Majority Carrier Trap Research Articles

Trap-mediated bipolar charge transport in NiO/Ga2O3 p+-n heterojunction power diodes

The construction of p-NiO/n-Ga2O3 heterojunction becomes a popular alternative to overcome the technological bottleneck of p-type Ga2O3 for developing bipolar power devices for practical applications, whereas the identification of performance-limiting traps and the bipolar transport dynamics are still not exploited yet. To this end, the fundamental correlation of carrier transport, trapping and recombination kinetics in NiO/β-Ga2O3 p+-n heterojunction power diodes has been investigated. The quantitative modeling of the temperature-dependent current-voltage characteristics indicates that the modified Shockley-Read-Hall recombination mediated by majority carrier trap states with an activation energy of 0.64 eV dominates the trap-assisted tunneling process in the forward subthreshold conduction regime, while the minority carrier diffusion with near-unity ideality factors is overwhelming at the bias over the turn-on voltage. The leakage mechanism at high reverse biases is governed by the Poole-Frenkel emissions through the β-Ga2O3 bulk traps with a barrier height of 0.75 eV, which is supported by the identification of majority bulk traps with the energy level of EC − 0.75 eV through the isothermal capacitance transient spectroscopic analysis. These findings bridge the knowledge gap between bipolar charge transport and deep-level trap behaviors in Ga2O3, which is crucial to understand the reliability of Ga2O3 bipolar power rectifiers.

Majority and Minority Carrier Traps in Manganese as‐Implanted and Postimplantation‐Annealed 4H‐SiC

Ion implantation of amphoteric impurities, like vanadium (V) or manganese (Mn), can be employed for the formation of resistive layers in 4H‐SiC. Such layers can then be used for device isolation, in order to reduce the parasitic capacitance. While V implantation can form thermally stable resistive layers, not much is known on Mn implantation. Herein, Mn ion‐implanted samples are electrically characterized by means of capacitance–voltage, deep‐level transient spectroscopy, and current–voltage measurements. Two ion implantation schedules are carried out: single‐energy and multiple‐energy ions so to have Gaussian and box‐shaped Mn and related ion damage profiles, respectively—the former with a maximum concentration in the low 1016 cm−3 and the latter with a Mn plateau of 1017 cm−3. It is found that several majority carrier traps, in the 0.4–1.7 eV range below the conduction band edge, and two minority carrier traps arise after implantation and after postimplantation annealing in the 1000–1800 °C temperature range. The detected traps, as well as previous reports in the literature, show that most of them can be associated with the intrinsic defects. Box‐profile implanted layers show resistivity values in the ≈106 Ω cm after heat treatments of, at least, 1600 °C.

Majority and Minority Charge Carrier Traps in n-Type 4H-SiC Studied by Junction Spectroscopy Techniques

In this review, we provide an overview of the most common majority and minority charge carrier traps in n-type 4H-SiC materials. We focus on the results obtained by different applications of junction spectroscopy techniques. The basic principles behind the most common junction spectroscopy techniques are given. These techniques, namely, deep-level transient spectroscopy (DLTS), Laplace DLTS (L-DLTS), and minority carrier transient spectroscopy (MCTS), have led to recent progress in identifying and better understanding the charge carrier traps in n-type 4H-SiC materials.

A Simple Method to Differentiate between Free‐Carrier Recombination and Trapping Centers in the Bandgap of the p‐Type Semiconductor

In this research, the ranges of the localized states in which the recombination and the trapping rates of free carriers dominate the entire transition rates of free carriers in the bandgap of the p‐type semiconductor are described. Applying the Shockley–Read–Hall model to a p‐type material under a low injection level, the expressions for the recombination rates, the trapping rates, and the excess carrier lifetimes (recombination and trapping) were described as functions of the localized state energies. Next, the very important quantities called the excess carriers’ trapping ratios were described as functions of the localized state energies. Variations of the magnitudes of the excess carriers’ trapping ratios with the localized state energies enable us to categorize the localized states in the bandgap as the recombination, the trapping, the acceptor, and the donor levels. Effects of the majority and the minority carriers’ trapping on the excess carrier lifetimes are also evaluated at different localized energy levels. The obtained results reveal that only excess minority trapping affects the excess carrier lifetimes, and excess majority carrier trapping has no effect.

