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Strong light–matter coupling to form exciton– and vibropolaritons is increasingly touted as a powerful tool to alter the fundamental properties of organic materials. It is proposed that these states and their facile tunability can be used to rewrite molecular potential energy landscapes and redirect photophysical pathways, with applications from catalysis to electronic devices. Crucial to their photophysical properties is the exchange of energy between coherent, bright polaritons and incoherent dark states. One of the most potent tools to explore this interplay is transient absorption/reflectance spectroscopy. Previous studies have revealed unexpectedly long lifetimes of the coherent polariton states, for which there is no theoretical explanation. Applying these transient methods to a series of strong-coupled organic microcavities, we recover similar long-lived spectral effects. Based on transfer-matrix modeling of the transient experiment, we find that virtually the entire photoresponse results from photoexcitation effects other than the generation of polariton states. Our results suggest that the complex optical properties of polaritonic systems make them especially prone to misleading optical signatures and that more challenging high-time-resolution measurements on high-quality microcavities are necessary to uniquely distinguish the coherent polariton dynamics.

Monolithically integrated $\mathrm{Ga}\mathrm{As}$ $p$-$i$-$n$ diodes are demonstrated on 300-mm $\mathrm{Si}$ $(001)$ substrates using a nanoridge-engineering approach. Deep-level transient spectroscopy (DLTS) is used to perform defect analysis for nanoridge and planar $\mathrm{Ga}\mathrm{As}$ diodes. The point defect, EL2 with ${N}_{T}\ensuremath{\simeq}3\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, is observed for nanoridge $p$-$i$-$n$ diodes. A methodology is developed to extract the surface-state density (${N}_{\mathrm{SS}}$) directly from the DLTS spectrum. $\mathrm{Ga}\mathrm{As}$ nanoridge diodes show ${N}_{\mathrm{SS}}\ensuremath{\simeq}2\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ compared to planar diode approximately $6.5\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. A clear correlation is observed between dark current and defect density. An investigation on the impact of an in situ and ex situ passivation layers on the leakage current reduction is performed for $\mathrm{Ga}\mathrm{As}$ $p$-$i$-$n$ diodes.

Electron traps generated during the reactive ion etching (RIE) process in n-type 4H-SiC are investigated using the deep-level transient spectroscopy technique and isothermal capacitance transient spectroscopy (ICTS) technique. Two electron traps of the Z1/2 center ( EC−0.64eV) and the EH3 center ( EC−0.74eV) are detected in the RIE-etched sample by ICTS measurement at 300 K. A method is proposed to determine the depth profiles of the electron traps that are localized near the etched surface, whereby a depth profile is extracted from the dependence of averaged trap density on the depletion layer width. An exponential distribution is assumed as the depth profile of the electron traps generated during the RIE process. The extracted depth profile was confirmed to be consistent with that determined by the double-correlation method. An appropriate function for the depth profile of carrier traps is assumed and the dependence of the averaged trap density on the depletion layer width is analyzed, which enables the extraction of a depth profile that has both higher depth resolution and higher resolution in the carrier trap density with the proposed method than that with the double-correlation method.

In this study, we demonstrate an approach to identify defects in wide band gap semiconductors by comparing accumulatively-recorded derivative steady-state photo-capacitance (SSPC) spectra to simulations using results from first-principles calculations. Specifically, we present a method to simulate SSPC spectra which adopts inputs both from first-principles calculations and the experimental conditions. The applicability of the developed method is demonstrated using the cases of subsitutional Fe (FeGa) and Ti (TiGa) defects in β-Ga2O3. Using deep-level transient spectroscopy, we identify defect levels associated with Fe GaI 0 / − (E A = 0.66 eV), Fe GaII 0 / − (E A = 0.79 eV) and Ti GaII + / 0 (E A = 1.03 eV) in the β-Ga2O3 samples studied here. Accumulatively-recorded SSPC spectra reveal several defect levels labeled T 1 E F G – T 6 E F G with onsets for optical absorption between 1.5 eV and 4.3 eV. The signature T 1 E F G consists of several overlapping defect signatures, and is identified as being related to Fe GaI 0 / − , Fe GaII 0 / − and Ti GaII + / 0 by comparing measured and simulated accumulatively-recorded derivative SSPC spectra.

