Search

Hafnium oxide (HfO2) has been explored as high-κ gate dielectrics in scaled CMOS devices, artificial synapses to be used in neuromorphic computing to achieve brain-like functionalities, a storage layer in memory devices, a piezoelectric energy harvester, and a photodetector. In this article, the origin of a native defect present in the HfO2 thin films on silicon is experimentally probed using deep level transient spectroscopy (DLTS) technique. It was realized that defects (predominantly oxygen vacancies) in HfO2 segregate near the Si/HfO2 interface. The interfacial and bulk HfO2 trap charges are communicating through the tunneling/ hopping, and, finally, they are emitted to the respective bands of silicon depending on the silicon used. We have observed four prominent defect states, and we believe that all these belong to oxygen vacancies in different charge states. The activation energies of trap states are in the range of 1.22–2.02 eV from the HfO2 conduction band edge, and they fall in front of the Si bandgap in the band alignment of the Al/HfO2/Si gate stack. The capture cross sections of these traps are measured with insufficient filling DLTS and found to be of the order of 10−19 cm2. The results provide valuable insights into realizing the behavior of oxygen vacancy-related deep defects in HfO2 and guide their possible impact on the device performance. [ABSTRACT FROM AUTHOR]

The relationship between the electrical properties and the carrier trap properties of the SiO2/GaN metal–oxide–semiconductor (MOS) capacitors was investigated using electrical measurements and deep level transient spectroscopy (DLTS). The capacitance–voltage (C–V) measurement showed that the frequency dispersion of the C–V curves became smaller after an 800 °C annealing in O2 ambient. DLTS revealed that before the annealing, the interface trap states, in a broad energy range above the midgap of GaN, were detected with the higher interface state density at around 0.3 and 0.9 eV below the conduction band minimum (EC) of GaN. Moreover, the oxide trap states were formed at around 0.1 eV below the EC of GaN, plausibly indicating a slow electron trap with a tunneling process. Although both trap states affect the electrical reliability and insulating property of the SiO2/GaN MOS capacitors, they were found to drastically decrease after the annealing, leading to the improvement of the electrical properties. [ABSTRACT FROM AUTHOR]

Electrically detected magnetic resonance (EDMR) is arguably the most sensitive method available to study electrically active point defects in semiconductor devices. Most EDMR studies have utilized spin-dependent recombination current and, thus, require p–n junctions or a photoconductive structure. Some time ago, Chen and Lang proposed and demonstrated EDMR via spin-dependent deep level transient spectroscopy in metal–oxide–semiconductor capacitors. We report on a similar and significantly simpler technique: spin-dependent transient spectroscopy (SDTS). We show that the sensitivity of this technique is independent of the resonance field and frequency. Through capacitance–voltage analysis, combined with our SDTS results, this technique can (crudely) provide information about the density of states of defects with a broad distribution of energy levels. In addition, we show that SDTS can be readily adapted to near-zero-field magnetoresistance effect measurements. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) are disruptive materials for a vast class of optoelectronic devices. The presence of electronic trap states has been a tough challenge in terms of characterization and thus mitigation. Many attempts based on electronic spectroscopies have been tested, but due to the mixed electronic-ionic nature of MHP conductivity, many experimental results retain a large ambiguity in resolving electronic and ionic charge contributions. Here we adapt a method, previously used in highly resistive inorganic semiconductors, called photoinduced current transient spectroscopy (PICTS) on lead bromide 2D-like ((PEA)2PbBr4) and standard 3D (MAPbBr3) MHP single crystals. We present two conceptually different outcomes of the PICTS measurements, distinguishing the different electronic and ionic contributions to the photocurrents based on the different ion drift of the two materials. Our experiments unveil deep level trap states on the 2D, ion-frozen (PEA)2PbBr4 and set new boundaries for the applicability of PICTS on 3D MHPs.

