Electrically active defects in SiC Schottky barrier diodes

The electrical properties of deep-level defects in real packaged SiC Schottky barrier rectifiers were studied by deep level transient spectroscopy (DLTS). One deep-level trap with an activation energy in the 0.29–0.30 eV range was revealed to be present in all the tested samples. The electrical characteristics of the trap indicate it is probably attributed to dislocations or to metastable defects, which can be responsible for discrepancies observed in I-V characteristics (see Ref. [2]).     

Deep level transient spectroscopy of hole traps related to CdTe self-assembled quantum dots embedded in ZnTe matrix

The capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements have been made on a Schottky Ti-ZnTe (p-type) diode containing CdTe self-assembled quantum dots (QD) and control diode without dots. The C-V curve of the QD diode exhibits a characteristic step associated with the QD states whereas the reference diode shows ordinary bulk behavior. A quasistatic model based on the self-consistent solution of the Poisson's equation is used to simulate the capacitance. By comparison of the calculated C-V curve with the experimental one, hole binding energy at the QD states is found to be equal about 0.12 eV. The results of DLTS measurements for the sample containing QDs reveal the presence of a low-temperature peak which is not observed for the control diode. Analysis of its behavior at different bias conditions leads to the conclusion that this peak may be related to the hole emission from the QD states to the ZnTe valence band. Its thermal activation energy obtained from related Arrhenius plot equals to 0.12 eV in accordance with the energy obtained from the Poisson's equation. Thus based on the C-V and DLTS studies it may be concluded that the thermal activation energy of holes from the QD states to the ZnTe valence band in the CdTe/ZnTe QD system is equal about 0.12 eV.     

A computer controlled system for transient capacitance measurementsof deep levels in semiconductor

A computer-controlled system was set up for the measurement of deep levels in semiconductors. It has a custom-designed interface card to establish communications between necessary instruments and a personal computer. The card enables the system to have a maximum sampling rate of 20000 sample/s. Comparisons were made between the present system and those of other workers. The system is very versatile as its function is solely determined by software programs; different techniques like DLTS (deep-level transient spectroscopy) and TSCAP (thermally stimulated capacitance measurement) can be used on the same setup by developing different programs. The system was applied to the study of deep traps in Si produced as a result of pulsed-laser irradiation. An electron deep trap level of 0.22 eV below the conduction band was found     

A compact microcomputer-based deep level transient spectroscopymeasurement system

A specifically designed system for deep-level transient spectroscopy (DLTS) measurement is described. It is compact and fully automated, can measure all the spectra in just one temperature scan, and permits simultaneous analysis of two devices. The user sets up the measurement conditions with a reduced number of commands. This makes the system very flexible and versatile. A self-scaled gain output amplifier has been incorporated to provide the maximum DLTS signal amplitude compatible with the input range of the analog-to-digital (A/D) converter. This self-scaling allows the detection of traps with a large amplitude range. Up to 90 sampling times can be selected for each transient. To improve the signal-to-noise ratio (SNR), as many as 32768 scans may be accumulated for averaging. Improvements as high as 45 dB have been used to characterize deep centers in AlGaAs/GaAs devices grown by liquid-phase and molecular-beam epitaxies     

Forward-current-generated donor centers in high-voltage 4H-SiC based <Emphasis Type="Italic">p-i-n</Emphasis> diodes

High-voltage diodes based on silicon carbide of 4H polytype (4H-SiC) have been studied by the deep-level transient spectroscopy (DLTS) method. It is established that the passage of forward current leads to the activation of a donor center with an activation energy of E _c − 0.2 eV and an electron capture cross section of σ _n ∼ 2.0 × 10⁻¹⁵ cm². The DLTS measurements reveal the appearance of this center upon the transfer of a very small charge through the diode, under the conditions where the forward voltage drop on the diode remains almost unchanged. A possible nature of the observed phenomenon is discussed.     

On the use of the matrix pencil method for deep level transientspectroscopy: MP-DLTS

A new approach to capacitance transient analysis, based on the matrix pencil (MP) method, is proposed for deep level transient spectroscopy (DLTS) (MP-DLTS). The MP method offers the least statistical variance of the estimates in the presence of noise. Simulation tests have shown this method to lead to a significant improvement in DLTS resolution even for low trap concentrations. Its noise sensitivity and resolution are quantified and compared with five different DLTS analysis techniques. The MP-DLTS method is found to outperform both DLTS spectrum and direct transient analysis techniques. An experimental investigation of the electrically active defects induced by a germanium preamorphization step prior to dopant implantation was undertaken using the MP-DLTS method. Two electron traps were detected in all samples and characterized     

Localized states in the active region of blue LEDs related to a system of extended defects

Blue light-emitting diodes (LEDs) based on InGaN/GaN quantum wells (QWs) with different characters of the system of extended defects (SEDs) threading through the active region have been studied using the current-voltage (I–U), capacitance-voltage (C–V), and deep-level transient spectroscopy (DLTS) measurements in the dark and under illumination with white light in a temperature range from 100 to 450 K. The DLTS curves exhibit broad E1 and E2 peaks with amplitudes dependent on the illumination. This behavior can be explained assuming the presence of localized states related to SEDs in the active region of the LED. The LEDs with more developed SEDs are characterized by a greater concentration of donor-type traps, which leads to an increase in the density of free charge carriers in QWs, which screen the electron-hole interaction. This circumstance can be among the factors responsible for a severalfold decrease in the quantum efficiency of such LEDs.     

Neutron-irradiation-induced defects in germanium: A Laplace deep level transient spectroscopy study

Deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS (L-DLTS) and L-DLTS combined with uniaxial stress have been used in this work for characterization and identification of electrically active defects induced in Sb-doped germanium crystals by irradiation with fast neutrons. The samples were irradiated with relatively small doses of neutrons (≤5 × 10¹¹ cm⁻²) in order to produce uniformly distributed damage and to detect small defect clusters. It is found that for such low neutron doses in many respects the damage produced is similar to that resulting from electron irradiation. Vacancy-antimony (V-Sb) pairs uniformly distributed in the sample bulk are the dominant defects observed in the DLTS spectra. It is inferred from the L-DLTS measurements under application of uniaxial stress that the V-Sb pair has a trigonal symmetry in the doubly negatively charged state. It is argued that an electron trap with the activation energy for electron emission of 0.1 eV is related to an acceptor state of a small vacancy cluster located in highly damaged regions of the neutron-irradiated samples. L-DLTS measurements under application of uniaxial stress indicate that the symmetry of the defect is low, monoclinic-I, C_1h point group, or lower. Environment-induced broadening of the L-DLTS signal due to this centre prevents precise determination of the defect symmetry.     

Relaxation spectroscopy of deep levels in semiconductors: Laplace-DLTS method

Deep level transient spectroscopy (DLTS) is among the main methods used to determine the parameters of electrically active centers of charge localization in semiconductors. In order to increase the accuracy and adequacy of DLTS data, we propose a modified approach based on the application of an inverse Laplace transform. Using the proposed Laplace-DLTS method, it is possible to determine the parameters of centers with close carrier emission coefficients, which cannot be done using the traditional DLTS technique.     

Parameter evaluation in automated digital deep-level transientspectroscopy (DLTS)

A method of directly evaluating the activation energy ΔE, capture cross section σ, and density N_T, of deep-level traps from the pulsed reverse bias capacitance transient is described. The main advantages of this technique are that it requires only a single temperature scan, and it can resolve nonexponential transients due to closely-spaced energy levels. The test samples used for this paper consisted of Schottky diodes fabricated on nonirradiated and 1-MeV electron-irradiated n-type VPE (vapor-phase epitaxy) GaAs wafers. The well known EL2 trap was identified with ΔE of 0.81 eV, and σ _n of 1.0×10^-13 cm² for the nonirradiated sample. These values were found to be in good agreement with published data using established, conventional DLTS techniques. For the irradiated samples a nonexponential capacitance transient was found in the EL2 range of temperatures. The discussed technique was able to resolve two closely spaced deep levels lying at E_c-0.81 eV and E_c-0.84 eV, and with capture cross sections of 1.5×10^-13 cm² and 2.5×10^-12 cm², respectively     

Laplace transform deep level transient spectroscopy: new insight into defect microscopy

Abstract

It is demonstrated that a resolution of deep level transient spectroscopy (D LTS) can be improved using the Laplace transform method for the emission rate analysis. Considerable confidence in this approach was gained through numerous tests carried out on two numerical algorithms used for the calculations as well as through measurements of a selection of well characterised point defects in various semiconductors. For each of these defects conventional DLTS gives broad featureless lines, whereas Laplace DLTS reveals afine structure in the emission process producing the spectra.

MST/3321     

Defect engineering for high-power 780 nm AlGaAs laser diodes

Defect engineering is carried out to determine optimum growth conditions for highly reliable high-power 780 nm AlGaAs laser diodes (LDs) using deep level transient spectroscopy (DLTS). The DLTS results reveal that the defect density of the Al_0.48Ga_0.52As cladding layer depended heavily on growth temperature and AsH₃ flow but that of the Al_0.1Ga_0.9As active layer depended mostly on the growth rates of the active layer. As a result of layer optimization at growth condition by DLTS, a record high output power of 250 mW was obtained at an operating current as low as 129.6 mA under room temperature continuous wave (CW) operation.     

Investigation of polarization fatigue induced deep level transient spectroscopy in lead zirconate titanate thin film

Deep level transient spectroscopy (DLTS) in pulsed laser deposited lead zirconate titanate (Pb(Zr_0.52Ti_0.48)O₃ thin film grown on LSCO (La_0.5Sr_0.5)O₃ bottom electrode and LaAlO₃ substrate has been investigated. The transient capacitance and the deep level energy inside the energy band gap are correlated with the number of bipolar switching cycles. It was found that both of them increase with the number of switching cycles.     

Computerized digitizing technique for DLTS measurements

An enhanced version of an algorithm developed by Maguire and Marshall in their computerized DLTS system is presented. Improvements consist of introducing analysis of partial processing of digitized transients by deleting the initial part, which usually includes the loading transient caused by the measurement circuit RC constant. Also, a method to calculate trap concentration without using correlation functions is added. Some of the limitations involved with the use of this algorithm are also discussed     

双层超弹性铰链展开冲击分析与优化

超弹性铰链依靠自身大挠度弹性折叠存储的弹性势能实现弹性展开,集驱动、旋转和锁定于一体。研究了双层超弹性铰链展开冲击性能,提出了降低双层超弹性铰链展开冲击优化方法。为了确保有限元模型的准确性,搭建实验平台对双层超弹性铰链进行动力学展开性能测试,基于实验结果对有限元模型进行修正。采用正交法试验设计建立展开冲击特性代理模型。以展开冲击角度和锁定时间最小为目标函数,采用改进的非支配遗传算法对双层超弹性铰链进行参数化优化设计,得到最优结构尺寸。对最优结构尺寸进行有限元展开分析,误差不大于5.008%,表明代理模型准确性。最优非等厚度与等厚度双层超弹性铰链对比,发现前者冲击角度和锁定时间分别降低52.154%和29.104 %,优化后结构的冲击得到明显改善。通过参数研究发现,展开冲击对外侧带簧厚度较为敏感,锁定时间随带簧厚度增加表现出先减少后增大的趋势。     

