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.

The applicability of using Electron Beam Induced Current (EBIC) measurements on Schottky barriers to obtain the mean electron–hole pair creation energy in β-Ga2O3 is reported. It is shown that, when combined with Monte Carlo simulation, this approach yields for Si, GaN, and 4H–SiC a data set consistent with empirical expressions proposed earlier in the literature for many different semiconductors. The method is then applied to β-Ga2O3, where complications related to hole trapping in the material give rise to a strong gain in EBIC and have to be carefully treated and taken into account. When this is done, the mean electron–hole pair energy formation is found to be 15.6 eV, in reasonable agreement with the values predicted by empirical expressions.

Measurements of deep trap spectra in bulk β-Ga2O3 crystals showed the parameters of the two dominant centers with levels near Ec-0.8 eV (E2) and Ec-1 eV(E3) are affected the electric field during deep level transient spectroscopy (DLTS). Both DLTS spectra measurements of the emission rates of the E2 and E3 traps and measurements of emission rates as a function of electric field from capacitance decay curves obtained at a fixed temperature (380 K) show that, for strong electric field with magnitude above ∼5 × 105 V.cm−1, the emission rates of these traps increase with increasing field. For the E2 traps, the increase is driven by phonon assisted tunneling. This points to the trap being an acceptor, which is consistent with reported attribution of the center to substitutional Fe acceptors. For the E3 trap, the field dependence indicates the dominant mechanism is the Poole–Frenkel effect, operable for Coulombic centers. It is concluded that this commonly observed trap is a deep donor.

TlBr is a promising wide-gap semiconductor for developing γ-radiation detectors. One of the limiting factors in developing the technology of detectors is the lack of experimentally determined trapping and recombination centers. In this paper, a generalized model of the formation and behavior of intrinsic defects in pure and doped TlBr single crystals is presented. The relation of intrinsic defects to growth conditions and electrical properties is determined. The previously obtained temperature dependences of the photoconductivity, the data of current deep level transient spectroscopy and microcathodoluminescence, and the kinetic characteristics of the photoconductivity are used as objects of analysis. It is shown that the compensation of charged centers control the transport properties of charge carriers. In compensated doped TlBr crystals, the product of the mobility and lifetime can reach μτ = 5 × 10 −4 cm 2 V −1 . The energy-level diagram of local levels in pure and doped TlBr crystals is proposed. The ionization energies of major structural and impurity defects in TlBr, i.e., the anion vacancy V a + , cation vacancy V c − , and Pb 2+ , O 2− , S 2− ions, are determined. The energy position of a single anion vacancy V a + is E c − 0.22 eV. The energy level of the cation vacancy is E v + 0.85 eV for a single cation vacancy and E v + 0.58 eV for a vacancy incorporated into the {Pb 2+ V c − } 0 complex. The ionization energy of the Pb 2+ Coulomb trap is E c − 0.08 eV in doped TlBr crystals.

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We experimentally investigate surface-plasmon assisted photoemission to enhance the efficiency of metallic photocathodes for high-brightness electron sources. A nanohole array-based copper surface was designed to exhibit a plasmonic response at 800 nm, fabricated using the focused ion beam milling technique, optically characterized and tested as a photocathode in a high power radio frequency photoinjector. Because of the larger absorption and localization of the optical field intensity, the charge yield observed under ultrashort laser pulse illumination is increased by more than 100 times compared to a flat surface. We also present the first beam characterization results (intrinsic emittance and bunch length) from a nanostructured photocathode. DOI: 10.1103/PhysRevLett.110.074801

In this Letter, we report on the efficient generation of electrons from metals using multiphoton photoemission by use of nanostructured plasmonic surfaces to trap, localize, and enhance optical fields. The plasmonic surface increases absorption over normal metals by more than an order of magnitude, and due to the localization of fields, this results in over 6 orders of magnitude increase in effective nonlinear quantum yield. We demonstrate that the achieved quantum yield is high enough for use in rf photoinjectors operating as electron sources for MHz repetition rate x-ray free electron lasers.

Nanometer sized cavities arranged as a subwavelength metallic grating can provide omni-directional and complete absorption of light. We present an explanation of this extraordinary phenomenon as a collective resonant response of a system based on a surface impedance model. This model gives a straightforward way to design systems for optimum light trapping performance and as well gives fundamental insights into the interaction of light with metals at the nanoscale.

Capacitance-voltage (C-V) and capacitance-frequency (C-f) characteristics and admittance spectra were performed in the 85 K–400 K temperature range for AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with Al composition in the AlGaN barrier changing from 20% Al to 50% Al. AC conductance (G) in the C-V characteristics showed a pronounced peak in G-V dependences for voltages corresponding to partial depletion as did G-f dependences taken at these peak voltages. Admittance spectra measured at these voltages reveal peaks in conductance and steps in capacitance with apparent activation energy 0.11–0.13 eV only weakly dependent on Al composition. Theoretical modeling suggests that these features are most likely due to electron transitions from the ground level in the triangular well near the AlN/GaN interface to the quasi continuum of highly excited states in the well with consequent thermal ionization of electrons. For highest Al composition of 50%, additional traps in admittance with activation energy of 0.2 eV and 0.25 eV were detected and this correlated with partial relaxation of strain in the structure as determined by X-ray analysis.

Nanocavities fabricated in a metallic surface have important and technologically useful properties of complete light absorption and strong field enhancement. Here, we demonstrate how a nanometerthick alumina deposition inside such a cavity can be used to gain an exquisite control over the resonance wavelength. This process allows achieving a precise control over the spectral response and is completely reversible allowing many tuning attempts to be made on a single structure until the optimum performance is achieved.