The ultra-wide bandgap of gallium oxide provides a rich plethora of electrically active defects. Understanding and controlling such defects is of crucial importance in mature device processing. Deep-level transient spectroscopy is one of the most sensitive techniques for measuring electrically active defects in semiconductors and, hence, a key technique for progress toward gallium oxide-based components, including Schottky barrier diodes and field-effect transistors. However, deep-level transient spectroscopy does not provide chemical or configurational information about the defect signature and must, therefore, be combined with other experimental techniques or theoretical modeling to gain a deeper understanding of the defect physics. Here, we discuss the current status regarding the identification of electrically active defects in beta-phase gallium oxide, as observed by deep-level transient spectroscopy and supported by first-principles defect calculations based on the density functional theory. We also discuss the coordinated use of the experiment and theory as a powerful approach for studying electrically active defects and highlight some of the interesting but challenging issues related to the characterization and control of defects in this fascinating material. [ABSTRACT FROM AUTHOR]

The dependence of the electrical characteristics on the fast neutron fluence of an epitaxial 4H–SiC Schottky barrier diode (SBD) was investigated. The 30 MeV cyclotron was used for fast neutron irradiation. The neutron fluences evaluated through Monte Carlo simulation were in the 2.7 × 1011 to 1.45 × 1013 neutrons/cm2 range. Current–voltage and capacitance–voltage measurements were performed to characterize the samples by extracting the parameters of the irradiated SBDs. Neutron-induced defects in the epitaxial layer were identified and quantified using a deep-level transient spectroscopy measurement system developed at the Korea Atomic Energy Research Institute. As the neutron fluence increased from 2.7 × 1011 to 1.45 × 1013 neutrons/cm2, the concentration of the Z1/2 defects increased by approximately 20 times. The maximum defect concentration was estimated as 1.5 × 1014 cm−3 at a neutron fluence of 1.45 × 1013 neutrons/cm2.

In this study, we provide fundamental understanding on defect properties of the Sb2(S,Se)3 absorber film and the impact on transmission of photo-excited carriers in N–i–P architecture solar cells by both deep level transient spectroscopy (DLTS) and optical deep level transient spectroscopy (ODLTS) characterizations. Through conductance–voltage and temperature-dependent current–voltage characterization under a dark condition, we find that the Sb2(S,Se)3 solar cell demonstrates good rectification and high temperature tolerance. The DLTS results indicates that there are two types of deep level hole traps H1 and H2 with active energy of 0.52 eV and 0.76 eV in the Sb2(S,Se)3 film, and this defect property is further verified by ODLTS. The two traps hinder the transmission of minority carrier (hole) and pinning the Fermi level, which plays a negative role in the improvement of open-circuit voltage for Sb2(S,Se)3 solar cells. This research suggests a critical direction toward the efficiency improvement of Sb2(S,Se)3 solar cells. [ABSTRACT FROM AUTHOR]

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 (E a m) and capture cross section (σ n m) assuming the temperature dependent capture via the multiphonon emission model, which resulted in a strong correlation between E a m and σ n m according to the Meyer–Neldel rule, which allowed us to estimate low- and high-temperature capture coefficients C 0 and C 1 as well as capture barrier E b. It also has been shown that without considering the temperature dependence of capture cross section, the experimental values of σ n 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" (E a and σ n) considering two additional parameters (E M N and σ 00) and to verify the density functional theory computation of deep-level recombination properties. [ABSTRACT FROM AUTHOR]

This work reports on a comprehensive examination of the electrical and thermal properties of vertical Schottky diodes fabricated on (201)- and (001)-oriented samples of β-Ga2O3. The temperature-dependent current--voltage (I-V) and capacitance--voltage (C-V) data were gathered and analyzed down to 60 K. Deep level transient spectroscopy (DLTS) was used to study bulk and interface defects in the two materials from approx. 325 K down to 60 K. In the bulk (201) material, an electron trap was observed at EC-0.46 eV, with a capture cross section of 1.6 x 10-14 cm² and a lambda-corrected maximum trap density of 9.08 x 1015 cm-3. These results and others indicate that the electron trap is a strong candidate for the well-known E1 defect in β-Ga2O3 based on recent investigations. Additionally, in the (201) material, the smooth modulation typical of interface states is evident at temperatures below 275 K. The (001) samples manifested what is likely the E2* electron trap at EC-0.68 eV, with a capture cross section of 1.64 x 10-15 cm² and a lambda-corrected maximum trap density of 8.85 x 1015 cm-3. The presence of the E2* defect, in particular, is a contrast to the findings of recent DLTS investigations on β-Ga2O3, which report that E2* emerged only after low-energy proton irradiation. These results help to further map out the defect signatures found in β-Ga2O3 materials, which are of vital importance in the design and fabrication of future β-Ga2O3 devices. [ABSTRACT FROM AUTHOR]

