Activation Capture Cross Section Research Articles

Observation of temperature-dependent capture cross section for main deep-levels in β-Ga2O3

Direct observation of the capture cross section is challenging due to the need for extremely short filling pulses in the two-gate Deep-Level Transient Spectroscopy (DLTS). Simple estimation of the cross section can be done from DLTS and admittance spectroscopy data but it is not feasible to distinguish temperature dependence of pre-exponential and exponential parts of the emission rate equation with sufficient precision conducting a single experiment. This paper presents experimental data of deep levels in β-Ga2O3 that has been gathered by our group since 2017. Based on the gathered data, we propose a derivation of apparent activation energy (Eam) and capture cross section (σnm) assuming the temperature dependent capture via the multiphonon emission model, which resulted in a strong correlation between Eam and σnm according to the Meyer–Neldel rule, which allowed us to estimate low- and high-temperature capture coefficients C0 and C1 as well as capture barrier Eb. It also has been shown that without considering the temperature dependence of capture cross section, the experimental values of σn are overestimated by 1–3 orders of magnitude. A careful consideration of the data also allows to be more certain identifying deep levels by their “fingerprints” (Ea and σn) considering two additional parameters (EMN and σ00) and to verify the density functional theory computation of deep-level recombination properties.

Investigation of Current Collapse Mechanism on AlGaN/GaN Power Diodes

In this paper, a methodology is proposed for studying the current collapse effects of Gallium Nitride (GaN) power diodes and the consequences on the dynamic on-resistance (RON). Indeed, the growing interest of GaN based, high frequency power conversion requires an accurate characterization and a deep understanding of the device’s behaviour before any development of power converters. This study can ultimately be used to model observed trap effects and, thus, improve the equivalent electrical model. Using an in-house circuit and a specific experimental setup, a current-collapse phenomenon inherent to gallium nitride semiconductor is studied on planar 650 V—6 A GaN diodes by applying high voltage stresses over a wide range of temperatures. With this method, useful data on activation energy and capture cross section of electrical defects linked to dynamic RON are extracted. Finally, the origins of such defects are discussed and attributed to carbon-related defects.

Influence of the type of interlayer on current transport mechanisms and defects in n-ZnO/ZnCdO/p-Si and n-ZnCdO/ZnO/p-Si heterojunctions grown by molecular beam epitaxy

A pair of heterojunctions with different type of interlayer: n-ZnO/ZnCdO and n-ZnCdO/ZnO were grown by molecular beam epitaxy on p-Si substrate and investigated in the present work. At first, their electrical properties and parameters were discussed following current-voltage (I-V) characteristics measured over a wide range of temperatures from 40 K to 300 K. The analysis of I-V plots in log-log scale pointed out the presence of different carrier transport mechanisms: tunneling, multi-tunneling capture-emission and space-charge limited currents. Next, the capacitance-voltage characteristics were studied to determine the dopant concentration of the investigated junctions, along with the net doping profiles and their temperature dependence in the range of 40 K to 300 K. Finally, a deep level transient spectroscopy method was applied to characterise defects in the studied junctions. Donor-like traps were identified and their parameters, such as activation energy and capture cross section, were calculated. Furthermore, the influence of cadmium ions in ZnCdO interlayer of n-ZnO/ZnCdO/p-Si diode on the energy position of trap levels was noticed. Moreover, it was demonstrated that the interlayer type affects junction parameters, especially its built-in potential, as well as it modifies the current transport mechanisms in the intermediate range of voltage.