In the resistive phase transition in VO2, temperature excursions taken from points on the major hysteresis loop produce minor loops. For sufficiently small excursions these minor loops degenerate into single-valued, nonhysteretic branches (NHBs) linear in log(ρ) versus T and having essentially the same or even higher temperature coefficient of resistance (TCR) as the semiconducting phase at room temperature. We explain this behavior based on the microscopic picture of percolating phases. Similar short NHBs are found in otherwise hysteretic optical reflectivity. We discuss the opportunities NHBs present for infrared imaging technology based on resistive microbolometers. It is possible to choose a NHB with 102–103 times smaller resistivity than in a pure semiconducting phase, thus providing a microbolometer operating without hysteresis, with low tunable resistivity, and high TCR. Unique features of the proposed method and projected figures of merit are discussed in the context of uncooled focal plane array IR visualization technology.

We used electron paramagnetic resonance (EPR) and deep-level transient spectroscopy (DLTS) to quantitatively compare the concentrations of the EPR signal originally known as SI-5 and the commonly observed DLTS signal at E-c-465 eV in bulk and epitaxial 4H- and 6H-SiC.

A GaAs detector may offer the unique possibility to independently study neutrino properties and solar physics. The ability to measure the flux of p-p, Be-7 and pep solar neutrinos would allow one to approach a solution of the "solar neutrino problem", i.e, the explanation of the significant deficit in observed capture rate of solar neutrinos. A large GaAs solar neutrino detector would allow to measure parameters for possible Mikheyev-Smirnov-Wolfenstein neutrino oscillations with unprecedented precision. A model-independent test for sterile neutrinos is also possible. A direct measurement of the temperature profile of the sun center appears feasible. A GaAs detector would also provide the ability to observe neutral current interactions in addition to addressing a wide range of other interesting physics.In order to measure the p-p, pep and Be-7 neutrinos a detector is required with low threshold (< 350 keV), good energy resolution (< 2 keV) and low background. A GaAs solid-state detector could meet the listed requirements. A large GaAs detector would be composed of approximately 40,000 intrinsic GaAs crystals, each weighting 3.2 kg. Such a detector would have a mass of 125 ton and would contain 60 ton of Ga occupying a volume of roughly 3 m on one side. Previous efforts by many groups have resulted in producing very small detectors with reasonably good resolution. However, it has thus far proved impossible to make large detectors with good resolution. Thus, a solar neutrino detector such as the one described above is obviously very ambitious, but the scientific motivation is sufficiently high that we have begun a research and development program with the goal of determining the technical feasibility of constructing large GaAs crystals with the requisite electronic properties to serve as particle detectors. <(c)> 2001 Elsevier Science B.V. All rights reserved.

Semi-insulating GaAs crystals grown by liquid encapsulated Czochralski technique from Ga-rich melts were evaluated as a possible material for radiation detectors with a high active layer thickness. The density of deep traps, particularly the midgap EL2 donors pinning the Fermi level, was measured by various techniques in conducting and semi-insulating samples. For EL2 traps, a direct evidence of their partial neutralization in the space charge region of reverse biased Schottky diodes due to nonequilibrium capture of electrons is presented for the first time. It is shown that the density of EL2 centers decreases with decreased As composition of the melt very gradually, especially for post-growth annealed samples. Subsequently, if one aims to decrease the EL2 density to such an extent that it would make a serious impact on the depletion layer width in GaAs-based detectors one has to grow semi-insulating GaAs crystals from melts with As composition below about 43% which poses a problem for the preservation of high resistivity of the material due to the relatively high concentration of compensating acceptors.

The results on electrical characteristics and charge collection efficiency in the detectors from bulk SI GaAs developed as a material for solar neutrino spectroscopy are presented. SI GaAs crystals were grown by the Czochralski method. The changes in the stoichiometric components are permanently controlled. It is shown that the performance of GaAs p+–i–n+ structures provided the range of operational reverse voltage up to 1 kV. Measurement of deep level spectra and their analysis reveal the dominant deep levels – hole traps Ev+0.51 and +0.075 eV in GaAs grown from stoichiometric and nonstoichiometric melts, respectively. Investigation of carrier transport properties and bulk homogeneity evinced in charge collection efficiency has shown advantageous results for SI GaAs grown from stoichiometric melt. The reduction of carrier transport parameters and charge collection efficiency in GaAs grown from nonstoichiometric melt is analyzed taking into consideration formation of the hole trap Ev+0.075 eV, presumably assigned to Ga antisite and its influence on the concentration of the ionized deep donor level EL2+.

We describe a method, and the results thereof, for contactless local determination of the excitation energy of recombination centres, their concentration, and the electron and hole capture coefficients in Cd0.3Hg0.7Te. The method suggested is based on analysis of the experimental temperature dependence of electron and hole lifetimes obtained by infrared laser interferometry.

The influence of atomic hydrogen on the recombination activity of defects in indium antimonide was investigated by a contactless interference method which yielded the lifetime of nonequilibrium carriers. A considerable (eightfold) increase in the lifetime was observed in the surface layers of hydrogenated n-type InSb. A very high (compared with other semiconductors) rate of diffusion of hydrogen in InSb was observed.

Hydrogen passivation experiments on nInSb MIS-structures are reported for the first time. No passivation of shallow donors was observed, but after hydrogen treatment a significant decrease in the density of interface surface traps and the density of bulk recombination traps at Ec - 0.1 eV was detected.