In this work, we described the variations in the defect energy levels of four different ZnO morphologies, namely nanoribbons, nanorods, nanoparticles, and nanoshuttles. All the ZnO morphologies were grown on a seeded 4% Boron-doped p-type silicon (p-Si) wafer by using two different synthesis techniques, which are chemical bath deposition and microwave-assisted methods. The defect energy levels were analyzed by using the Deep-Level Transient Spectroscopy (DLTS) characterization method. The DLTS measurements were performed in the 123 K to 423 K temperature range. From the DLTS spectra, we found the presence of different trap-related defects in the synthesized ZnO nanostructures. We labeled all the traps related to the four different ZnO nanostructures as P1, P2, P3, P4, and P5. We discussed the presence of defects by measuring the activation energy (Ea) and capture cross-section (α). The lowest number of defect energy levels was exhibited by the ZnO nanorods at 0.27 eV, 0.18 eV, and 0.75 eV. Both the ZnO nanoribbons and nanoparticles show four traps, which have energies of 0.31 eV, 0.23 eV, 0.87 eV, and 0.44 eV and 0.27 eV, 0.22 eV, 0.88 eV, and 0.51 eV, respectively. From the DLTS spectrum of the nanoshuttles, we observe five traps with different activation energies of 0.13 eV, 0.28 eV, 0.25 eV, 0.94 eV, and 0.50 eV. The DLTS analysis revealed that the origin of the nanostructure defect energy levels can be attributed to Zinc vacancies (Vzn), Oxygen vacancies (Vo), Zinc interstitials (Zni), Oxygen interstitials (Oi), and Zinc antisites (Zno). Based on our analysis, the ZnO nanorods showed the lowest number of defect energy levels compared to the other ZnO morphologies.

In this work, we have performed a detailed study of the defects created in the bulk of 4H-SiC after thermal oxidation and post oxidation annealing using deep level transient spectroscopy and minority carrier transient spectroscopy (MCTS). The study reveals the formation of several shallow and deep level majority carrier traps in the bandgap. The ON1 (E C − 0.85 eV), ON2a (E C − 1.05 eV), and ON2b (E c − 1.17 eV) levels are the most dominant and are observed across all the samples (E C denotes the conduction band edge). Three shallow levels Ti(k) (E C − 0.17 eV), E 0.23 (E C − 0.23 eV), and C 1 / 2 (E C − 0.36 / 0.39 eV) are observed in the samples. For most of the majority carrier defects, the highest concentration is observed after an NO anneal at 1300 ° C. This behavior is sustained in the depth profile measurements where the defect concentration after the NO anneal at 1300 ° C is significantly higher than for the rest of the samples. The origin of most of the majority carrier defects has been attributed to C interstitial injection from the interface during thermal oxidation and annealing. MCTS measurements reveal two prominent minority carrier traps, labeled O 0.17 (E V + 0.17 eV) and B (E V + 0.28 eV), where the concentration of O 0.17 is independent of annealing parameters while the concentration of the B level increases after the NO anneal (E V denotes the valence band edge). Furthermore, the depth profiles of the defects are used to evaluate their diffusion parameters by solving the diffusion equation to fit the experimental profiles. The defect concentrations decay exponentially with depth, which evidences that the defects were created at or near the SiO 2 –SiC interface and migrate toward the bulk during oxidation and post-oxidation annealing. [ABSTRACT FROM AUTHOR]

Deep Level Transient Spectroscopy (DLTS) is a technique used to identify and characterize deep defects in materials. New kind of setups using impedance analysers are developed over capacitance bridges. The impedance analyser from Zurich Instruments MFIA has gained significant interest due to its versality, availability and relatively low cost of the device. Consequently, the need for a software utilizing this device for the DLTS measurements has emerged. In this work, we present LabVIEW based software for DLTS using the MFIA impedance analyser. The most significant characteristics of the application include great functionality, effortless customization, and user-friendly interface.