Current-Mode Deep Level Spectroscopy of Vanadium-Doped HPSI 4H-SiC

SiC has currently attracted the interest of the scientific community for qubit applications. Despite the importance given to the properties of color centers in high-purity semi-insulating SiC, little is known on the electronic properties of defects in this material. In our study, we investigated the presence of electrically active levels in vanadium-doped substrates. Current mode deep level transient spectroscopy, carried out in the dark and under illumination, together with 1-D simulations showed the presence of two electrically active levels, one associated to a majority carrier trap and the other one to a minority carrier trap. The nature of the detected defects has been discussed in the light of the characterization performed on low-energy electron irradiated substrates and previous results found in the literature.

Influence of Charge Transport Layers on Capacitance Measured in Halide Perovskite Solar Cells

Summary Capacitance-based techniques have been used to measure the electrical properties of halide perovskite solar cells (PSCs) such as defect activation energy and density, carrier concentration, and dielectric constant, which provide key information for evaluating the device performance. Here, we show that capacitance-based techniques cannot be used to reliably analyze the properties of defects in the perovskite layer or at its interface, because the high-frequency capacitance signature is due to the response of charge carriers in the hole-transport layer (HTL). For HTL-free PSCs, high-frequency capacitance can be considered as the geometric capacitance for analyzing the dielectric constant of the perovskite layer because there is no trapping and de-trapping of charge carriers in the perovskite layer. We further find that the low-frequency capacitance signature can be used to calculate the activation energy of the ionic conductivity of the perovskite layer, but the overlapping effects with charge transport materials must be avoided.

Емкостная спектроскопия гетероэпитакиальных AlGaAs/GaAs p-i-n-структур

Temperature dependences of capacitance-voltage (C−V) characteristics and deep-level spectra of the graded highvoltage AlxGa1−xAs p0 −i−n0 junction grown by liquid-phase epitaxy via autodoping with background impurities were investigated. The changes of the C−V characteristics at varied measurement temperature and optical illumination demonstrated that the p0-, i-,n0-type layers in the AlxGa1−xAs under study contain bistable DX centers. In spectra of deep-level transient spectroscopy (DLTS), measured at various bias voltages Vr and filling pulses Vf , a positive DLTS peak is observed for the n 0 -type layer with thermal activation energy Et = 280 meV and electron-capture cross-section σn = 3.17 · 10−14 cm2, which is unusual for a majority-carrier trap. This peak is related to the negatively charged state of the Se/Te donor impurity, which is a bistable DX center with negative correlation energy U.

On the Transient Negative Photoconductance in <italic>n</italic>-type Czochralski Silicon

A transient negative photoconductance phenomenon is observed in n -type Czochralski silicon wafers. After a pulsed light excitation, the measured photoconductance drops to negative values and then increases to the original zero. The paper details how transient negative photoconductance is predicted by the Shockley–Read–Hall rate equations for a system of two defects. For this to occur, one defect must act as a majority carrier trap, and the other must be a relatively faster recombination channel. The specific conditions of these defects for a negative photoconductance to occur are derived analytically. Numerical modeling of this system shows good agreement with the experimental results. Finally, a method to extract the trap parameters from negative photoconductance for a sample with temperature-independent capture cross sections is demonstrated.

