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The activation of C-H bonds requires the generation of extremely reactive species, which hinders the study of this reaction and its key intermediates. To overcome this challenge, we synthesized an iron(III) chloride-pyridinediimine complex that generates a chlorine radical proximate to reactive C-H bonds upon irradiation with light. Transient spectroscopy confirms the formation of a Cl·|arene complex, which then activates C-H bonds on the PDI ligand to yield HCl and a carbon-centered radical as determined by photocrystallography. First-principles molecular dynamics-density functional theory calculations reveal the trajectory for the formation of a Cl·|arene intermediate. Together, these experimental and computational results show the complete reaction profile for the preferential activation of a C-H bond in the solid state.

Primary defects introduced in boron-doped silicon by an alpha-particle source with a fluence rate of 7 × 106 cm−2 s−1 at cryogenic temperatures were investigated using deep-level transient spectroscopy (DLTS). The data showed that the defects observed between 35 K and 120 K were not detectable when irradiation was carried out at room temperature. The defect levels were observed at 0.10 eV, 0.14 eV and 0.18 eV above the valence band maximum. These levels were attributed to the boron-substitutional vacancy complex, the mono vacancy and a vacancy-related defect respectively.

Time-resolved emission of [Ir(ppy)2dcbpy]Cl (1a, ppy = 2-phenylpyridine, dcbpy = 2,2′-bipyridine-5,5′-dicarboxylic acid) dissolved in DMF revealed a biexponential decay of the excited state. Prior studies on cyclometalated iridium complexes indicated that such dual emission behavior can be attributed to an impurity, compounds that have two LUMO states that are close in energy, or the presence of ion-pairing. To probe each of these effects, a series of homoleptic, Ir(ppy)3 (2), and heteroleptic complexes, [Ir(ppy)2dcbpy]X [X = PF6−(1b), BPh4−(1c)] and [Ir(ppy)2bpy]X [bpy = 2,2′-bipyridine, X = Cl− (3a) PF6−(3b)], were synthesized and photophysically characterized. Among these complexes, only 1a exhibited dual emission with the emission lifetimes of 430 ± 5 ns (80%) and 125 ± 6 ns (20%) in DMF. These lifetimes were further confirmed with the nanosecond transient absorption kinetics, indicating that the dual emission likely did not originate from an impurity. When probing the emission and absorption kinetics of the salts 1b and 1c only one lifetime of 550 ± 10 ns was observed, indicating that the short lifetime of the Cl− salt (1a) comes from a putative ion-paired complex. Density-Functional Theory (DFT) calculations on 1 and 2 fragments in DMF helped uncover the reason behind the ion-pair formation, with carboxyl substituents in 1a causing a loss in electron density on the 3,3′-position of dcbpy. Additionally, the loss in electron density was experimentally validated with 1H NMR, which showed a noticeable downfield shift of the 3,3′-protons in relative to the shifts in 1b and 1c. The data supports that the dual emission observed in 1a is not from two separately emissive states, rather from the dissociated and ion-paired complexes.

