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Acceptor levels of the carbon vacancy in 4 <i>H</i> -SiC: Combining Laplace deep level transient spectroscopy with density functional modeling
摘要： We provide direct evidence that the broad Z1/2 peak, commonly observed by conventional deep level transient spectroscopy in as-grown and at high concentrations in radiation damaged 4H-SiC, has two components, namely, Z1 and Z2, with activation energies for electron emissions of 0.59 and 0.67 eV, respectively. We assign these components to Z?1/2 + e? → Z?1/2 → Z?1/2 + 2e? transition sequences from negative-U ordered acceptor levels of carbon vacancy (V_C) defects at hexagonal/pseudo-cubic sites, respectively. By employing short filling pulses at lower temperatures, we were able to characterize the first acceptor level of V_C on both sub-lattice sites. Activation energies for electron emission of 0.48 and 0.41 eV were determined for Z1(?/0) and Z2(?/0) transitions, respectively. Based on trap filling kinetics and capture barrier calculations, we investigated the two-step transitions from neutral to doubly negatively charged Z1 and Z2. Positions of the first and second acceptor levels of V_C at both lattice sites, as well as (?/0) occupancy levels, were derived from the analysis of the emission and capture data.
关键词： density functional theory,acceptor levels,deep level transient spectroscopy,negative-U ordering,carbon vacancy,4H-SiC
更新于2025-09-23 15:23:52
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Investigation of Trap-Induced Threshold Voltage Instability in GaN-on-Si MISHEMTs
摘要： It is shown that an EC–0.90 eV trap in commercial AlGaN/GaN MISHEMTs grown on a Si (111) substrate is responsible for a ?1.8-V threshold voltage (VT) instability using a combination of defect spectroscopy and double-pulsed current–voltage measurements. The EC ? 0.90 eV trap is located in the GaN buffer and is emptied by high drain biases in pinch-off, which raises the trap above the Fermi level in the GaN buffer. This trap also exhibits both fast and slow recovery processes that are explained by the availability of free electrons throughout the depth of the GaN buffer and the trapping process that depletes the free electron concentration. TCAD modeling is used to demonstrate this process and also to show why there is not a significant increase in buffer leakage current after the large negative VT shift due to this trap. This demonstrates that optimizing buffer designs are critical for ideal device performance.
关键词： deep-level transient spectroscopy (DLTS),isothermal,GaN-on-Si,threshold voltage instability,metal-insulator-semiconductor high electron mobility transistors (MISHEMTs),Capture process,trap
更新于2025-09-23 15:22:29
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Electrical characterization of HVPE GaN containing different concentrations of carbon dopants
摘要： A comprehensive study of the electrical characteristics in Schottky diodes made of GaN:C grown by HVPE technology has been reported. The Schottky junctions were made of Ni/Au (25/200 nm) metal stack and ohmic contacts were fabricated by the Ti/Al/Ni/Au (30/90/20/100 nm) e-beam deposition of the metal thin-films followed by the rapid thermal annealing. A good quality of the fabricated Schottky diodes has been proved by considering the transient shape using a pulsed technique of the barrier evaluation under linearly increasing voltage (BELIV). The concentrations of equilibrium carriers of 1×1011 cm-3 and of 2×1010 cm-3 have been evaluated for relatively low and high carbon density doped samples, respectively, using photo-capacitance characteristics dependent on excitation intensity. The effective mobility of carriers of μeff=610 cm2/Vs has been estimated by considering the serial resistance variations dependent on excitation density, through analysis of delay times appeared in formation of peaks within BELIV transients. The optical deep level transient spectroscopy has shown that thermal emission from the rather shallow centres prevails. The centres, ascribed to vacancies as well as to carbon on Ga site, have been identified. It has been demonstrated that Schottky junctions made of heavy carbon doped (NC≥1018 cm-3) HVPE GaN material are capable to withstand voltages of ≥300 V.
关键词： barrier evaluation by linearly increasing voltage pulsed technique,transient current technique,Schottky diodes,carbon doped HVPE GaN grown on Ammono substrates,deep level transient spectroscopy
更新于2025-09-23 15:21:21
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Functional TiO2 interlayer for all-transparent metal-oxide photovoltaics
摘要： Metal oxide has a high energy bandgap and passes the visible light to enlighten the vision to human eyes. However, the strong and harmful UV light is easily captured by large bandgap metal oxide materials. One of the promising applications of metal oxide manipulation would be the transparent solar cells for the transparent window, to guarantee the view of visible light and generate electric power from the invisible UV radiation. Herein, we demonstrate the all-transparent photovoltaics for see-through applications with the functional deployment of TiO2 layer. P-type NiO and n-type ZnO form a heterojunction to establish a photovoltage. TiO2 layer with donor concentration >1019 cm-3 has flat-band potential of 0.4 V vs reversible hydrogen electrode (RHE) and is significantly higher than that of the photoactive ZnO layer, TiO2 layer insertion enables the multifunctions of giving a back surface field and also serving as a carrier selective transport layer. The ultrathin TiO2 embedded ZnO/NiO device has Ag nanowire top electrode and is highly transparent (>50%) in the visible range. This transparent solar cell provides power conversion efficiency of 6.1% and incident photon to charge carrier efficiency of 79.5% under UV light illumination. Mott-Schottky analysis showed the flat band potential to be 0.9 V by using the TiO2 layer insertion to induce the significant higher photovoltage and photocurrent on/off ratio of higher than 5×105 and played a vital role in the enhanced performance of ZnO/NiO heterostructure. We demonstrated the enhancement of the minority carrier lifetime for a broadband of light illumination via back surface field formation and proposed the energy band-diagram. We may suggest that this high transparent photovoltaic device can be functionally applied on-demands of power generation windows of electronic devices, vehicles and building.