Interface traps (ITs) and border traps (BTs) in Al2O3/GeOx/p-Ge gate stacks were characterized using deep-level transient spectroscopy. Through evaluating the gate stacks with different GeOx thicknesses, the respective BTs in Al2O3, the Al2O3/GeOx interface region, and GeOx were detected. The density of ITs (Dit) near the midgap is lower in the metal-oxide-semiconductor (MOS) capacitors with thicker GeOx, while Dit near the valence band is lower in the MOS capacitor with thinner GeOx. The density of BTs (Nbt) in Al2O3 (6–9 × 1017 cm−3) is lower than those in GeOx (∼2 × 1018 cm−3), and the highest Nbt (∼1 × 1019 cm−3) was found in the Al2O3/GeOx interface region. Ge p-channel metal-oxide-semiconductor field-effect-transistors (MOSFETs) with Al2O3/GeOx/p-Ge gate stacks were fabricated and analyzed. We confirmed that the ITs and the BTs near the valence band edge of Ge affect the effective mobility of Ge p-MOSFETs in the high-field region.

Charge transport in π-conjugated polymers is characterized by a strong degree of disorder in both the energy of conjugated segments and the electronic coupling between adjacent sites. This disorder arises from variations in the structure and conformation of molecular units, as well as the weak intermolecular binding interactions. Although disorder in molecular conformation can be expected to influence the density of states (DOS) distribution—and hence, optoelectronic properties of the material—until now, there has been no direct study of the relationship between a distinct conformational defect and the charge transport properties of a conjugated polymer. Here, we investigate the impact of introducing an extended, planarized chain geometry, known as the “β-phase,” on hole transport through otherwise amorphous films of poly(9,9-dioctylfluorene) (PFO). We show that while β-phase introduces a striking drop of about a hundredfold in time-of-flight (TOF) hole mobility (μh) at room temperature, it reduces the steady-state μh measured from hole-only devices by a factor of less than about 5. In order to reconcile these observations, we combine high-dynamic-range TOF photocurrent spectroscopy and energy-resolved electrochemical impedance spectroscopy to extract the hole DOS of the conjugated polymer. Both methods show that the effect of the β-phase content is to introduce a sharp sub-bandgap feature into the DOS of glassy PFO lying about 0.3 eV above the highest occupied molecular orbital. The observed energy of the conformational trap is consistent with electronic structure calculations using a tight-binding approach. Using the obtained DOS with a drift-diffusion model capable of resolving charge carriers in both time and energy, we show how the seemingly contradictory transport phenomena obtained via the time-resolved, frequency-resolved, and steady-state methods are reconciled. The results highlight the significance of energetic redistribution of charge carriers in affecting transport behavior. This work demonstrates how charge-carrier mobility in organic semiconductors can be controlled via molecular conformation, and it resolves a long-standing debate over how different (equilibrium versus nonequilibrium) transport techniques reveal electronic properties of disordered solids in a unified manner., Physical Review X, 9 (2), ISSN:2160-3308

This theoretical–experimental study focuses on the formation of the substitutional-tri-interstitial cluster Cus1Cui3, which has been proposed as the photoluminescence defect CuPL. The configurations and electronic properties of the intermediate defects Cus1Cui1 and Cus1Cui2 are calculated, and their electrically active levels are obtained from conventional and Laplace deep-level transient spectroscopy. The vacancy formation energy near copper-related defects is calculated and found to be much smaller than in the perfect crystal. Then, we show how Cus1Cui3 could become the seed of agglomerates of Cus1Cui3 “units.” The discussion focuses mostly on unanswered questions about the discrepancies between the calculated and measured properties of CuPL and Cus1Cui3.This theoretical–experimental study focuses on the formation of the substitutional-tri-interstitial cluster Cus1Cui3, which has been proposed as the photoluminescence defect CuPL. The configurations and electronic properties of the intermediate defects Cus1Cui1 and Cus1Cui2 are calculated, and their electrically active levels are obtained from conventional and Laplace deep-level transient spectroscopy. The vacancy formation energy near copper-related defects is calculated and found to be much smaller than in the perfect crystal. Then, we show how Cus1Cui3 could become the seed of agglomerates of Cus1Cui3 “units.” The discussion focuses mostly on unanswered questions about the discrepancies between the calculated and measured properties of CuPL and Cus1Cui3.