Device structures with silicon or germanium nanodots embedded in an oxide matrix may find application in the field of Non-Volatile Memories (NVMs) [1,2] or photonics [3,4]. In the former case, the nanodots can become charged by tunneling of electrons or holes from the silicon substrate through a tunnel oxide. Successful operation requires that the charge does not leak away by the assistance of traps or defects in the material stack. The latter can be probed by techniques like Admittance Spectroscopy [5] or Deep-Level Transient Spectroscopy (DLTS) [2,5]. In the present work we report on a systematic investigation of Metal-Oxide-Semiconductor (MOS) capacitors fabricated on n-type Czochralski silicon substrates and containing Ge nanodots with different size. Ge nanodots with average diameter of 1, 2 or 3 nm have been deposited by Molecular Beam Epitaxy (MBE) on a 5 nm tunnel oxide, thermally grown on n-type Czochralski silicon wafers. An Atomic Force Microscopy (AFM) picture is shown in Fig. 1. Next, 50 nm of SiO2 is deposited. MOS capacitors are prepared by thermal evaporation of 2 mm diameter Al gate contacts, while InGa+In foil ohmic contacts are prepared on the silicon substrate side. The device structure is schematically shown in Fig. 2. Capacitance-Voltage (C-V) characterization is performed at a fixed frequency f=1 MHz, using both a forward and reverse gate voltage sweep. As can be seen in Fig. 3, the presence of the Ge nanodots has a pronounced impact on the C-V characteristics: there is a shift towards positive flat-band voltage, compared with the zero dot reference, a strong increase of the accumulation capacitance and, for the nanodot samples, the hysteresis increases with the increase in nanodot size. For temperature (T-) scan DLTS, the capacitors are mounted in a helium contact gas cryostat cooled with liquid nitrogen. Measurements at different bias pulses from reverse bias (VR) to the pulse bias (VP) are performed in parallel in order to probe the electron traps in different parts of the structure. An example is given in Fig. 4, for the 1 nm nanodots sample. It shows that in deep depletion, there is a broad peak between 150-250 K which could stem from the response of filled interface traps. The increase found at room temperature may originate from minority carrier generation in the depletion region [2,5,6]. When probing closer to the interface, for more positive VR, a pronounced but broad peak around 200 K dominates the spectra. From the Arrhenius plot shown in Fig. 5, it is concluded that it corresponds to the dangling bond (Pb) acceptor level at about 0.31 eV from the conduction band [2,5,6]. Maximum densities are estimated in the range of 5x1011 cm-2eV-1. A comparison of the spectra near the interface for the different samples studied is provided in Fig. 6 and will be discussed in more detail in the conference paper. References [1] S. Tiwari, H. Hanafi, A. Hartstein, E.F. Crabbe and K. Chan, Appl. Phys. Lett., 68, 1377 (1996). [2] R. Beyer, J. von Borany and H. Burghardt, Microelectron. Eng., 86, 1859 (2009). [3] J. von Borany, R. Grötzschel, K.H. Heinig, A. Markwitz, W. Matz, B. Schmidt and W. Skorupa, Appl. Phys. Lett., 71, 3215 (1997). [4] D.A. Grachev, A.V. Ershov, A.V. Belolipetsky, L.V. Krasilnikova, A.N. Yablonskiy, B.A. Andreev and O.B. Gusev, Phys. Stat. Sol. A, 213, 2867 (2016). [5] E. Simoen, J. Lauwaert and H. Vrielinck, Semiconductors and Semimetals, Eds. L. Romano, V. Privitera and C. Jagadish, 91, pp. 205-250, Elsevier 2015. [6] S.N. Volkos, E.S. Efthymiou, S. Bernardini, I.D. Hawkins, A.R. Peaker and G. Petkos, J. Appl. Phys., 100, 124103 (2006). Figure 1

Cesium-based perovskite nanocrystals (NCs) have outstanding photophysical properties improving the performances of lighting devices. Fundamental studies on excitonic properties and hot-carrier dynamics in perovskite NCs further suggest that these materials show higher efficiencies compared to the bulk form of perovskites. However, the relaxation rates and pathways of hot-carriers are still being elucidated. By using ultrafast transient spectroscopy and calculating electronic band structures, we investigated the dependence of halide in Cs-based perovskite (CsPbX3 with X=Br, I, or their mixtures) NCs on the hot-carrier relaxation processes. All samples exhibit ultrafast ( CsPbBr1.5I1.5 (380 fs)>CsPbI3 NC (580 fs). These result accounts for a reduced light emission efficiency of CsPbI3 NC compared to CsPbBr3 NC.

Deep-level transient spectroscopy measurements on β-Ga 2 O 3 crystals reveal the presence of three defect signatures labeled E 2 a, E 2 b, and E 3 with activation energies at around 0.66 eV, 0.73 eV, and 0.95 eV below the conduction band edge. Using secondary ion mass spectrometry, a correlation between the defect concentration associated with E 3 and the Ti concentration present in the samples was found. Particularly, it is found that E 3 is the dominant Ti-related defect in β-Ga 2 O 3 and is associated with a single Ti atom. This finding is further corroborated by hybrid functional calculations that predict Ti substituting on an octahedral Ga site, denoted as Ti GaII, to be a good candidate for E 3. Moreover, the deep level transient spectroscopy results show that the level previously labeled E 2 and attributed to Fe substituting on a gallium site (Fe Ga) consists of two overlapping signatures labeled E 2 a and E 2 b. We tentatively assign E 2 a and E 2 b to Fe substituting for Ga on a tetrahedral or an octahedral site, respectively.

