Capture Cross Section For Majority Carriers Research Articles

Analysis of defects dominating carrier recombination in CeO2 single crystal for photocatalytic applications

In photocatalytic water splitting and CO2 reduction, recently, cerium oxide (CeO2) has been widely investigated. Defects that can directly dominate carrier recombination are essential for the photocatalytic performance of CeO2. In this study, several photoluminescence (PL) peaks are observed on the (100) face of an undoped CeO2 single crystal, indicating the presence of defects. Moreover, we characterize carrier recombination using time-resolved photoluminescence (TR-PL) and microwave photoconductivity decay (μ-PCD) measurements. The temperature dependence of decay curves is the result of carrier trapping and emission at deep levels. These decay curves are observed separately using a 565 nm band-pass filter (BPF) based on the PL spectra. The trap energy level ( ET ) and majority carrier capture cross-section ( σT ) of each defect are also analyzed using rate equations to fit the experimental results. The temperature-dependent time constants are well reproduced by a recombination model using hole traps HTinfrared and HTvisible at ET of 0.76 and 0.55 eV from the conduction or valence band, with estimated σT of the order of 10−21 and 10−22 cm2 for without and with the BPF, respectively. These findings regarding the presence of multiple defects in a single crystal indicate the necessity to focus on defect control.

An all optical approach for comprehensive in-operando analysis of radiative and nonradiative recombination processes in GaAs double heterostructures

We demonstrate an all optical approach that can surprisingly offer the possibility of yielding much more information than one would expect, pertinent to the carrier recombination dynamics via both radiative and nonradiative processes when only one dominant deep defect level is present in a semiconductor material. By applying a band-defect state coupling model that explicitly treats the inter-band radiative recombination and Shockley–Read–Hall (SRH) recombination via the deep defect states on an equal footing for any defect center occupation fraction, and analyzing photoluminescence (PL) as a function of excitation density over a wide range of the excitation density (e.g., 5–6 orders in magnitude), in conjunction with Raman measurements of the LO-phonon plasmon (LOPP) coupled mode, nearly all of the key parameters relevant to the recombination processes can be obtained. They include internal quantum efficiency (IQE), minority and majority carrier density, inter-band radiative recombination rate (Wr), minority carrier nonradiative recombination rate (Wnr), defect center occupation fraction (f), defect center density (Nt), and minority and majority carrier capture cross-sections (σt and σtM). While some of this information is thought to be obtainable optically, such as IQE and the Wr/Wnr ratio, most of the other parameters are generally considered to be attainable only through electrical techniques, such as current-voltage (I-V) characteristics and deep level transient spectroscopy (DLTS). Following a procedure developed herein, this approach has been successfully applied to three GaAs double-heterostructures that exhibit two distinctly different nonradiative recombination characteristics. The method greatly enhances the usefulness of the simple PL technique to an unprecedented level, facilitating comprehensive material and device characterization without the need for any device processing.

Detection of a Molybdenum Acceptor Level in N-Type Silicon

The detection of Mo in n-type Si has been reported in only a few references. An unidentified peak was detected in an n-type epitaxial layer by DLTS with an activation energy and capture cross-section of 0.255 eV and 3.5 × 10−16 cm2, respectively. These results were consistent with measurements of n-type silicon implanted with Mo. A p-type epitaxial wafer was exposed to the same epitaxial growth environment resulting in the detection of the Mo-d level, thus confirming the Mo contamination. The change in the enthalpy of the capture of electrons into the unidentified level was 14 meV resulting in the majority carrier capture cross-section being determined to be 1.2 × 10−16 cm2 assuming a multi-phonon process. Using the activation energy and enthalpy change of capture cross-section data, the change in Gibbs free energy as a function of temperature was calculated to be Ec-0.269 eV. Poole-Frenkel effect measurements determined the deep level to be an acceptor-like state. The total change in entropy was determined to be 1k, the first reported total entropy change for an acceptor level of a 4d transition metal. The measured enthalpy energy was in reasonable agreement with the reported theoretical calculation of a substitution Mo-a deep level.

Modulation of electrical characteristics at a Ni-contaminated silicon grain boundary by engineering the metal precipitates

The effect of various forms of Ni contaminants on the electrical properties of a silicon grain-boundary (GB) formed by direct bonding technology has been investigated in this paper. It is found that compared to that of the clean GB, the density of interface states and their majority carrier capture cross-section for the as-contaminated GB is significantly increased, due to the interaction of Ni impurities with the interface defects. However, after Ni impurities precipitating at the GB by a post-annealing, the degrading effect of the Ni contamination on the GB electrical characteristics is reduced again. These results show the detrimental effect of a metal-contaminated GB on the electrical properties of multicrystalline silicon solar cells can be minimized by engineering the metal precipitate density and size distribution.