We have developed a micro-controller based Deep Level Transient Spectroscopy (DLTS) system to identify the deep-level defects in semiconductors. It consists of Arduino-Due, a capacitance meter, and interface circuits. In addition, we have also developed the algorithms needed for the entire signal processing. It is not limited to Arduino-Due but can be implemented using other micro-controllers also. We have used Arduino-Due to generate the filling pulse and monitor the capacitance, temperature, data acquisition, timing control, and signal processing. The sequence of generating the filling pulse, reading the data, and signal processing is controlled digitally rather than by analog sampling circuits and timers. The minimum pulse width generated using Arduino-Due is 50 ns; the pulse width generation depends on various hardware and software parameters and their integration. The resolution in reading the data is 0.8 mV/unit. The time delays in reading the data are appropriately taken care of in the system. The whole experiment can be completed in a single temperature cycle within 2–3 h. The system is simple, inexpensive, in an easy-to-use platform, and less time-consuming; minimizes possible errors; and improves accuracy. The measurements using the "micro-controller based DLTS system" are verified by fabricating (Au) gold-doped silicon (Si) p–n junction samples (Au is a well-understood defect in Si). Using the Arduino-Due based DLTS system, we calculated the energy, the capture cross section, and the concentration of trap levels. The results are in good agreement with the literature, indicating the versatility of the system. [ABSTRACT FROM AUTHOR]

Chalcogenide semiconductors have emerged as promising candidates for next-generation optoelectronics, mainly benefiting from their cost-effective processability, chemical versatility, and excellent stability. However, the device performance is limited by the complex defect characteristics, necessitating a detailed understanding of the defect density, types, and distribution. This study employs optical injection deep level transient spectroscopy to characterize the trap features of antimony bismuth sulfide-based heterojunctions. Photoexcitation offers the possibility to determine the spatial distribution of traps. It reveals distinct distributions of hole and electron traps. Short-wavelength light (570 nm) detects hole traps near the hole transport layer, while long-wavelength light (830 nm) identifies electron traps near the electron transport layer. Additional intermediate-wavelength tests (670 and 755 nm) and light field distribution simulation further elucidate the trap distribution. Transient absorption and transient photocurrent also support the non-uniform trap distribution within the chalcogenide-based photodiodes.

Several deep level defects were observed by conventional deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS (LDLTS) in n-type 4H-SiC junction barrier Schottky diodes. We have shown that the broad DLTS peak labeled Z1/2 has, in fact, two components, Z1 and Z2, with activation enthalpies for electron emission of 0.63 eV and 0.68 eV, respectively. The reorientation process between these two components was observed. A combination of double-correlated DLTS and LDLTS demonstrated an anomalous reduction of the emission rate and an increase of the activation enthalpy of Z2 with an increase of the reverse bias applied to the diode. The possible explanation of this phenomenon could be correlated with a tensile stress in epitaxial SiC layers. The results observed are discussed in the frame of the model that correlates Z1 and Z2 with carbon vacancies (VC), located at hexagonal (h) and cubic (k) lattice sites, respectively. We also discussed the origin of other traps E0–E5 with particular emphasis on a N-related shallow donor level located at 0.04 eV below the conduction band, which has never been previously reported by DLTS studies. [ABSTRACT FROM AUTHOR]