Diode characteristics of ZnO/ZnMgO nanowire p-n junctions grown on Si by molecular beam epitaxy

In this paper we focus on fundamental studies of ZnO/ZnMgO nanowire p-n junctions grown by MBE on Si substrate for UV light emitting sources. A lot of attention is paid on investigation of defects responsible for optical emission form the nanowires. Electro-optical properties of the diodes as well as deep level traps have been studied by means of photoluminescence (PL) and deep level transient spectroscopy (DLTS). To perform electrical measurements of the aforementioned nanowire structures p-n junctions of n-ZnMgO/p-Si were fabricated and their quality has been verified in measurements of I-V and C-V characteristics. PL experiments were conducted in the near- UV and visible spectral range. They provided information on the excitonic transitions associated with quantum wells (QWs). Moreover, a broad emission peak located at ~ 2.3 eV (~540 nm) assigned to deep-level-emission (DLE) was also observed. The origin of the DLE band in the PL spectra has been further analyzed by means of electrical methods. The C-V results proved that the depletion region of the studied diodes is located on the n-type side of the p-n junction. The DLTS measurements revealed the presence of electron traps related with ZnO. The parameters of the traps, such as activation energies and capture cross sections, were determined and the source of their origin has been discussed. The results obtained within this work helped us to understand the impact of defects/QWs on electrical and optical properties of the studied nanowire n-ZnMgO/p-Si diodes.

Effect of carrier drift-diffusion transport process on thermal quenching of photoluminescence in GaN

Thermal quenching of the defect-related photoluminescence (PL) has been widely used to determine the fundamental properties of point defects in GaN such as the activation energy (E t ) and capture cross section. However, in the present work, we have shown using drift-diffusion modeling and experimental analysis that the thermal quenching of defect-related PL from GaN does not only depend of the defect parameters but also is strongly governed by the carrier drift and diffusion in the depletion region. In particular, we have found that these processes significantly influence the slope of PL thermal quenching and temperature T 0 at which the quenching begins. As a result, E t obtained from the Arrhenius plot of the defect-related PL intensity in GaN provides the correct values of the defect activation energy only in the case of low surface state density ( cm−2eV−1) corresponding to the weak surface band bending. However, in the case of high D 0 giving rise to the significant surface band bending, the E t value should be cautiously interpreted because it may not correspond entirely to the real defect activation energy due to the drift-diffusion process. Finally, we have shown that our finding can explain in a coherent manner various anomalous behaviors of PL thermal quenching reported in the literature, such as tunable, abrupt or sample dependent thermal quenching. We believe that our findings can be very interesting for nitride growth technology community and optoelectronic device applications.

Electroluminescence analysis of VOC degradation of individual subcell in GaInP/GaAs/Ge space solar cells irradiated by 1.0 MeV electrons

The open-circuit voltage (VOC) degradation for individual subcell in 1.0 MeV electrons-irradiated GaInP/GaAs/Ge solar cells has been analyzed using electroluminescence (EL) measurements. By using the relationship between VOC degradation and electron fluence, the capture cross section of the defects induced by electron irradiation in individual subcells were determined. Furthermore, by comparing the thermal activation energy and capture cross section, a defect located at Ev+0.55 ​eV styled H2 hole trap is nonradiative recombination centre in GaInP subcell, a defect located at EC-0.96 eV styled E5 electron trap is nonradiative recombination centre in GaAs subcell, and a defect located at EC-0.38 eV styled E-center electron trap is nonradiative recombination centre in Ge subcell.

Peak shape analysis of deep level transient spectra: An alternative to the Arrhenius plot

Abstract

Deep levels in the MBE ZnO:As/n-GaN diodes – Photoluminescence, electrical properties and deep level transient spectroscopy

In this paper the current understanding of defects in acceptor doped ZnO is briefly reviewed. The results of investigations of ZnO:As/n-GaN heterojunctions which have been successfully fabricated by plasma assisted molecular beam epitaxy method are presented. The electrical properties of the junctions, as well as deep levels, have been studied by means of current-voltage (I-V), capacitance-voltage (C-V) characteristics and deep level transient spectroscopy (DLTS). Electrical measurements were supplemented by photoluminescence- (PL) along with secondary ion mass spectrometry (SIMS) and X-ray photoemission spectroscopy (XPS) investigations. The I-V measurements allowed for detailed analysis of current mechanisms, through which the presence of trap states in the investigated junction was confirmed. The C-V results proved that the depletion region of the diode is located within the ZnO:As layer. The DLTS measurements revealed the presence of three hole trap related signals. The activation energies and capture cross sections of these traps were determined and their possible origin has been ascribed. Obtained results allowed for better identification of defects found in the case of the analyzed heterostructure, as well as the studies of its electronic properties.