Electronic properties and dopant pairing behavior of manganese in boron-doped silicon

Boron-doped silicon wafers implanted with low doses of manganese have been analyzed by means of deep-level transient spectroscopy (DLTS), injection-dependent lifetime spectroscopy, and temperature-dependent lifetime spectroscopy. While DLTS measurements allow the defect levels and majority carrier capture cross sections to be determined, the lifetime spectroscopy techniques allow analysis of the dominant recombination levels and the corresponding ratios of the capture cross sections. Interstitial manganese and manganese-boron pairs were found to coexist, and their defect parameters have been investigated. In good agreement with the literature, this study identifies the defect level of manganese-boron pairs to be located in the lower half of the band gap at an energy level of Ev+0.55 eV with a majority carrier capture cross section of σp=3.5×10−13 cm2. The capture cross-section ratio was found to be k=σn∕σp=6.0. This implies that the previously unknown minority carrier capture cross section is σn=2.1×1012 cm2. Concerning the defect related to interstitial manganese, this study identifies the most recombination-active level to be located in the upper half of the band gap at EC−0.45 eV with a corresponding ratio of the capture cross sections of k=9.4. In addition, the temperature-dependent association time constant of manganese-boron pairs is determined to be τassoc,Mn=8.3×105 K−1 cm−3(T∕Ndop)exp(0.67 eV∕kBT) and found to differ from that for iron by a factor of 3 at room temperature, allowing this association time constant to be used as a fingerprint for a possible contamination with manganese. Also, the diffusion coefficient of interstitial manganese in silicon is determined from these experiments in a temperature range from 70 to 120 °C. It can be represented by the expression DMn=6.9×10−4 cm2 s−1 exp(−0.67 eV∕kBT).

Temperature Dependence of Carrier Recombination Lifetime in Si Wafers

The temperature dependence of carrier recombination lifetime for n‐ and p‐type Si wafers is measured by the photoconductivity decay method in a temperature range between room temperature and about 90 K. The carrier lifetime of as‐polished wafers has very weak temperature dependence, while the carrier lifetime decreases steeply with decreasing temperature for oxidized wafers. For all samples, a slow component appears in the photoconductivity decay curves after an initial fast decay at temperatures below 150 K. From a numerical simulation, we conclude that the decrease in the carrier lifetime with decreasing temperature is due to recombination through shallow recombination centers with an energy level within 0.15 eV from the bandedge, and that the slow component is due to minority carrier traps with a small majority carrier capture cross section.

Photoconductivity and Thermoelectric Power of ZnxCd1-xSe Films

Znx Cd1-x Se (0≤x≤1) films were deposited by two zone hot wall evaporation technique. X-ray diffraction analysis of the films indicated a predominant wurtzite structure for x<0.5, which changed to zinc blende structure for x>0.7. The films had a mixed structure for 0.5<x<0.7. The films were highly resistive (resistivity varying within 3 Ω· cm to 1.5×105 Ω· cm for 0≤x≤1.0) with partially depleted grains. The optical band gap (E g), determined from the reflectance measurements, indicated a direct transition with a bowing effect in E g versus x plot. The conductivity at low temperature (for x<0.6) could be explained by thermionic emission over the intercrystalline barrier, while for higher x quantum mechanical tunneling through the barrier became predominant. The variation of the barrier height (E bd) with the intensity of illumination was obtained from the photoconductivity measurements. The majority carrier capture cross-section ( 1-4×10-18 cm2) of the grain boundary traps ( 1×1011-1×1012 cm-2) was determined. The effect of the intercrystalline barrier on the thermoelectric power measurements was also considered.

Point defects in GaAs-Ga1-xAlxAs superlattices.

Deep-level transient spectroscopy has been applied to the study of deep localized levels in a series of uniformly n-type-doped GaAs-${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As superlattices having various periods. Using defects introduced by electron irradiation whose characteristics are well known in bulk GaAs and ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As, we demonstrate that their characteristics in these superlattices (energy-level position and majority-carrier capture cross section) can be reasonably predicted. We also show how the localization, which can be induced by the electric field, can be used to characterize native defects and eventually recognize them.

KINETICS OF THE CAPTURING FROM THE FREE MAJORITY CARRIER TAIL REGION AND MEASUREMENT OF THE MAJORITY CARRIER CAPTURE CROSS SECTION

We have discussed the kinetics of the capturing of freemajority tail by deep centres in semeconductors. We pointout that, the DLTS' signal is dicrectly proportional to the pulse width, if the DLTS' response region is restricted in the end of free-carrier tail vegion.This phenomenon may be used to measure the majority carrier capture cross section, in which the net shallow impurity concentration and the majority carrier capture cross section are both relatively wigh.

A simple circuit to aid direct measurement of capture cross sections of deep level impurities

An inexpensive and simple circuit to aid the direct measurement of majority carrier capture cross sections of impurity levels in the band gap of a semiconductor by the variable width filling pulse technique is presented. With proper synchronisation, during the period of application of the pulse, the device is disconnected from the capacitance meter to avoid distortion of the pulse and is reconnected again to the meter to record the emission transient. Modes of operation include manual triggering for long emission transients, repetitive triggering for isothermal and DLTS measurements and the DLTS mode which is to be used with signal analysers that already provide a synchronising pulse for disconnection.

Improvements in the determination of interface state density using deep level transient spectroscopy

Deep level transient spectroscopy (DLTS) in the current transient mode has been applied to the measurement of the trap density at the silicon-silicon dioxide interface. Application of Shockley–Read–Hall theory to the analysis of DLTS data indicates that if the energy dependence of the majority carrier capture cross section is strong, then it is necessary to take it into account if accurate interface state density values are to be obtained. We have used the small pulse trap filling technique to estimate the degeneracy factor and measure the capture cross sections of the interface states, and then applied this information in the calculation of the interface trap density from a conventional large pulse DLTS temperature scan. Very good agreement is obtained with the values extracted from high-low frequency capacitance-voltage measurements.

Photocurrent deep level transient spectroscopy in silicon

Photocurrent deep level transient spectroscopy (PCDLTS) is investigated as a technique for the detection of centers in the minority half of the band gap. The photocurrent and resulting peak shapes are analyzed and compared with experimental results obtained from gold-doped silicon diodes illuminated with different wavelength sources. It is shown that by suitable selection of the photon wavelength, reliable detection of levels in the minority half of the band gap is possible in long lifetime material. However, for centers with a large ratio of majority carrier capture cross section to minority carrier capture cross section, their detection in short lifetime material is likely to be more difficult, unless the material is thinned down and used with an appropriately matched photon source.

Defect levels in chromium-doped silicon

The transient capacitance technique has been used to study the chromium-related levels in the silicon band gap. Chromium was diffused at temperature of 1100 and 1150°C for 0.5 and 3 hr. Five different levels at E c −0.11 eV, E c −0.21 eV, E c −0.28 eV, E c −0.36 eV and E c −0.45 eV were obtained from the Arrheniu plots of the electron thermal-emission rates. The number of levels in the upper half of the band gap decreased from five to two with an increase of Cr-diffusion period. Two levels were located at E c −0.20 eV (donor) and E c −0.43 eV (acceptor). A donor level was also observed at E v + 0.25 eV. The donor level was not affected by the diffusion condition. The majority carrier capture cross sections of the three dominant levels have been measured by the transient capacitance technique modified by the pulse transformer. The values were σ n = 4.1 × 10 −15 cm 2 for the upper donor at E c −0.20 eV, σ n = 2.0 × 10 −16 cm 2 for the acceptor at E c −0.43 eV and σ p = 9.1 × 10 −18 cm 2 for the lower donor at E v + 0.25 eV, and were independent of temperature. The three dominant levels are due to distinct chromium centers.

The Electronic States of Some Metal Impurities in Germanium

Capacitance spectroscopy measurements of the energy levels and majority carrier capture cross sections of deep impurity states associated with S, Zn, Pb and Bi in Ge are presented. Similarities in the electrical properties of these elements with other deep impurities in Ge are discussed.

Admittance spectroscopy of deep levels in Hg1−xCdxTe

We report the application of diode admittance spectroscopy in characterizing traps in Hg1−xCdxTe. Measurements performed on n+-p junction photodiodes have identified a hole trap located 0.16 eV above the valence band in x=0.305 liquid-phase-epitaxy-grown material and a single hole trap located 0.046 eV above the valence band in x=0.219 bulk-grown material. Measurements of trap density and majority-carrier capture cross section have also been carried out, with results suggesting hole capture at a neutral trapping center. Trap energies determined by the admittance spectroscopy technique were found to be in good agreement with lifetime-versus-temperature data analyzed in terms of a single Shockley-Read recombination center.

Electrical characteristics of sputtering-induced defects in n-type silicon

The electrical characteristics of the sputtering induced defects have been studied using the DLTS measurements. A band of defect states located at Ec-0.3 eV to Ec-0.5 eV was found. The measured capture cross-section for majority carriers at this band is 1.3 × 10−19 cm2. The concentration profile of this band of defects decreases exponentially from the surface. This initial concentration of the defects near the surface of a sputtered platinum silicide diode is extrapolated to 7 × 1017 cm−3. The defects anneal out after 10 min of annealing time at 400 °C.

Carrier generation at the Si-SiO2 interface under pulsed conditions

A simple analysis is given of the displacement current transient following an application of a depleting pulse to the gate of a metal-insulator-semiconductor capacitor. It is shown that a plot of the current vs reciprocal time may be used to obtain the surface state density near midgap, the majority-carrier capture cross section, and the bulk minority-carrier lifetime. Experimental results for a typical MOS capacitor are presented.

Expedient method of obtaining interface state properties from MIS conductance measurements

In obtaining accurate values of interface state density and majority carrier capture cross section for SiSiO 2 interfaces from MIS capacitor admittance measurements, it has been necessary to analyze considerable data. The reason for this is a new effect described previously, namely the large dispersion of interface state time constant caused by fluctuations of surface potential. A computer program briefly outlined here has been developed which calculates interface state properties from a minimum of measured input data. The data required are: (i) low frequency capacitance vs. bias to get surface potential, (ii) admittance vs. frequency at fixed bias to get standard deviation of surface potential, and (iii) admittance vs. bias at two frequencies to get interface state density and majority carrier capture cross section vs. energy. A listing of the computer program and a description of how to use it can be obtained on request.