I–V curve hysteresis induced by gate-free charging of GaAs nanowires' surface oxide

The control of nanowire-based device performance requires knowledge about the transport of charge carriers and its limiting factors. We present the experimental and modeled results of a study of electrical properties of GaAs nanowires (NWs), considering their native oxide cover. Measurements of individual vertical NWs were performed by conductive atomic force microscopy (C-AFM). Experimental C-AFM observations with numerical simulations revealed the complex resistive behavior of NWs. A hysteresis of current-voltage characteristics of the p-doped NWs as-grown on substrates with different types of doping was registered. The emergence of hysteresis was explained by the trapping of majority carriers in the surface oxide layer near the reverse-biased barriers under the source-drain current. It was found that the accumulation of charge increases the current for highly doped p+-NWs on n+-substrates, while for moderately doped p-NWs on p+-substrates, charge accumulation decreases the current due to blocking of the conductive channel of NWs.

Hierarchically constrained carrier dynamics in red-LED illuminated type-II InAs/GaSb superlattices

We report on positive and negative persistent photo-effects observed in some red light emitting diode (LED)-illuminated type-II InAs/GaSb superlattices (SLs) grown on a p-type GaSb. By analyzing the time dependence of the transverse resistance during and after the illumination, we show that the rise and decay curves are logarithmic, a behavior which points to hierarchically constrained carrier dynamics. Accordingly, negative persistent effects are explained by diffusion and trapping of photo-excited carriers in the p-type buffer layer and their subsequent tunneling back to the SL. On the other hand, positive persistent effects are explained by a low density of majority-carrier trapping centers in the buffer layer. Hence, persistent photo-effects upon red-LED irradiation provide a diagnostic of the quality of the superlattice-buffer interface.

Dry and Wet Processed Interface Layer in Ge/High-K Devices Studied by Deep Level Transient Spectroscopy

In this work, dry and wet processed interface layer quality in Ge/High-K MOS structure (1) were studied by deep level transient spectroscopy (DLTS) (2). The MOS devices were pulsed from mid-bandgap to accumulation region, then return to mid-bandgap to obtain the majority carrier trap emission information. Figure 1(a-c) shows the DLTS data for three corresponding interface treatment. The Arrhenius plots are shown in Figure 1(d). Comparing the DLTS spectrum, it can be concluded that dry processes have discrete border traps at the interface (H3 and H5). No such traps at the interface of wet processed MOS devices were observed. For all three samples, however, interface like traps were detected (H1, H2, H4). The defects density was estimated by Eq. (1), where is obtained from CV plot using measured . The results suggest that it is around 1013 cm-2/eV for all three samples. This further confirms that the origin of interface state density, Ditobserved for these samples (1) are mainly due to these traps. The time constants in the order of milliseconds were also previously observed. Table I summarizes the Energy levels and cross-sections of these traps. (1) Acknowledgement:The authors would like to thank K. Tapily, R. D. Clark, S. Consiglio, C. S. Wajda, and G. J. Leusink of TEL Technology Center, Albany, NY, for supplying devices and helpful discussions. Table I. Arrhenius plot fitting results H1 H2 H3 H4 H5 ET-EV (eV) 0.16 0.1 0.18 0.04 0.45 (cm2)a 6.3×10-17 1.3×10-19 3.6×10-19 5.8×10-21 8.6×10-13 a Cross section is calculated by assuming = 1020 cm-2 s-1K-2. Figure 1. Deep level transient spectrum of (a) simple chemical oxidation (Chemox), (b) chemical oxide removal (COR) followed by 1 nm oxide by slot-plane-antenna (SPA) plasma (COR&SPAOx), (c) COR followed by vapor O3 treatment (COR&O3). (d) shows the Arrhenius plots for all three samples.

Detection of minority carrier traps in p-type 4H-SiC

Contrarily to the case of n-type 4H-SiC, very little is known about the presence of minority carrier traps in p-type epilayers. In this study, we performed the electrical characterization of as-grown, electron irradiated, and thermally oxidized p-type 4H-SiC, by using minority carrier transient spectroscopy. Four minority carrier traps are reported in 1.6–2.3 eV energy range above the valence band edge (EV). Particular emphasis is given to the mid-gap minority carrier trap (EH6∕7) and to its correlation to an energetically close mid-gap majority carrier trap (HK4).