Kinetics of Buffer-Related R<sub>ON</sub>-Increase in GaN-on-Silicon MIS-HEMTs

This letter reports an extensive analysis of the charge capture transients induced by OFF-state bias in double heterostructure AlGaN/GaN MIS- high electron mobility transistor grown on silicon substrate. The exposure to OFF-state bias induces a significant increase in the ON-resistance (R on ) of the devices. Thanks to time-resolved on-the-fly analysis of the trapping kinetics, we demonstrate the following relevant results: 1) R on -increase is temperature- and field-dependent, hence can significantly limit the dynamic performance of the devices at relatively high-voltage and high temperature (100 °C-140 °C) operative conditions; 2) the comparison between OFF-state and back-gating stress indicates that the major contribution to the R on -increase is due to the trapping of electrons in the buffer, and not at the surface; 3) the observed exponential kinetics suggests the involvement of point-defects, featuring thermally activated capture cross section; and 4) trapping-rate is correlated with buffer vertical leakage-current and is almost independent to gate-drain length.

Determination of energy and spatial distribution of oxide border traps in In0.53Ga0.47As MOS capacitors from capacitance–voltage characteristics measured at various temperatures

In this work, we have systematically studied the frequency dispersion of the capacitance–voltage (C–V) characteristics of In0.53Ga0.47As metal–oxide-semiconductor (MOS) capacitors in accumulation region at various temperatures based on a distributed border traps model. An empirical method to evaluate the frequency and temperature dependent response of the border traps distributed along the depth from the interface into the oxide is established. While the frequency dependent response results from the dependence of the time constant of the border traps on their depths, the temperature dependent response is ascribed to the thermal activated capture cross-section of the border traps due to the phonon-related inelastic capturing process. Consequently, it is revealed that the frequency dispersion behaviors of the accumulation capacitance at different temperatures actually reflect the spatial distribution of the border traps. On this basis, we propose a methodology to extract the border trap distribution in energy and space with emphasis on analyzing the C–V characteristics measured from low to high temperatures in sequence.

Deep traps in n-type GaN epilayers grown by plasma assisted molecular beam epitaxy

In this study, we present the results of investigations on Schottky Au-GaN diodes by means of conventional DLTS and Laplace DLTS methods within the temperature range of 77 K–350 K. Undoped GaN layers were grown using the plasma-assisted molecular beam epitaxy technique on commercial GaN/sapphire templates. The quality of the epilayers was studied by micro-Raman spectroscopy (μ-RS) which proved the hexagonal phase and good crystallinity of GaN epilayers as well as a slight strain. The photoluminescence spectrum confirmed a high crystal quality by intense excitonic emission but it also exhibited a blue emission band of low intensity. DLTS signal spectra revealed the presence of four majority traps: two high-temperature and two low-temperature peaks. Using the Laplace DLTS method and Arrhenius plots, the apparent activation energy and capture cross sections were obtained. For two high-temperature majority traps, they were equal to E1 = 0.65 eV, σ1 = 8.2 × 10−16 cm2 and E2 = 0.58 eV, σ2 = 2.6 × 10−15 cm2 whereas for the two low-temperature majority traps they were equal to E3 = 0.18 eV, σ3 = 9.7 × 10−18 cm2 and E4 = 0.13 eV, σ4 = 9.2 × 10−18 cm2. The possible origin of the traps is discussed and the results are compared with data reported elsewhere.