We have studied changes of sub-gap defect states in amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) by means of photoinduced transient spectroscopy (PITS). It is found that the sub-gap states in the channel region of a-IGZO TFTs were drastically modified as back-channel etch process proceeded. The change was due to in-and out-diffusion of hydrogen atoms in the channel region of a-IGZO TFTs, which affects the performance of the a-IGZO TFTs.

Hybrid functional calculations reveal the Zn-O divacancy in ZnO, consisting of adjacent Zn and O vacancies, as an electrically active defect exhibiting charge states ranging from $2+$ to $2-$ within the band gap. Notably, the divacancy retains key features of the monovacancies, namely the negative-\textit{U} behavior of the O vacancy, and the polaronic nature of the Zn vacancy. The thermodynamic charge-state transition levels associated with the negative-\textit{U} behavior $\varepsilon$($0$/$2-$), $\varepsilon$($-$/$2-$) and $\varepsilon$($0$/$-$) are predicted to occur at 0.22, 0.42 and 0.02 eV below the conduction band minimum, respectively, resulting in \textit{U} = $-$0.40 eV. These transition levels are moved closer to the conduction band and the magnitude of \textit{U} is lowered compared to the values for the O vacancy. Further, the interaction with hydrogen has been explored, where it is shown that the divacancy can accommodate up to three H atoms. The first two H atoms prefer to terminate O dangling bonds at the Zn vacancy, while the geometrical location of the third depends on the Fermi-level position. The calculated electrical properties of the divacancy are in excellent agreement with those reported for the E4 center observed by deep-level transient spectroscopy, challenging the O vacancy as a candidate for this level., Comment: 8 pages, 5 figures

An overview is given on how to tackle the question of the electrical activity of extended defects which are inevitably present in hetero-epitaxial III-V layers on silicon. Analysis methods are described which rely on simple device structures containing a specific type of extended defect (here, threading dislocations). Applying the same methods to real scaled FinFETs is rather challenging. Instead Generation-Recombination noise spectroscopy provides data that can be compared with other more standard techniques, like Deep-Level Transient Spectroscopy (DLTS) in order to identify the presence of an electrically active extended defect in the channel material.

The spectrum of defects produced by 5 MeV electron irradiation in oxygen-lean p-type silicon strongly contaminated with interstitial copper (Cui) is studied using the deep-level transient spectroscopy. It is observed that the room-temperature irradiation creates a large amount of CuPL centers (complexes including one substitutional and three interstitial Cu atoms). The analysis shows that this process is govern by formation of the substitutional copper atoms due to the direct reaction between irradiation-induced vacancies and mobile Cui species. This reaction consumes nearly all irradiation-induced vacancies and affects strongly the standard spectrum of radiation defects.

Point defects in n- and p-type 4H-SiC grown by fluorinated chemical vapor deposition (CVD) have been characterized optically by photoluminescence (PL) and electrically by deep-level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS). The results are considered in comparison with defects observed in non-fluorinated CVD growth (e.g., using SiH4 instead of SiF4 as silicon precursor), in order to investigate whether specific fluorine-related defects form during the fluorinated CVD growth, which might prohibit the use of fluorinated chemistry for device-manufacturing purposes. Several new peaks identifying new defects appear in the PL of fluorinated-grown samples, which are not commonly observed neither in other halogenated chemistries, nor in the standard CVD chemistry using silane (SiH4). However, further investigation is needed in order to determine their origin and whether they are related to incorporation of F in the SiC lattice, or not. The electric characterization does not find any new electrically-active defects that can be related to F incorporation. Thus, we find no point defects prohibiting the use of fluorinated chemistry for device-making purposes. Funding Agencies|Knut & Alice Wallenberg Foundation (KAW) project; SSF project "SiC - the Material for Energy-Saving Power Electronics [2016-05362]; VR Grant [2016-05362]

The results of investigations of the pyroelectric current in a layered TlInS2 crystal doped with lanthanum are presented. A comparative analysis of the obtained results and data of photo-induced current transient spectroscopy has been performed. The revealed features of the contribution from electrically active defects to pyroelectric properties of the crystal have been discussed.

Pulsed-laser deposited ZnO thin films were implanted with Ar-ions to generate intrinsic defects within the material. The defects created were analyzed by deep-level and optical deep-level transient spectroscopy. Deep-level defects with thermal activation energies of 980 and appear after implantation. In order to study the annealing behavior of these defects, the implanted samples were isochronously annealed under an oxygen ambient of at temperatures ranging from 120 to . Both defects are annealed out after annealing for 1 h at . (O)DLTS signal of an 40Ar-implanted ZnO thin film under (a) dark condition and (b) under illumination with photons having a wavelength of .

Local electronic states of regular dislocation networks produced by n- and p-type silicon wafer bonding with different screw dislocation density were studied with deep-level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS). A drastic sadden changes of the electric level spectrum with increasing of dislocation density from two shallow bands located near the edges of valence and conduction bands towards two deep bands with energy positions about Ec - (0.22-0.26) eV and Ev + (0.4-0.53) eV were found. The origin of the electric level spectrum changes is ascribed to the changes of dislocation core structure from dissociated to perfect ones that occur when interdislocation distances became comparable with the dislocation equilibrium dissociation width. The obtained results correlate well with the results of recent studies of recombination activity of grain boundaries in mc-Si.

Despite the astonishing values of the power conversion efficiency reached, in just less than a decade, by the carbon nanotube/silicon (CNT/Si) solar cells, many doubts remain on the underlying transport mechanisms across the CNT/Si heterojunction. Here, by combining transient optical spectroscopy in the femtosecond timescale, X-ray photoemission, and a systematic tracking of I–V curves across all phases of the interlayer SiOx growth at the interface, we grasp the mechanism that adequately preserves charge separation at the junction, hindering the photoexcited carrier recombination. Moreover, supported by ab initio calculations aimed to model the complex CNT–Si heterointerface, we show that oxygen-related states at the interface act as entrapping centers for the photoexcited electrons, thus preventing recombination with holes that can flow from Si to CNT across the SiOx layer.

Electrically active defects in silicon-based epitaxial layers on silicon substrates have been studied by Deep-Level Transient Spectroscopy (DLTS). Several aspects have been investigated, like, the impact of the pre-epi cleaning conditions and the effect of a post-deposition anneal on the deep-level properties. It is shown that the pre-cleaning thermal budget has a strong influence on the defects at the substrate/epi layer interface. At the same time, a post-deposition Forming Gas Anneal can passivate to a large extent the active defect states. Finally, it is shown that application of a post-deposition anneal increases the out-diffusion of carbon from a Si:C stressor layer into the p-type CZ substrate.

Formation and annealing behavior of the 1.014-eV copper center and its dissociation product (center) in silicon are characterized by photoluminescence (PL) and deep-level transient spectroscopy (DLTS) measurements. On the basis of the findings reported in this study, the structures of the centers are discussed.

Deep-level transient spectroscopy (DLTS) has been used to study p-n junctions fabricated by implantation of boron into epitaxial 4H-SiC films with n-type conductivity and the donor concentration (8–9) × 1014 cm−3. A DLTS signal anomalous in sign is observed; this signal is related to recharging of deep compensating boron-involved centers in the n-type region near the metallurgical boundary of the p-n junction.

Interaction between hydrogen (H) and irradiation induced defects in p-type silicon (Si) have been studied in H implanted pn-junctions, using deep level transient spectroscopy (DLTS), as well as minority carrier transient spectroscopy (MCTS). Two H related levels at Ev+0.27 eV and Ec-0.32 eV have been observed (Ev and Ec denote the valence and conduction band edge, respectively). Both levels form after a 10 min anneal at 125C, concurrent with the release of H from the boron-hydrogen (B-H) complex. The correlated formation rates and absolute concentrations of the two levels support the notion that they are due to the same defect. In addition, a level at Ec-0.45 eV is observed and discussed in terms of vacancy-hydrogen related defects.

In the present paper, 4H-SiC JBS diodes with "boron" p–n junctions have been investigated by means of deep-level transient spectroscopy (DLTS). The sign of the DLTS signal for all the 4H-SiC diodes under study, was positive. The "anomaly" of the DLTS spectra measured is apparently connected with the properties of "boron" p–n junctions. In particular, is presented the role of deep D-centers in recompensation of donors in the JBS diodes.

Using deep-level transient spectroscopy and capacitance-voltage measurements, the effect of electric field on ionization of the sulfur-related DX center is investigated for n-In1 − xGaxP layers (x = 0.65) grown by vapor-phase epitaxy. It is shown that, upon increasing the electric field strength from 1.3 × 104 to 1.9 × 105 V/cm, the activation energy of the center decreases from ∼0.38 to ∼0.26 eV, and the ionization process is governed by multiphonon tunneling. By the estimated tunneling time of the defect, it is concluded that the DX center corresponds to a model of large lattice relaxation.

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.

Defect levels in the n-type bulk 6H-SiC have been investigated by deep level transient spectroscopy (DLTS) and photoinduced transient spectroscopy (PITS). From the DLTS spectra, four electron traps at Ec - 0.53 eV (T1), Ec - 0.64 eV (T2), Ec - 0.67 eV (T3) and Ec - 0.69 eV (T4) with concentrations of 6.4x1015, 1.1x1016, 3.0x1016 and 1.6x1016 cm–3, respectively, were revealed. The centers T1, tentatively identified with carbon vacancies, were found to be located in the vicinity of dislocations. The centers T2 and T3 were assigned to the known deep-level defect Z1/Z2 occurring both in 4H and 6H SiC polytypes. The PITS measurements revealed two shallow traps with activation energies 20 and 60 meV, as well as a deep trap at 0.66 eV. The origin of the first trap still remains unclear. The latter two traps are tentatively identified with a nitrogen atom in hexagonal site and a complex involving a boron atom and silicon antisite, respectively. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The photophysical properties of mononuclear Pt II chromophores of the general structural formulae: Pt(LL)(C CR) 2 and [Pt(LLL)(C CR)] + (LL = substituted or unsubstituted 2,2′-bipyridine; LLL = substituted or unsubstituted 2,2′:6′,2″-terpyridine; R = aryl or alkyl) are described. Topics related to their preparation, spectroscopy, photochemistry, and photophysics are reviewed.

Deep electronic states associated with iron silicide precipitates have been studied by means of deep-level transient spectroscopy. The observed spectra show the characteristic features of bandlike states at extended defects. From the stability of the states on annealing at moderate temperature they are tentatively attributed to precipitate-matrix interfaces.

Specific on-resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick layers exhibits variations from tens of mW.cm2 to tens of W.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with a literature reported values. Decrease in mobility with the temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples respectively were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy, an influence of shallow boron related levels and D-center on dependence of on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism thus resulting in high Ron.

Capacitance–voltage measurements at 77 and 300 K have shown that 11 keV hydrogen ion implantation of n-Si/SiO 2 structure generates defects in the SiO 2 film and at the Si/SiO 2 interface. Deep-Level Transient Spectroscopy spectra reveal the creation of deep levels in the Si substrate. In the accumulation mode tunnelling type conduction through the 120 nm thick SiO 2 film is observed.

The effect of implantation angle on the profile of the vacancy-phosphorus and divacancy centres (VP/V 2 − ) in n-type 0.7–1.1 Ω cm Cz-grown (1 0 0) Si has been examined using depth profiling with deep-level transient spectroscopy. Samples were mounted with 10° twists from the [1 1 0] direction and various tilts from the [1 0 0] direction then implanted with 600 keV P to a dose of 5×10 8 cm −2 . The peak depth of the VP/V 2 − profile exhibits a systematic variation with the implantation angle: narrowing and increasing in peak concentration as the implantation angle is progressively varied from the aligned direction. The defect profiles are approximately 0.3 μm deeper than the peak in the vacancy profile predicted using the binary collision code Crystal-TRIM. Surface-enhanced annihilation of migrating defects has been considered as the cause of this.

The electrical and optical properties of defects introduced into silicon either by plastic deformation at 630°C or by MeV self-implantation and subsequent annealing at 630°C are compared. It is shown, based on the new experimental results and literature data that most of the deep-level transient spectroscopy (DLTS) lines revealed in the deformed crystals coincide with the DLTS signatures of small interstitial clusters in the dislocation-free implanted/annealed samples. In opposite, the photoluminescence (PL) D1–D4 dislocation bands are observed only in the dislocated crystals.

Defect reactions associated with the elimination of divacancies (V-2) have been studied in n-type Czochralski (Cz) grown and float-zone (FZ) grown Si crystals by means of conventional deep-level transient spectroscopy and high-resolution Laplace deep-level transient spectroscopy (LDLTS). Divacancies were introduced into the crystals by irradiation with 4 MeV electrons. