Parameters Of Deep Levels Research Articles

Spectroscopy of neutron irradiation induced deep levels in silicon by microwave probed photoconductivity transients

A contactless technique for simultaneous measurements of the carrier lifetime and the parameters of deep levels has been applied. This method is based on microwave probed pulsed photoconductivity (MW-PC) spectroscopy in the wavelength range between 0.5 and 4 μm. Several deep levels in the range of 0.2–0.6 eV have been resolved from spectral analysis of microwave probed photoconductivity amplitude variations in the samples of Si grown by magnetic field applied Czochralski (MCz) technology. An amplitude of the revealed MW-PC spectral steps showed an increase with neutron irradiation fluence indicating an enhancement of density of the specific defects. Simultaneous variations of recombination lifetime with fluence of the reactor neutrons from 10 12 to 3×10 16 n/cm 2 in the MCz Si samples have been examined. Recombination features of the irradiated and annealed MCz Si structures are discussed by comparing carrier recombination parameters and deep-level MW-PC spectral data with characteristics measured by deep-level-transient spectroscopy (DLTS) in the range of moderate irradiation fluences.

A deep-level transient spectroscopy study of transition metals in n-type germanium

The deep-level parameters of a number of technological relevant transition metals—Hf, Ti, Cr, Fe, Co and Ni—in n-type germanium have been studied by deep-level transient spectroscopy (DLTS). The metals have been introduced by ion implantation followed by annealing at 500 °C for 5 min. In most cases the annealing treatment is sufficient to remove the implantation point defects from the substrate, leaving only metal-related electron traps in the spectra. From the fact that for each metal, one (or more) peaks at a different position and with a different activation energy is observed, it is concluded that levels specific for the individual metals have been detected. This is further validated by the observation that the corresponding trap concentration increases with the implantation dose. In some cases, e.g. Hf, we believe that it is the first observation of the impurity-related deep electron traps in germanium.

Deep levels in the band gap of GaN layers irradiated with protons

Deep-level transient spectroscopy was used to study the parameters of deep levels in the band gap of epitaxial n-GaN layers after irradiaton of the Schottky barriers with 1-MeV protons to a dose of 1012 cm−2. A deep level EP1 with an activation energy of 0.085 eV was introduced by irradiation into the upper half of the GaN band gap. The introduction rate of the corresponding defect was found to depend on the bias voltage applied to the Schottky barrier during irradiation.

Copper-hydrogen complexes in silicon

Defect complexes of copper and hydrogen in silicon were studied in detail by deep-level transient spectroscopy. Floating-zone silicon, both n and p types, which had been copper doped during the growth, was hydrogenated by chemical etching. We determine the electrical parameters of substitutional copper and various copper-related deep levels. The concentration profiles after etching were measured and numerically fitted assuming a successive trapping of hydrogen atoms to substitutional copper. From our data we assign the Cu-related deep levels to different charge states of copper-hydrogen complexes containing one or two hydrogen atoms. For the ${\mathrm{CuH}}_{1}$ defect we measured deep levels at ${E}_{C}\ensuremath{-}0.36 \mathrm{eV}$ and ${E}_{V}+0.54 \mathrm{}\mathrm{eV}.$ The two levels at ${E}_{C}\ensuremath{-}0.25 \mathrm{eV}$ and ${E}_{V}+0.27 \mathrm{eV}$ we assigned to a ${\mathrm{CuH}}_{2}$ complex. We also have evidence for a neutral complex containing three or more hydrogen atoms. In p-type silicon, the capture radii for hydrogen by the substitutional copper have been determined to be 0.3 nm for the first and second hydrogen atoms and 1.0 nm for a third hydrogen atom. In n-type material these values are found to be higher: 0.7 nm, 0.9 nm, and 1.8 nm, respectively.

Study of polycrystalline diamond layers deposited from gas phase

Crystallite size in polycrystalline diamond layers with a grain size exceeding 3 μm are determined by the X-ray topography method with the use of a divergent beam from a point source. For layers with thicknesses in the range 80–700 μm deposited in SHF plasma and 1–40 μm obtained by the method of a hot filament, the size distribution of crystallites is obtained. Asterism of some spots on X-ray diffraction patterns from the diamond layers with thicknesses exceeding 100 μm showed plastic deformation of individual crystallites. The parameters of deep levels in the band gap of undoped high-resistance diamond layers and the acceptor-type defects with an activation energy higher than 1 eV are determined by the method of charge relaxation spectroscopy.