Deep levels in GaN studied by deep level transient spectroscopy and Laplace transform deep-level spectroscopy

In this study we present the results of investigations on Schottky Au-GaN diodes by means of conventional DLTS and Laplace DLTS methods within the temperature range of 77–350 K. Si-doped GaN layers were grown by Molecular Beam Epitaxy technique (MBE) on sapphire substrates. DLTS signal spectra revealed the presence of four majority traps: two hightemperature and two low-temperature peaks. Using LDLTS method and Arrhenius plots the activation energy and capture cross sections were obtained. For two high-temperature majority traps they are equal to E1 = 0.65 eV, σ1 = 8.2 × 10−16cm2 and E2 = 0.58 eV, σ2 = 2.6 × 10−15 cm2 whereas for the two low-temperature majority traps E3 = 0.18 eV, σ3 = 9.72 × 10−18 cm2 and E4 = 0.13 eV, σ4 = 9.17 × 10−18 cm2. It was also found that the traps are related to point defects. Possible origin of the traps was discussed and the results were compared with the data found elsewhere [1–5].

Assessing the role of iron‐acceptor pairs in solar grade multicrystalline silicon wafers from the metallurgical route

AbstractThe recombination parameters of iron‐boron (FeB), iron‐aluminium (FeAl) and iron‐gallium (FeGa) pairs in Fe implanted FZ monocrystalline silicon wafers and Fe contaminated multicrystalline silicon (mc‐Si) wafers of solar grade feedstock from the metallurgical route have been studied by combining the Deep Level Transient Spectroscopy (DLTS) and Microwave Photoconductive Decay (µ‐PCD) techniques. Energy levels associated with FeB, FeAl and FeGa pairs were detected in the monocrystalline samples. The activation energy and capture cross section of these levels were determined. FeGa gave the strongest recombination effect, reducing the minority carrier lifetime of the sample from about 39 µs to 0.7 µs at a concentration of 4x1013 cm‐3. No electrically active iron‐acceptor pairs could be detected in the mc‐Si wafer. However, it was demonstrated that micrometer‐sized clusters, most likely composed of metallic oxides, collect iron from the bulk. This iron collection may reduce the available amount of iron for creating electrically active iron‐acceptor pairs below the detection limit of DLTS. The contamination did, however, degrade the lifetime from 40 µs to less than 1 µs in the wafer. This is likely a result of at least three overlapping energy levels believed to be related to iron (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Identification of traps in an epitaxied AlGaAs/GaAs/AlGaAs quantum well structure

An epitaxied AlGaAs/GaAs/AlGaAs heterostructure is studied by using the low frequency noise technique over a wide range of temperature from 300 K down to 4 K as a function of bias. Emphasis is placed on the generation—recombination noise because it is present on a wide range of temperature and frequency. Thermal activation energies and capture cross sections of traps responsible for this kind of noise are extracted from an arrhenius plot. Six kinds of traps have been identified and their electrical nature has been suggested.

Trap characterization in AlGaN/GaN HEMT by analyzing frequency dispersion in capacitance and conductance

AbstractAn analysis of frequency dispersion in capacitance and conductance of gate‐source contact of AlGaN/GaN HEMT was performed. Capacitance and conductance were measured at temperatures varying from 83 K to 370 K with bias voltage maintained at 0 V. In order to characterize trap states the conductance method was used considering series resistance. Hence, the parallel conductance Gp and capacitance Cp were calculated, and consequently interface trap density Dit and time constant t are deduced. The analysis is performed assuming a continuum of levels yielding to a trap density of approximately 10+12 cm−2eV−1 and a time constant varying between 1 µs and 3 ms. Activation energies and capture cross sections of three trap levels were deduced and their values were respectively (ΔEa1 = 0.201 eV, σn1 = 4.992 × 10−18 cm2), (ΔEa2 = 0.053 eV, σn2 = 2.585 × 10−21 cm2), (ΔEa3 = 0.121 eV, σn3 = 1.256 × 10−20 cm2). An electrical model was established with two levels of traps at AlGaN/GaN interface and one level located in barrier AlGaN surface. Copyright © 2010 John Wiley & Sons, Ltd.