In this work we present a detailed study of the influence of the GaAs substrate orientation on the electrical properties of heterojunctions based on GaAs and sulfonated polyaniline (SPAN) using Current-Voltage (I-V), Capacitance-Voltage (C-V), Deep-Level Transient Spectroscopy (DLTS) and Laplace DLTS techniques. Three different GaAs substrate orientations have been investigated, namely (1 0 0), (3 1 1)A and (3 1 1)B. The I-V results revealed that the turn-on voltage (Von) of SPAN/(3 1 1)B GaAs heterojunction is higher than that for SPAN/(1 0 0) GaAs and SPAN/(3 1 1)A GaAs heterojunctions. The DLTS results showed that the number of electrically active defects present in devices based on the lower index (1 0 0) plane of GaAs substrate is higher than those of higher index (3 1 1)A and (3 1 1)B GaAs substrates, corroborating with I-V results. In order to investigate the role of interface states, capacitance-frequency measurements were performed in forward bias on all three devices.

While carbon doping is known to increase the resistivity of GaN, highly resistive layers for device isolation can also be obtained by ion implantation. In this study, we report on the electrical characterization of C-implanted n-type homoepitaxial GaN. Our investigation, carried out by capacitance-voltage measurements and deep level/minority carrier transient spectroscopy, revealed the presence of nine majority carrier traps in the 0.2–1.3 eV energy range, below the conduction band edge, and of four minority carrier traps, in the 0.1–1.4 eV energy range, above the valence band edge. The net-donor compensation mechanism and the behavior of defect centers are studied as a function of the annealing temperature in the 100–1000 °C range. While the former is explained in terms of dynamic annealing, the latter is discussed in the light of the present experimental results and those found in the literature.

We investigated trap levels in detector-grade CdZnTe (CZT) material grown by using three different methods, viz, the Bridgman, traveling heater method (THM), and high-pressure Bridgman method (HPB), by current deep-level transient spectroscopy (I-DLTS). All CZT detectors contained deep trap levels located at around 1.1 eV (which we designated DE1), which has been attributed to Te vacancies induced one. However, our crystal growth and characterization results indicated that dislocations induced by Te secondary defects (inclusions/precipitates)were a more probable origin than Te vacancies. Also, a theoretical calculation of the electron de-trapping time associated with DE1 can explain well the abnormal residual current behavior at temperatures slightly above room temperature. Our results show better control of the concentrations and the sizes of Te secondary defects is critical to improving the detector’s performance at room temperature by reducing lagging effects.

In this paper a systematic and detailed study on the photophysical behavior of silicon nanocrystals (alkyl-capped, surface oxidized, oxide-encapsulated) is presented in order to elucidate the influence of local environment and surface species on the luminescence properties. Experiments at different temperatures – ranging from room temperature (RT) to 7 K – confirmed the important influence of the silicon nanocrystal (ncSi) surface on the photoluminescence (PL). Our comparative study of ncSi embedded in different matrices shows a strong increase of the exciton lifetimes at low temperature and the dominant widening of the bandgap for small ncSi after deactivation of traps below 100–150 K. The present findings have significant implications for the use of ncSi in optoelectronic and biomedical applications, since they show that surface oxidation can occur in ligand-capped ncSi which limits the accessible emission wavelength for these applications to the orange/red spectral region when current passivation strategies are used.

Discharge current transient spectroscopy (DCTS) is a promising technique for detecting the trap level and density in dielectrics because it is based on a simple emission process. In order to confirm the validity of DCTS, we compare the results from the conventional deep-level transient spectroscopy (DLTS) technique for samples of CVD-grown silicon nitride (SiNx) films. Results indicated that a trap level, about 0.6 eV below the energy level of the conduction band edge in the SiNx thin films estimated by DCTS is in good agreement with that obtained from DLTS analysis, and it is found that the trap density increases with the decreasing N/Si ratio in the SiNx film. As a proposed estimation for energy level in defects, it will be originated from hydrogen-incorporated defects in the SiNx matrix. This study demonstrates that the DCTS method will be a useful electrical method for the evaluation of defects.

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.

We propose an analysis method for the accurate estimation of the hole trap (H1, E V + 0.85 eV) concentration in n-type GaN via minority carrier transient spectroscopy (MCTS). The proposed method considers both the hole occupation during a filling (current injection) period and the quick carrier recombination via the hole traps near the depletion layer edge immediately after a reverse bias is applied. The reverse bias voltage dependence of the MCTS spectrum indicates that an accurate trap concentration, as well as the hole diffusion length and electron capture cross section of the hole trap, can be determined.

The energy level of electron traps in silicon nitride (SiN x ) thin films was investigated by discharging current transient spectroscopy (DCTS). Results indicate that the trap level of the SiN x thin films becomes deeper with decreasing composition (N/Si) and shallower after hydrogen annealing. The dependence of the trap level on the SiN x composition and the modulation of the trap level by hydrogen annealing are possibly related to the change in the number of Si–H bonds in the SiN x thin films.