Radiation hardness of SiC ion detectors under relativistic protons

Schottky diodes based on 6H-SiC epitaxial films exposed to 1000 MeV protons at a dose of 3×1014 cm−2 have been studied by precision alpha spectrometry. Parameters of deep levels introduced by protons were determined by deep-level transient spectroscopy. The number of vacancies generated in proton tracks was found using TRIM software. The width of the space charge region and the hole diffusion length before and after irradiation were obtained by processing the alpha-spectrometry and capacitance measurements. Minor variations in the charge transport properties of epitaxial 6H-SiC detectors were observed.

Analysis of Admittance Data: Comparison of a Parametric and a Nonparametric Method

The thermal relaxation times are characteristic parameters of deep levels which can be calculated by the analysis of admittance data. The contributions of these characteristic parameters can be sharp or broadened. If sharp contributions are assumed the analysis procedure is called a parametric method. This procedure leads to a well-posed inverse problem but additionally the unknown number of discrete contributions must be determined. For broadened contributions a nonparametric method is used. This procedure leads to an ill-posed inverse problem but the number of contributions is determined automatically. Both kinds of analysis methods are compared with a Monte Carlo study on simulated admittance data. In addition, the parametric and nonparametric procedures are used to analyze experimental admittance data in order to obtain the deep levels and electrical properties of a semi-insulating GaAs Schottky diode.

Deep-level recombination spectroscopy in GaP light-emitting diodes

Deep-level parameters determined from an analysis of the differential coefficients of the forward-bias current-voltage curves are compared in the example of commercial GaP LEDs. It is shown that these parameters are suitable for deep-center diagnostics. The proposed measurements can be performed on semiconductor wafers in the industrial environment without sealing or dividing into individual crystals.

Determination of the parameters of deep levels from the relaxational delay of breakdown of a p-n junction

A technique for determining the deep-center parameters from the relaxational delay of avalanche breakdown of a p-n junction is investigated. The method implemented does not impose any restrictions on the relation between the concentration of the deep centers and that of the dopant impurities and can be used in those cases when the current-voltage characteristic of the sample is poorly monitored or the equivalent circuit of the p-n junction is complex. This may be a consequence of strongly compensated base regions, the presence of high-resistance layers, or imperfect ohmic contacts. Possibilities of the method are illustrated by the example of determining the parameters of the gold acceptor level in p+-n-n+ structures with high gold content (NAu=0.9Nd).

Determination of the parameters of deep levels using the differential coefficients of the current-voltage characteristics

Deep levels were determined in GaP light-emitting diodes using the differential coefficients of the current-voltage characteristics. The parameters determined by different methods showed agreement. The measurement conditions are such that the measurements can be made using wafers, which makes the proposed methods extremely promising.

Determination of the parameters of deep levels in semiconductors using nonstationary spectroscopy and low-frequency noise spectroscopy

A development of the activation-drift model is obtained. This enables the procedure for determining the parameters of deep levels in semiconductors using the data of nonstationary spectroscopy and low-frequency noise spectroscopy to be made more accurate and increases the reproducibility and reliability of the results of measurements.

Differential methods for determination of deep-level parameters from recombination currents of p-n junctions

Two techniques for determining the activation energies of centers that create deep levels in the space-charge region (SCR) of p-n junctions are developed on the basis of the Shockley-Read-Hall recombination model. The proposed techniques are based on a consideration of recombination currents in the SCR for a low injection level. The first technique involves a differential analysis of the reduced recombination rate ∂Rnp(U)/∂U and the second technique involves an analysis of the dependence Rnp2(U)/exp(qU/2kT). These techniques are used to analyze the current-voltage characteristics of gold-doped silicon p+-n diodes. The gold-related deep center activation energies obtained from the current-voltage characteristics are in good agreement with the available data in the literature.

The electrical assessment of Si1-xGex/Si heterostructures

A comprehensive electrical characterisation of the SiGe/Si heterostructures has been performed in the wide temperature range (10-270 K). For this study the structures fabricated by the ion implantation technique at three different substrate temperatures (room temperature, 150 C and 450 C) have been used. The presence and parameters of shallow and deep levels and the diode performance were studied as a function of the substrate temperature. The sample implanted at 450 C shows the best diode operation reflecting the higher quality of the surface silicon layer as compared to RT- and 150 C-implanted samples. For the first time the cryogenic TSCR technique has been applied to this system which makes it possible to investigate strain in the silicon layer due to SiGe layer formation.