Morphological, structural and electrical investigations on non-polar a-plane ZnO epilayers

We report on the growth of non-polar a-plane ZnO by CVD on r-plane-sapphire-wafers, a-plane GaN-templates and a-plane ZnO single-crystal substrates. Only the homoepitaxial growth approach leads to a Frank–van-der–Merwe growth mode, as shown by atomic force microscopy. The X-ray-diffraction spectra of the homoepitaxial thin films mirror the excellent crystalline quality of the ZnO substrate. The morphological and the structural quality of the homoepitaxial films is comparable to the best results for the growth on c-plane ZnO-substrates. The impurity incorporation, especially of group III elements, seems to be reduced when growing on the non-polar a-plane surface compared to the c-plane films as demonstrated by secondary ion mass spectrometry (SIMS). Optical properties have been investigated using low temperature photoluminescence measurements. We employed capacitance–voltage measurements ( C– V) to measure the background carrier density and its profile from substrate/film interface throughout the film to the surface. In thermal admittance spectroscopy (TAS) specific traps could be distinguished, and their thermal activation energies and capture cross sections could be determined.

Characterization of 4H-SiC Junction Barrier Schottky Diodes by Admittance vs Temperature Analyses

Schottky barrier diodes and junction barrier Schottky diodes are investigated by thermal admittance spectroscopy, and by Capacitance-Voltage measurements. Samples are protected with surrounding junction termination extension and p+ ring. Temperature dependence of the doping level is first calculated. Then admittance spectra allow detecting defects and extracting their activation energies and capture cross sections. Results seem to indicate the presence of interfacial defects and defects due to the implantation process.

I-V and DLTS study of generation and annihilation of deep-level defects in an oxygen-ion irradiated bipolar junction transistor

A commercial bipolar junction transistor (2N 2219A, npn) irradiated with 84 MeV O6+-ions with fluence of the order of 1013 ions cm−2 is studied for radiation-induced gain degradation and deep-level defects or recombination centers. I-V measurements are made to study the gain degradation as a function of ion fluence. Properties such as activation energy, trap concentration and capture cross section of deep levels are studied by deep-level transient spectroscopy. Minority carrier trap energy levels with energies ranging from E C −0.17 eV to E C −0.55 eV are observed in the base–collector junction of the transistor. Majority carrier defect levels are also observed with energies ranging from E V +0.26 eV to E V +0.44 eV. The irradiated device is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 250 °C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for an increase in base current through Shockley-Read-Hall or multi-phonon recombination and consequent transistor gain degradation.

Analysis of generation and annihilation of deep level defects in a silicon-irradiated bipolar junction transistor

A commercial bipolar junction transistor (2 N 2219 A, npn), irradiated with 120 MeV Si9+ ions with a fluence of the order of 1012 ions cm−2, is studied for radiation-induced gain degradation and deep level defects. I–V measurements are made to study the gain degradation as a function of ion fluence. Properties such as activation energy, trap concentration and capture cross section of deep levels are studied by deep level transient spectroscopy (DLTS). Minority carrier trap energy levels with energies ranging from EC − 0.160 eV to EC − 0.581 eV are observed in the base-collector junction of the transistor. Majority carrier trap levels are also observed with energies ranging from EV + 0.182 eV to EV + 0.401 eV. The identification of the defect type is made on the basis of its finger prints such as activation energy, annealing temperature and capture cross section by comparing with those reported in the literature. New energy levels for the defects A-center, di-vacancy and Si-interstitial are also observed. The irradiated transistor is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 250 °C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for transistor gain degradation.

Extremely small hole capture cross sections in HfO2∕HfxSiyOz∕p-Si structures

Defects in Al∕HfO2∕HfxSiyOz∕p-Si capacitors have been characterized using thermally stimulated current at temperatures between 30 and 300K. The hole activation energy and capture cross section were extracted from the results. The authors observed shallow traps that move with changing the discharging voltage, giving rise to activation energies in the range 0.03–0.14eV. Postmetallization anneal passivated these traps and a deeper trap appears with a significantly lower shift with the discharging voltage. Very small apparent capture cross sections (capture cross section times tunneling probability) have been extracted (10−26–10−18cm2). Simulations agree very well with experimental data.