关键词： back surface field,interface engineering,all-metal oxides,Transparent photovoltaics,transient spectroscopy
更新于2025-09-19 17:13:59
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A DLTS Perspective on Electrically Active Defects in Plated Crystalline Silicon n <sup>+</sup> p Solar Cells
摘要： Laser ablation (LA) has been compared with standard wet etching for contact opening in crystalline silicon n+p solar cells, from a perspective of electrically active defects, assessed by Deep-Level Transient Spectroscopy (DLTS). Copper metallization is employed, including a plated nickel diffusion barrier. It is shown that a hole trap around 0.17 eV above the valence band is systematically present in the depletion region of the junctions, irrespective of the contact opening method. This level could correspond with the substitutional nickel donor level in silicon and indicates that Ni in-diffusion occurs during the contact processing. No clear evidence for the presence of electrically active copper has been found. In addition, two other hole traps H2 and H3, belonging to point defects, have been observed after wet etching and standard LA, while for the highest laser power (hard LA) a broad band develops around 175 K, which is believed to be associated with dislocations, penetrating the p-type base region. Evidence will also be given for the impurity decoration of the dislocations, which enhances their electrical activity.
关键词： Deep-Level Transient Spectroscopy (DLTS),copper metallization,electrically active defects,laser ablation,nickel diffusion barrier,wet etching,crystalline silicon n+p solar cells
更新于2025-09-11 14:15:04
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Understanding structure-activity relationships in linear polymer photocatalysts for hydrogen evolution
摘要： Conjugated polymers have sparked much interest as photocatalysts for hydrogen production. However, beyond basic considerations such as spectral absorption, the factors that dictate their photocatalytic activity are poorly understood. Here we investigate a series of linear conjugated polymers with external quantum efficiencies for hydrogen production between 0.4 and 11.6%. We monitor the generation of the photoactive species from femtoseconds to seconds after light absorption using transient spectroscopy and correlate their yield with the measured photocatalytic activity. Experiments coupled with modeling suggest that the localization of water around the polymer chain due to the incorporation of sulfone groups into an otherwise hydrophobic backbone is crucial for charge generation. Calculations of solution redox potentials and charge transfer free energies demonstrate that electron transfer from the sacrificial donor becomes thermodynamically favored as a result of the more polar local environment, leading to the production of long-lived electrons in these amphiphilic polymers.
关键词： photocatalysts,transient spectroscopy,hydrogen production,sulfone groups,conjugated polymers
更新于2025-09-10 09:29:36
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Charge transient behaviour and spectroscopic ellipsometry characteristics of TiN/HfSiO MOS capacitors
摘要： A combination of two powerful techniques, namely, charge Deep level transient spectroscopy and spectroscopic ellipsometry is employed on atomic layer deposited Si-metal oxide semiconductor capacitors (MOSCAPs) to investigate the energy ef?ciency of the physical process. Ultra-thin TiN/HfSiO acted as gate-dielectric stack on Si substrate was carefully subjected to rapid thermal processing and subsequent spectroscopic measurements to determine the transient behaviour of charges and electro-optical characteristics. Some key parameters such as trap concentration, activation energy required to surmount the traps, capture cross section, refractive index and extinction coef?cient are found to play an important role in order to assess the energy ef?ciency of the devices both in terms of post-process quality of the retained surface and residual ef?ciency of the process by virtue of dynamics at atomistic scales. The results may provide a useful insight to the Si manufacturing protocols at ever decreasing nodes with desirable energy ef?ciency.
关键词： energy efficiency,charge Deep level transient spectroscopy,MOSCAPs,spectroscopic ellipsometry,TiN/HfSiO
更新于2025-09-10 09:29:36
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Ultrafast formation and dynamics of interlayer exciton in a large-area CVD-grown WS <sub/>2</sub> /WSe <sub/>2</sub> heterostructure
摘要： A WS2/WSe2 heterostructure is constructed by stacking a WS2 monolayer on the top of WSe2 monolayer fabricated with chemical vapor deposition (CVD) method. Ultrafast transient spectroscopy is used to demonstrate the ultrafast charge transfer and interlayer exciton dynamics in the heterostructure. When the WS2/WSe2 heterostructure was photoexcitated at 617 nm (2.01 eV) to excite the A-exciton transition of WS2, an ultrafast photobleaching was observed around the WSe2 A-exciton transition at 749 nm. The bleaching signal lasts several nanoseconds, which is much longer than the A-exciton lifetime in both the WS2 and WSe2 monolayer film. Moreover, by selectively photoexciting the A-exciton of WSe2 at 749 nm in the heterostructure, an ultrafast photobleaching occurs around the WS2 A-exciton transition, the recovery of the bleaching shows a single exponential relaxation with typical time constant of ~1.8 ps. The very fast relaxation in the heterostructure probing around 620 nm is indicative that rich defect states exist below the conduction band in WS2, which can efficiently trap these electrons transferred from the WSe2 upon photoexcitation. Our spectroscopic results reveal that our CVD-grown WS2/WSe2 bilayer film has a type II heterostructure in nature at room temperature. With photoexcitation, electrons and holes can be separately confined in the WS2 and WSe2 layer, respectively; as a result, interlayer excitons are formed.
关键词： charge transfer,interlayer exciton,type-II heterostructure,transition metal dichalcogenides,transient spectroscopy
更新于2025-09-10 09:29:36
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Border trap evaluation for SiO <sub/>2</sub> /GeO <sub/>2</sub> /Ge gate stacks using deep-level transient spectroscopy
摘要： 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.
关键词： deep-level transient spectroscopy,valence band edge,conduction band edge,interface trap,border trap,Ge metal-oxide-semiconductor capacitors
更新于2025-09-09 09:28:46