The properties of GaAs/AlGaAs solar cells irradiated with 40, 70, 100 and 170 keV protons have been studied. Current–voltage (IV) measurement showed that the worst degradation was found in the cells irradiated by 100 keV protons. The degradation was found defect dependent. Defect profile was obtained by the stopping and range of ions in matter (SRIM) simulation and deep-level transient spectroscopy (DLTS) measurement. In order to obtain the deep-level defect profile in depletion layer by DLTS measurement, the traditional calculation formula of defect concentration has been modified. DLTS measurement showed good agreement with that of the SRIM simulation.

Electrical characteristics and an origin of traps in silicon nitride film were investigated using discharge current transient spectroscopy (DCTS), electron spin resonance (ESR), and photoluminescence (PL). It was found from DCTS that the density of traps of 1.1 eV from the conduction band edge increased with the increase of the gas-mixture ratio of SiH2Cl2 over NH3 for the fabrication of silicon nitride film. The energy levels of traps in silicon nitride film of 0.25, 0.68, 0.83–0.91, and 1.25–1.3 eV from the conduction band edge were found from photoluminescence observation. The ESR signals of the K-center that indicated a silicon dangling-bond increased with the increase of the gas-mixture ratio of SiH2Cl2 over NH3. It is suggested that the origin of traps of 1.1 eV from the conduction band in silicon nitride film is the silicon dangling-bond.

We have investigated the structural and electrical properties of n-type doped Si1− x Ge x epitaxial layers (x = 24–26%) grown by chemical vapor deposition with conventional [SiH2Cl2 (DCS)/GeH4] and high-order (Si2H6/Ge2H6) precursor combinations. X-ray diffraction, atomic force microscopy, and deep-level transient spectroscopy (DLTS) measurements were performed for characterization. The crystalline properties and surface morphology of the Si1− x Ge x layer with Si2H6/Ge2H6 grown at temperatures as low as 550 °C show good structural quality similar to that with DCS/GeH4 grown at 615 °C. On the other hand, in terms of electrical properties, the DLTS measurement reveals the existence of vacancy-related complexes in the as-grown layer with Si2H6/Ge2H6. We found that post-deposition annealing at 200 °C for the Si1− x Ge x epitaxial layer is effective for annihilating vacancy-related defects with densities down to as low as that of conventional precursors.

The gettering behaviors of Fe into Si with and without a p+ layer are investigated by deep-level transient spectroscopy. The samples contaminated with Fe in a wide concentration range were annealed at 600 °C to induce gettering. The surface-layer gettering behaviors of Fe for the sample without the p+ layer strongly depend on the Fe contamination level, in which the surface-layer gettering is not effective for the sample with low-level contamination at a concentration of less than 1 ×1013 cm-3 but effective for the sample with middle-level contamination at a concentration of (1–5) ×1013 cm-3. In contrast, the samples with the p+ layer show effective gettering for low- and middle-level contaminations. The gettering mechanisms of Fe in Si without and with the p+ layer are discussed in detail.

Point defects in n-indium phosphide were studied by deep-level transient spectroscopy (DLTS). A radiation-induced bistable defect is found to form under irradiation of a space-charge region of n-InP Shottky-barrier diodes. The transformations of the defect configuration stimulated by heating, illumination, and current flow are studied.

High-resolution photoinduced transient spectroscopy (HRPITS) has been employed to investigate iron-related point defects produced by electron irradiation in high-resistivity silicon. The measurements revealed 16 traps with activation energies ranging from 14 to 530 meV. From the comparison of results, obtained by the HRPITS and ESR measurements performed on the same samples, a trap positioned at Ev+500 meV was attributed to the iron-vacancy pair (Fei)V and that positioned at EV+530 meV to the vacancy complex with two iron atoms (Fei)2V. The former is found to be stable at 400°C, while the latter anneals out at this temperature similarly to the trap at EV+410 meV related to interstitial iron. As a result of the transformation of the (Fei)2V complex and reactions of the interstitial iron with native defects, new iron-related traps with activation energies of 85, 220 and 380 meV are formed.

An optical-capacitance-transient spectroscopy (O-CTS) method was used to characterize defects in epitaxial 6H-SiC. The O-CTS measurements enable us to estimate the optical ionization energy and the optical cross section of these defects. By the deep level transient spectroscopy (DLTS), three peaks were observed, and two of them were identified as E2 and R centers which have been previously reported. We measured the optical cross section for both the centers. By fitting the experimental data with theoretical curves for the optical cross section, we obtained optical ionization energy of 1.58 eV for the R center and 1.0 eV for the E2 center. From the DLTS measurements, the thermal activation energy of the R center is 1.30 eV and that of the E2 center is 0.43 eV. From these results and the previously reported capture energy barrier, the Franck–Condon shift, dFC is estimated to be 0.28 eV for the R center and 0.62 eV for the E2 center.

In this study, we investigate the influence of wet oxidation after nitridation of a gate oxide on the interface states in SiC metal–oxide–semiconductor field-effect transistors (MOSFETs). We used deep-level transient spectroscopy (DLTS) to clarify the mechanism behind the positive shift in the threshold voltage after wet oxidation without any significant decrease in the mobility. We applied DLTS using a small pulse to obtain the depth profile of the states. We found that the density of deep-level states near the interface on the SiC side increased after wet oxidation at 600 and 800 °C, whereas the density of shallow states did not increase. This result indicates that the increase in the deep-level states is related to the threshold-voltage shift, and there is no degradation in the mobility.

High-temperature isothermal capacitance transient spectroscopy (H-ICTS) measurements were conducted to characterize near mid-gap defects, which are the origin of the memory effect in Ni/p-GaN Schottky contacts. A large single peak was detected only under the forward bias conditions. This indicates that the defects were located in the vicinity of the interface. The change of the peak height and position of the ICTS curves under various bias conditions were qualitatively interpreted by the distribution of the defects and the current flow effect.

Detector-grade undoped chemical vapor deposited (CVD) diamond samples have been studied with thermally stimulated currents (TSC) and photoinduced current transient spectroscopy (PICTS) analyses in the temperature range 300–650 K. Two previously unknown defects have been identified, characterized by activation energies E1=1.14 eV and E2=1.23 eV, cross sections of about σ≈10−13 cm2 and concentrations of Nt≈1016 cm−3. They have been clearly observed by PICTS and isolated in TSC measurements by use of a fractional annealing cycle in the temperature range 300–400 K. Due to their trap parameters, in particular the high cross section, the levels corresponding to E1 and E2 are characterized by capture times of the order of 10–100 ps. A dominant TSC peak observed at ≈500 K has been also investigated and has been resolved into four components with activation energies of the order of 1 eV and cross sections in the range 10−19–10−17 cm2. Three of these levels exhibit a fast capture rate (0.1–10 ns) in spite of their ...

The rapid degradation of Se-doped GaAs0.6P0.4 light-emitting diodes is of prime importance in reliability studies of optical devices using III–V compound semiconductors. Marked changes are observed at the junction of Se-doped GaAs0.6P0.4 light-emitting diodes, because they degrade rapidly, in contrast to Te-doped GaAs0.6P0.4 light-emitting diodes, which degrade gradually. Here, this rapid degradation is investigated using aging tests under various conditions by a capacitance–voltage method and deep-level transient spectroscopy. We discuss the differences in the degradation mechanisms for the two diodes and propose a model for the rapid degradation.

In this paper, the properties of point defects in Cd1−xZnxTe1−ySey (CZTS) radiation detectors are characterized using deep-level transient spectroscopy and compared between materials grown using two different methods, the Bridgman method and the traveling heater method. The nature of the traps was analyzed in terms of their capture cross-sections and trap concentrations, as well as their effects on the measured charge-carrier trapping and de-trapping times, and then compared for the two growth techniques. The results revealed that Se addition to CdZnTe can reduce the VCd− concentration. In Travelling Heater Method (THM) and Bridgman Method (BM) grown CZTS detectors, besides a few similarities in the shallow and medium energy traps, there were major differences in the deep traps. It was observed that the excess-Te and lower growth-temperature conditions in THM-grown CZTS led to a complete compensation of VCd− and two additional traps (attributed to Tei− and TeCd++ appearing at around Ev + 0.26 eV and Ec − ...

Close-spaced vapor transport (CSVT) provides a plausible path to lower the costs of GaAs deposition as it uses only solid precursors and provides precursor utilization in principle approaching 100%. However, the use of H2O as a transport agent causes O to be incorporated in CSVT films, and O has been associated with a number of electrically active defect centers in GaAs, which decrease minority carrier lifetimes. Using deep-level transient spectroscopy, we study the effect of H2O concentration and substrate temperature on electron trap concentrations in n-type GaAs. We find that the most-prominent O-related center (ELO) typically has a much higher concentration than the center usually associated with As antisites (EL2), but that overall defect concentrations can be as low as those in films deposited by common vapor phase techniques. The trends with increasing H2O concentration suggest that ELO is most likely a defect complex with two As antisites. We also consider the optimal conditions for achieving high...

Dislocated Si, SiGe, SiC, and SiGeC n-type heterostructures, grown by molecular beam epitaxy, were characterized by capacitance–voltage profiling and deep-level transient spectroscopy. Exclusively dislocation-related defects were found in the different layers, which correspond to the well-known defects found in plastically deformed silicon.

The electrical activity of the defective states in Er-doped Si has been investigated. The epitaxial layer of Si:Er was grown with the liquid-phase epitaxy method and showed optical emission at 1.54μm. The presence and activity of dislocations have been evidenced by the appearance of lines D1 and D2 in photoluminescence spectra and it has been confirmed by spectroscopic investigations of the existing deep levels, carried out by deep-level transient spectroscopy and optical deep-level transient spectroscopy analyses. We also characterized the defective states by means of charge collection scanning microscopy, namely the electron-beam-induced current (EBIC) and optical-beam-induced current (OBIC) techniaues. The minority-carrier diffusion length has been measured with the EBIC method. OBIC images reveal interesting lattice sites where local emission of charge carriers occurs.

A theory of the transient spectroscopy of quantum well (QW) structures under a large applied bias is presented. An analytical model of the initial part of the transient current is proposed. The time constant of the transient current depends not only on the emission rate from the QWs, as is usually assumed, but also on the subsequent carrier transport across QWs. Numerical simulation was used to confirm the validity of the proposed model, and to study the transient current on a larger time scale. It is shown that the transient current is influenced by the nonuniform distribution of the electric field and related effects, which results in a step-like behavior of the current. A procedure of extraction of the QW emission time from the transient spectroscopy experiments is suggested., 5 pages, 4 figures, to be published in J. Appl. Phys

Photoinduced current transient spectroscopy (PICTS) is used to study deep minority carrier traps in n-type ultrapure germanium (shallow concentration of the order 109 cm−3). In this technique, which is a variant of deep level transient spectroscopy (DLTS), a neutral structure with two ohmic contacts applied on two opposite faces of the sample is illuminated through one of the contacts with intrinsic, strongly absorbed light. The current transients which follow after interrupting the photoexcitation are analyzed using classical double lock-in DLTS resulting in the detection of centers in the minority half of the band gap (provided the back ohmic contact is negative). After correcting the PICTS spectra for the temperature dependence of the mobility, six peaks superimposed on a broad background are clearly resolved. The peaks are the same as the ones found earlier in high-purity n-type germanium (shallow concentration of the order 1010 cm−3) using optical DLTS. These peaks are mainly Cu related. A formula to...

Deep-level transient spectroscopy (DLTS) measurements have been carried out to investigate the deep levels existing in Ti-doped GaAs epilayer grown on GaAs substrates by liquid phase epitaxy. While one hole-trap was observed for the undoped GaAs epilayer, two new traps appeared for the Ti-doped GaAs epilayers. The trap activation energies and the capture cross-sections for the two traps appearing in the Ti-doped GaAs epilayers are 0.2 eV and 3.5×10 −17 cm 2 for the Ti 2+ /Ti 3+ peak, and 0.93 eV and 3.11×10 −15 cm 2 for the Ti 3+ /Ti 4+ peak. These results indicate that the Ti-doped GaAs epilayer forms new defect levels and that the levels restrict the activation of transformed impurities. Furthermore, the present results can help improve the understanding of the applications of Ti-doped GaAs epilayers in electronic devices.

The fluence-dependent properties and the annealing behavior of electron-irradiation-induced deep levels in n-type 6H–SiC have been studied using deep-level transient spectroscopy (DLTS). Sample annealing reveals that the dominant DLTS signal at EC−0.36 eV (labeled as E1 by others) consists of two overlapping deep levels (labeled as ED3L and ED3H). The breakup temperature of the defect ED3L is about 700 °C. The ED3H center together with another deep level located at EC−0.44 eV (so-called E2) can withstand high-temperature annealing up to 1600 °C. It is argued that the involvement of the defect ED3L is the reason that various concentration ratios of E1/E2 were observed in the previous work. The revised value of the capture cross section of the deep-level ED3H has been measured after removing ED3L by annealing. A deep level found at EC−0.50 eV is identified as a vacancy–impurity complex since it was found to have a lower saturated concentration and weak thermal stability. Two other deep levels, EC−0.27 eV an...

The defect states of an electron-beam irradiated GaN epilayer were characterized by capacitance–voltage (C–V) and deep-level transient spectroscopy (DLTS) measurements. The electron irradiation was performed using 1 and 2 MeV energy beams with 1 ×1015 and 1 ×1016 cm-2 doses, respectively. The depth penetrated in the GaN epilayer by 1 MeV electrons appeared to be about 450 to 600 nm from the C–V measurement. Five defect states with activation energies of 0.34, 0.49, and 0.65 eV including two broad signals were observed by DLTS measurements, and it was suggested that they might originate from crystal damage during high-energy electron irradiation.

Photo-induced-current transient spectroscopy and capacitance–voltage measurements on nominally undoped p-CdTe single crystals grown by a Bridgman method have been carried out to investigate the hydrogenation and the annealing effects on the deep levels and on acceptor neutralization. The five hole-traps of the as-grown p-CdTe and their activation energies were E v +0.21 (H 1 ), E v +0.39 (H 2 ), E v +0.43 (H 3 ), E v +0.65 eV (H 4 ), and E v +0.75 (H 5 ). After the p-CdTe was hydrogenated and annealed, H 4 and H 5 related to Cd vacancies disappeared, and the intensity of H 3 related to the native defects decreased by a factor of 2. H 4 and H 5 traps were passivated by the hydrogen atoms. The H 3 defect level is considered to be due to complexes of Cd vacancies and impurities, and the H 2 signal is associated with complexes of shallow impurities. The results of the PICTS measurements showed that hydrogen atoms easily neutralize the Cd vacancies and that the hydrogen atoms are easily separated from the impurities by the thermal energy. These results indicate that the electrical properties of the undoped p-CdTe single crystals are improved by hydrogenation and annealing and that hydrogenated and annealed CdTe crystals hold promise as useful substrates for the growth of Hg x Cd 1 x Te.

We employed capacitance-voltage (C–V) measurements to determine the free-carrier concentration changes in n-GaAs after processing it in a He plasma, and deep-level transient spectroscopy (DLTS) to study the electrical properties of the plasma-induced defects. C–V measurements indicated that He-plasma processing resulted in a strong carrier reduction up to 1 μm below the GaAs surface. DLTS showed that He-ion processing introduced several prominent defects, including the frequently studied radiation-induced defects E1 and E2, associated with VAs. Current-voltage measurements demonstrated that the He-plasma processing inhibits the fabrication of high barrier Schottky diodes on n-GaAs.

Properties of interface states at Ta2O5/n-Si interfaces are studied by capacitance–voltage and deep-level transient spectroscopy (DLTS) measurements. The results show that the “slow” states at Ta2O5/n-Si interfaces are not significantly affected by annealing, and their density is about 1.4–1.9×1011 cm−2. The energy distribution of the “fast” interfacial states in the band gap of silicon is obtained, and some high concentration interfacial states are found. DLTS spectra reveal that the interfacial defects at Ta2O5/n-Si interfaces are all donor type. The high concentration interfacial defects are located at about 0.40 eV below the conduction-band minimum of silicon. Their density decreases with increasing annealing temperature. The origin is suggested to be related to the diffusion of tantalum into the Si substrate.

A thermally stimulated current (TSC) technique has been carried out in order to investigate deep trap properties such as the activation energy and the capture cross section in a neutron-transmutation-doped and thermally annealed GaAs bulk. Two peaks are found near 125 and 185 K in the TSC curve. The trap activation energies and the capture cross sections are 0.23 eV and 9.0 × 10−15 cm2 for the 125 K peak and 0.37 eV and 3.5 × 10−13 cm2 for the 185 K peak, respectively. The values of the activation energy and the capture cross section for the 125 K are in reasonable agreement with those for the EL 14 level obtained from deep-level transient spectroscopy.

The deep levels present in semiconducting CdTe and semi-insulating CdTe:Cl and Cd0.8Zn0.2Te have been investigated by means of cathodoluminescence, deep level transient spectroscopy (DLTS), photo-induced current transient spectroscopy, and photo-DLTS. The latter two methods, which can be applied to semi-insulating materials, allow to characterize the deep traps located up to midgap and can determine whether they are hole or electron traps. We have identified 12 different traps, some common to all the investigated samples, some peculiar to one of them. A comparison of the results obtained from the various materials is given and the status of defect models is reviewed.

We have studied the effect of transient vibrational inversion of population in trans-beta-apo-8'-carotenal on the time-resolved femtosecond stimulated Raman scattering (TR-FSRS) signal. The experimental data are interpreted by applying a quantum mechanical approach, using the formalism of projection operators for constructing the theoretical model of TR-FSRS. Within this theoretical frame we explain the presence of transient Raman losses on the Stokes side of the TR-FSRS spectrum as the effect of vibrational inversion of population. In view of the obtained experimental and theoretical results, we conclude that the excited S-2 electronic level of trans-beta-apo-8'-carotenal relaxes towards the S-0 ground state through a set of four vibrational sublevels of S-1 state. (C) 2014 AIP Publishing LLC.

The capture and emission dynamics of deep levels in GaAs/Ga1-xAlxAs multiple quantum well structures are investigated by using the photoinduced transient spectroscopy technique, In nominally undoped samples three trapping levels with activation energies in the range between 0.4 and 0.8 eV are observed. These are compared with the observations based on other conventional techniques. Large capture cross sections associated with the trapping centers implies that the presence of these can be detrimental for the high speed operation of optoelectronic devices based on GaAs/Ga1-xAlxAs quantum well structures. (C) 1997 American Institute of Physics.

Defects in Si-doped InxAl1−xAs (0

Deep-level transient spectroscopy (DLTS), multi-exponential DLTS and optical DLTS measurements were performed to investigate the deep levels in Si-doped Al x Ga 1 − x As layers grown by molecular beam epitaxy. The results of the DLTS and the multi exponential DLTS measurements showed two DX centers and those of the optical DLTS measurements showed two OX centers. The DX centers originate from the emission of the carriers toward the conduction band and the OX centers are related to the capture of the carriers from the conduction band by the DX centers. These results are in good agreement with the theory in which the levels of the DX centers in Si-doped Al x Ga 1 − x As layers have a capture and emission barrier due to the Si-doping.

Spectra of hole and electron traps of CuInSe2/CdS/ZnO photovoltaic devices have been investigated using deep‐level transient spectroscopy. A decrease of the concentration of shallow electron traps and an increase of the hole trap concentration after an injection of electrons has been observed. The effect is metastable below 200 K. A proposed explanation is based on the idea that both levels belong to the same defect in a different charge state. A resemblance of the phenomena related to that defect and to ‘‘dangling bond’’‐type centers in amorphous semiconductors has been indicated. Some consequences of defect conversion for current transport and performance of photovoltaic devices have been discussed.

The presence and evolution of traps in undoped semi‐insulating (SI) InP obtained by high temperature annealing (900 °C for 90 h) in poor or rich phosphorus atmosphere has been studied by means of photoinduced current transient spectroscopy. Six traps named A1 to A6 having activation energies ranging from 0.2 to 0.6 eV have been detected in three samples submitted to the same annealing process. The samples differ in the Fe concentration of the starting material and the applied phosphorus pressure in the annealing process. A comparison of the corresponding photoinduced current transient spectroscopy spectra shows that among the observed traps, the 0.2 eV one can be related to a phosphorus deficiency, and the 0.3 eV and 0.4 eV traps could be due to an excess of phosphorus during annealing. Moreover, the trap corresponding to iron (0.6 eV) has been observed in all the studied samples.

Contactless capacitance transient techniques have been applied to local mapping of interface traps of a semiconductor wafer. In contactless capacitance transient techniques, a Metal-Air gap-Oxide-Semiconductor (MAOS) structure is used instead of a conventional Metal-Oxide-Semiconductor (MOS) structure. The local mapping of interface traps was obtained by using a contactless Isothermal Capacitance Transient Spectroscopy (ICTS), which is one of the contactless capacitance transient techniques. The validity of the contactless ICTS was demonstrated by characterizing a partially Au-doped Si wafer. The results revealed that local mapping of interface traps using contactless capacitance transient techniques is effective in wafer inspection and is a promising technique for the development of MOS devices and solar cells with high reliability and high performance.

Deep‐level transient spectroscopy has been used to study the properties of electron and hole traps present in n‐type GaAs1−xPx alloys and their evolution versus the alloy composition. An electron trap labeled E0 is observed for all values of the alloy composition x, while a second electron trap E1 appears only for 1≳x≥0.81. As for hole traps one (H2) appears for 1≳x≥0.75, while two others, H0 and H1, are detected for x≥0.81 and for 1≳x≥0.81, respectively. Their ionization energies have been determined and the barriers, associated with electron capture, have been measured in order to determine the energetic position of the two electron traps relative to the conduction band.