation-induced deep levels and to identify these with the known defects wherever possible. A number of new annealed-in levels have been observed during this investigation. A detailed comparison with the published results is presented.

Deep Level Characterization and Passivation in Heteroepitaxial Inp

AbstractDeep levels in MOCVD grown p-InP on GaAs substrates have been investigated by Deep Level Transient Spectroscopy (DLTS). The effect of hydrogenation on the electrical activity of these levels has been studied through a combination of DLTS and Photoluminescence (PL) measurements. DLTS measurements indicate a drop of trap density from σ 5 × 1014 cm−3 to σ 1 × 1012 cm−3 after hydrogenation. Annealing at 400°C reactivated only the dopants, while temperatures above 600°C were necessary for deep-level reactivation. This combined with a logarithmic dependence on fill pulse time, indicate that at least one broad DLTS peak is associated with dislocations. The PL the DLTS results show that the dislocation related traps are passivated by hydrogen, preferentially over the dopants and that a wide annealing window exists for dopant reactivation.

Optical, photoelectrical, deep level and photorefractive characterization of CdTe:V

Characterization of different optical techniques, such as photo-induced current transient spectroscopy (PICTS), absorption, photoconductivity spectra and photorefractive wave mixing, of semi-insulating V-doped Cdytals prepared by the modified Bridgman method are presented. The aim of this joint research programme is to provide information which can lead to the understanding of the complex processes which determine photorefractive effects and to optimize the key parameters.