Noise behaviour of semiinsulating GaAs particle detectors at various temperatures before and after irradiation

We investigated the noise behaviour of surface barrier detectors (double sided Schottky contact) made of Semiinsulating GaAs. Two types of measurements were performed: Equivalent Noise Charge (ENC) and noise power density spectra in a frequency range from 10 Hz to 500 kHz. The shape of the density spectra are a powerful tool to examine the physical origin of the noise, before irradiation it is dominated by Generation-Recombination processes caused by deep levels. Temperature dependent noise measurements reveal the deep level parameters like activation energy and cross section, which are also extracted by analyzing the time transients of the charge pulse from α-particles. After irradiation with protons, neutrons and pions the influence of the deep levels being originally responsible for the noise is found to decrease and a reduction of the noise over the entire frequency range with increasing fluence is observed.

Barrier Height of MIS-Tunnel Diode in Presence of Exponential Distribution of Deep Level Impurities

The barrier height of MIS tunnel diode is studied considering exponentially distributed deep level impurities. The space charge density has been calculated as a prior requirement for the evaluation of the barrier height and found sensitive to the deep level parameters. The barrier height of the device is found to increase with deep level density.

Correlation of radiation damage effects in high resistivity silicon detectors with results from deep level spectroscopy

Neutron irradiated high resistivity silicon detectors have been subjected to isochronous annealing in order to study the changes in the full depletion voltage and the leakage current. The corresponding evolution of bulk damage induced defect levels was monitored using the TSC method. A single TSC peak is found to be correlated with the transient decay of the depletion voltage which is observed after elevated temperature annealing of inverted detectors. In conjunction with deep level parameters obtained from an I-DLTS study and changes observed in the effective doping concentration and in the leakage current after exposure to high doses of /sup 60/Co-gammas, new insight is gained into the radiation induced device deterioration and the corresponding annealing behavior.

Deep level transient spectroscopy under conditions of current-carrier exchange between two allowed bands

Some characteristic features of deep level transient spectroscopy (DLTS) spectra of deep levels which effectively exchange current carriers with both allowed bands are studied. It is shown that the maxima of the peaks shift very little on the temperature scale, but analysis of the spectra by the conventional methods leads to errors in the determination of the parameters of the deep levels (ionization energies, capture cross sections). Several methods for determining these parameters more accurately are proposed and a numerical example of such an analysis of DLTS spectra is presented.

Deep energy levels and photoelectrical properties of thin cuprous oxide films

Thin films of cuprous oxide have been electrodeposited on molybdenum substrates. Some preliminary photoelectrical properties of two devices with semitransparent aluminum and gold top-electrodes have been measured. The device with a gold top-electrode exhibits a weak photovoltaic effect and a space charge limited current conduction mechanism in dark. The other device which had been annealed before the deposition of the aluminum top-electrode, exhibits a three-fold increase in resistivity and a marked difference in its temperature dependence of conductivity. From the temperature dependence of conductivity, two activation energies of 0.09 and 0.87 eV could be measured compared to 0.11 and 0.26 eV for the device with a gold electrode. Photoinduced current transient spectroscopy with a novel approach to the post-capture data analysis (additive double gate analysis) has been used in detection and the measurements of the parameters of several deep energy levels. These levels have activation energies in the range of 0.12 to 0.63 eV and capture cross-sections in the range of 10 −22 to 10 −12 cm 2. Using the role of the sample bias polarity on the identification of the type of the traps, one electron trap (surface state) and one hole trap (bulk state) could be identified among the five detected deep levels.

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.

On the recombination behaviour of iron in moderately boron-doped p-type silicon

The recombination lifetime and diffusion length of intentionally iron-contaminated samples were measured by the Surface Photo Voltage (SPV) and the Elymat technique. The lifetime results from these techniques for intentionally iron-contaminated samples were analysed, in particular for the aspect of the injection-level dependency of recombination lifetime. Based on theoretical considerations, a method for the analysis of deep-level parameters combining constant photon flux SPV and Elymat measurements has been developed. This method is based on a detailed numerical analysis of the Elymat technique, including the Dember electric field, the characteristics of the laser beam, the transport parameters of the semiconductor and multilevel Shockley-Read-Hall (SRH) recombination kinetics. The results of the numerical simulation are applied to the analysis of recombination lifetime measurements on intentionally iron-contaminated samples. We compared numerical simulations and experimental results from SPV and Elymat for p-type samples using the classical acceptor level atEv +0.1 eV and the donor level of FeB pairs atEc -0.3 eV as recombination centre. Better consistency in the interpretation of the results has been found in the doping range 1014–1016 cm−3 supposing theEc -0.3 eV level as predominant recombination centre. An attempt to extract the electron and hole capture cross-sections for this defect is made.