We investigated the electrical characterization and defect properties of Ga2O3/SiC hetero-structured Schottky diodes manufactured by mist chemical vapor deposition. For a comprehensive analysis of the impact of post deposition annealing with nitrogen (N2), various characterization techniques were employed, including current density-voltage (J-V), capacitance-voltage (1/C2-V), atomic force microscopy (AFM), and deep level transient spectroscopy (DLTS). The on/off ratios, barrier heights and ideality factors of non-annealed and N2-annealed diodes were investigated using J-V characteristics. It was confirmed that electrical characteristics were improved in the N2-annealed diode. By analyses of 1/C2-V characteristics, the built-in voltage (Vbi) and near surface to bulk carrier concentrations were obtained. Surface topography and roughness, observed through AFM, indicated enhanced crystal quality of the N2-annealed diode. Deep level trap parameters and possible distributions of each trap were extracted from DLTS spectra and Arrhenius plots. The N2-annealing process increased the defects originating from extrinsic impurities at 0.226 eV, while decreasing the traps associated with oxygen vacancies at 0.950 eV and 1.257 eV, which can act as recombination centers. This suggests that the N2-annealing process reduces oxygen vacancies by nitrogen atoms occupying the vacancy sites, leading to a more ordered crystal lattice. Consequently, electrical conductivity, carrier mobility, and overall device performance could be enhanced. [ABSTRACT FROM AUTHOR]

4H-SiC metal-oxide-semiconductor (MOS)-based devices appear to worse electrical performance when exposed to electron irradiation, owing to the production of material defects. This study demonstrates an analysis of defect evolution of 4H-SiC MOS capacitors with the simplest structure, subjected to a series dose of electron irradiation with 10 MeV electron beam, including 30, 50, 100, 500, 1 000 kGy. Deep level transient spectroscopy (DLTS) test and capacitance-voltage (C-V) measurement were used to obtain defects information among MOS samples pre- and post-irradiation. DLTS results present that a low dose of irradiation causes no evident impact on defect evolution near and at the 4H-SiC/SiO2 interface, whereas a high dose of irradiation makes a defect configuration of carbon interstitial dimer defect evolve into another more stable one at a deeper energy level. C-V curves show that different irradiation doses lead to different negative shift degrees of flat-band voltage. This is considered to be resulted from multiple factors, including oxygen vacancies in the SiO2 layer and defects near and at the 4H-SiC/SiO2 interface. This work might be helpful for the development and optimization of 4H-SiC MOS fabrication with respect to anti-irradiation performance. [ABSTRACT FROM AUTHOR]

A border trap (BT) evaluation method was established for SiO2/GeO2/Ge gate stacks by using deep-level transient spectroscopy with a lock-in integrator. Ge metal-oxide-semiconductor capacitors (MOSCAPs) with SiO2/GeO2/Ge gate stacks were fabricated by using different methods. The interface trap (IT) and BT signals were successfully separated based on their different dependences on the intensity of injection pulses. By using p-type MOSCAPs, BTs at the position of 0.4 nm from the GeO2/Ge interface were measured. The energy of these BTs was centralized at the position near to the valence band edge of Ge, and their density (Nbt) was in the range of 1017–1018 cm−3. By using n-type MOSCAPs, BTs at the position range of 2.8–3.4 nm from the GeO2/Ge interface were measured, of which Nbt varied little in the depth direction. The energy of these BTs was distributed in a relatively wide range near to the conduction band edge of Ge, and their Nbt was approximately one order of magnitude higher than those measured by p-MOSCAPs. This high Nbt value might originate from the states of the valence alternation pair with energy close to 1 eV above the conduction band edge of Ge. We also found that Al post metallization annealing can passivate both ITs and BTs near to the valence band edge of Ge but not those near to the conduction band edge. [ABSTRACT FROM AUTHOR]

Defects introduced by low fluence arsenic, antimony, erbium, and bismuth ion implantation have been investigated as a function of annealing temperature using deep level transient spectroscopy (DLTS) and Laplace-DLTS. The defects produced by heavy ion implantation are stable up to higher temperatures than those introduced by electron irradiation and low mass ions. This result is attributed to the enhanced defect interactions that take place in the dense collision cascades created by heavy ion implantation. As a consequence, broadened DLTS features are apparent, especially after annealing. Using high energy resolution Laplace-DLTS, the well-known singly charged divacancy and vacancy-donor pair are accompanied by additional apparent defect signals. This shows that Laplace-DLTS is highly sensitive to the type of damage present, and extreme care must be exercised for reliable Arrhenius analysis. [ABSTRACT FROM AUTHOR]