Minority Carrier Transient Spectroscopy of As-Grown, Electron Irradiated and Thermally Oxidized p-Type 4H-SiC

A total of nine electrically active levels have been detected in as-grown and electron irradiated p-type 4H-SiC epilayers. These traps are found in the 0.32-2.26 eV energy range, above the valence band edge (EV). Of these, six are majority carrier traps whereas three are minority carrier traps. We found that thermal oxidation affects the concentrations of two midgap levels, the majority carrier trap, labeled HK4 and the minority carrier trap identified as EH6/7. The analysis of the irradiation energy and dose dependence of the concentration of these two traps, rules out the possibility that they may share the same origin.

Boron Ion Interaction with pnp Bipolar Power Transistor and Displacement Damage Effects on its Electrical Characteristics

Bipolar junction transistors used in switching and amplification applications is examined for their electrical performance after irradiation with 60 MeV boron ions of different fluence. Unirradiated device base current is 5.97×10-5 A while it is 9.03×10-4 A after irradiation with a fluence of 1×1012 ions/cm2. For unirradiated device collector current is 1.22×10-3 A and is 7.31×10-4 A after irradiation to a fluence of 1×1012 ions/cm2. Base current increases whereas collector current decreases after irradiation with a fluence of 1×1012 ions/cm2. The magnitude of decrease in collector current is approximately same as that of the increase in base current, showing the leakage of the collector current due to irradiation. The output collector gain of the unirradiated transistor is 20.5 after irradiation to a fluence of 1×1012 ions/cm2 it has reduced to 0.81. The capacitance measurements for base-emitter junction show that for the unirradiated and irradiated samples, linearity of the curves indicate uniformity of shallow doping concentration. The built in potential (Vbi) for unirradiated device is 2.69V and after irradiation it is 2.52V. The device is also studied for activation energy, trap concentration and capture cross-section of deep levels are studied using deep-level transient spectroscopy (DLTS) technique. Majority carrier trap level is observed with energy Ev+0.784eV.

Effects of pulsed laser annealing on deep level defects in electrochemically-deposited and furnace annealed CuInSe2 thin films

CuInSe2 (CISe) is a prototype material for the I–III–VI chalcopyrites such as Cu(In,Ga)(S,Se)2 used as absorber layers in thin film photovoltaic cells. Carefully-controlled pulsed-laser annealing (PLA) is a unique annealing process that has been demonstrated to improve the device performance of chalcopyrite solar cells. Here, we investigate the changes in defect populations after PLA of electrochemically-deposited CISe thin films previously furnace annealed in selenium vapor. The films were irradiated in the sub-melting regime at fluences inducing temperatures up to 840±100K. Deep-level transient spectroscopy on Schottky diodes reveals that the activation energy of the dominant majority carrier trap changes non-monotonically from 215±10meV for the reference sample, to 330±10meV for samples irradiated at 20 and 30mJ/cm2, and then back to 215±10meV for samples irradiated at 40mJ/cm2. A hypothesis involving competing processes of diffusion of Cu and laser-induced generation of In vacancies may explain this behavior.

DLTS and MCTS analysis of the influence of growth pressure on trap generation in MOCVD GaN

We demonstrate with DLTS and MCTS how changing growth pressure during MOCVD growth of GaN affects the majority and minority carrier trap signatures. Results indicate which specific traps are most strongly connected with the increased carbon concentration that lower growth pressure has led to. Carbon concentration is also verified with SIMS measurements. DLTS and MCTS measurements, related to carrier thermalization from traps, made up to a temperature of 450K have found four majority carrier and two minority carrier traps. Using a lower growth pressures, at which greater incorporation of carbon is possible, has lead to larger concentrations of most of the traps; just as others have observed. However, the trap at EC−0.48eV is the least affected by the growth pressure. We relate all the traps found from DLTS and MCTS to those identified by others and mention the constituent atoms that the research community identifies with these traps.

Characterization of Metamorphic GaAsP/Si Materials and Devices for Photovoltaic Applications

GaAs <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> anion-sublattice compositionally graded buffers and device structures were grown directly on Si(100) substrates by way of a high-quality GaP integration layer, yielding GaAsP target layers having band gaps of photovoltaic interest (1.65-1.8 eV), free of antiphase domains/borders, stacking faults, and microtwins. GaAs <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> growths on both Si and GaP substrates were compared via high-resolution X-ray diffractometry of the metamorphic buffers and deep-level transient spectroscopy (DLTS) of p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -n diodes that are lattice matched to the final buffer layer. Structural analysis indicates highly efficient epitaxial relaxation throughout the entire growth structure for both types of samples and suggests no significant difference in physical behavior between the two types of samples. DLTS measurements performed on GaAsP diodes fabricated on both Si and GaP substrates reveal the existence of identical sets of traps residing in the n-type GaAsP layers in both types of samples: a single majority carrier (electron) trap, which is located at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EC</i> - 0.18 eV, and a single minority carrier (hole) trap, which is located at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EV</i> + 0.71 eV. Prototype 1.75-eV GaAsP solar cell test devices grown on GaAs <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> /Si buffers show good preliminary performance characteristics and offer great promise for future high-efficiency III-V photovoltaics integrated with Si substrates and devices.

Trapping of majority carriers in SiO2/4H-SiC structures

We compared SiO2/SiC interface characteristics for three different oxidation processes (dry-oxygen, water-containing oxygen and water-containing nitrogen atmospheres). Metal-oxide-semiconductor (MOS) structures were fabricated on 8° off-axis 4H-SiC(0001) n- and p-type epitaxial wafers. Electrical characteristics were obtained by I–V measurements, high-frequency capacitance–voltage (C–V) and ac conductance (G–V and G–ω) methods. The samples were also characterized by x-ray photoelectron spectroscopy. Results evidence a remarkable difference between n- and p-type doped samples. The p-type samples showed effective oxide charge density up to three orders of magnitude higher than n-type. This fact was explained by the capturing of majority carriers in near interface oxide traps.

Deep defects in GaN/AlGaN/SiC heterostructures

Deep level transient spectroscopy (DLTS) measurements were carried out on GaN/AlGaN/SiC heterostructures prepared by low-pressure metalorganic vapor phase epitaxy. Si-doped n-GaN layers were grown using an n-AlGaN nucleation layer (8% and 30% of aluminum) on two kinds of p-type 4H-SiC substrates. The DLTS spectra of on-axis (0001) grown samples exhibit a dominant peak of a majority carrier trap with apparent activation energy close to 0.80 eV and capture cross section of about 5×10−14 cm2 regardless of the AlGaN composition. The energy of this deep level decreases with increasing electrical field due to Poole–Frenkel effect. Carrier capture kinetics indicates interacting point defects arranged along a line, probably a threading dislocation. Two additional traps (0.52 and 0.83 eV) were found in on-axis samples with 8% AlGaN composition. For 30% Al content, only a 0.83 eV level was detected. Majority carrier trap with activation energy of 0.66 eV was observed in the off-axis grown samples. This level is probably related to an interface defect or to a defect lying near the heterojunction interface.

Effects of internal fields on deep-level emission in InGaN/GaN quantum-well light-emitting diodes

We report on the important role played by internal quantum well (QW) fields in the anomalous inversion of capacitance transients in InGaN/GaN multi-QW light-emitting diodes (LEDs). This effect was observed by deep-level transient spectroscopy (DLTS) characterization. Deep-level C (EC–ET=0.25eV), a majority carrier trap related to isolated point defects, gives rise to a negative transient when the bias stimulates it only in the bulk region and to a positive transient when the filling pulse is such that the QW region is probed. We explain this behavior by a model based on the confining effects of QW internal fields on the charge emitted by deep levels.