Deep levels induced by InAs/GaAs quantum dots

Self-organised InAs/GaAs quantum dots (QDs) were formed by molecular beam epitaxy using the Stranski–Krastanov growth mode. Deep-level transient spectroscopy as well as secondary ion mass spectrometry have been used to characterise structures containing the QDs. DLTS depth profiling procedures indicate that deep level-related defects are localised in GaAs in the vicinity of the QD plane. For the first time, we report the presence of a deep level-related trap with an extremely high thermal activation energy of E_c − 1.03 eV. An electron trap at E_c − 0.78 eV can be identified as the well-known level related to the EL2 family. We conclude that a third trap revealed at E_c −0.57 eV is the familiar PL killer related to the intrinsic point defect-oxygen complex. The latter is confirmed by results of the SIMS study, which indicates that the amount of oxygen accumulated at the InAs/GaAs heterointerface is increased. This paper demonstrates that the EL2 and oxygen-related deep-level centers occur by the presence of InAs/GaAs QDs. We present the hypothesis that deep states could be a factor limiting the efficiency of QD-based devices.     

Electrical characterization of deep levels existing in fully implanted and rapid thermal annealed p+n InP junctions

In this paper, the deep levels existing in fully implanted and rapid thermal annealed p⁺n junctions obtained by Mg/Si or Mg/P/Si implantations on nominally undoped n-type InP substrates were detected and characterized by the correlation of two electrical techniques: deep level transient spectroscopy (DLTS) and capacitance–voltage transient technique (CVTT). Two ion implantation-induced deep levels (at 0.25 and 0.27 eV below the conduction band) were detected by DLTS. Several characteristics of these traps were derived from CVTT measurements, paying special attention to their physical nature.     

Oxygen defects in irradiated germanium

The defects present in oxygen-rich irradiated germanium have been extensively characterised from an experimental point of view. Here, we summarise recent theoretical findings obtained using the cluster method and discuss their relation with the experimental data. In order to find a microscopic interpretation of the reactions taking place in this material upon annealing up to 400°C, we performed nudged elastic band (NEB) calculations of the migration and dissociation paths of VO, as well as a modelling of other oxygen-related complexes that are expected to form in this temperature range. Energy barriers of 1.5 (1.1) eV and 1.2 (0.9) eV for the dissociation and migration of the neutral (negatively charged) VO defect are found. We compare these with the activation energies estimated from the analysis of Hall effect, deep level transient spectroscopy (DLTS) and infra-red (IR) spectroscopy annealing data reported in literature.     

Fit of first order thermoluminescence glow peaks using the Weibull distribution function

A new thermoluminescence glow curve deconvolution (GCD) function is introduced which accurately describes first order thermoluminescence (TL) curves. The new GCD function is found to be accurate for first order TL peaks with a wide variety of the values of the TL kinetic parameters E and s. The 3-parameter Weibull probability function is used with the function variables being the maximum peak intensity (Im), the temperature of the maximum peak intensity (Tm) and the Weibull width parameter b. An analytical expression is derived from which the activation energy E can be calculated as a function of Tm and the Weibull width parameter b. The accuracy of the Weibull fit was tested using the ten reference glow curves of the GLOCANIN intercomparison program and the Weibull distribution was found to be highly effective in describing both single and complex TL glow curves. The goodness of fit of the Weibull function is described by the Figure of Merit (FOM) which is found to be of comparable accuracy to the best FOM values of the GLOCANIN program. The FOM values are also comparable to the FOM values obtained using the recently published GCD functions of Kitis et al. It is found that the TL kinetic analysis of complex first-order TL glow curves can be performed with high accuracy and speed by using commercially available software packages.     

Deep level transient spectroscopy study for the development of ion-implanted silicon field-effect transistors for spin-dependent transport

A deep level transient spectroscopy (DLTS) study of defects created by low-fluence, low-energy ion implantation for development of ion-implanted silicon field-effect transistors for spin-dependent transport experiments is presented. Standard annealing strategies are considered to activate the implanted dopants and repair the implantation damage in test metal-oxide-semiconductor (MOS) capacitors. Fixed oxide charge, interface trapped charge and the role of minority carriers in DLTS are investigated. A furnace anneal at 950 °C was found to activate the dopants but did not repair the implantation damage as efficiently as a 1000 °C rapid thermal anneal. No evidence of bulk traps was observed after either of these anneals. The ion-implanted spin-dependent transport device is shown to have expected characteristics using the processing strategy determined in this study.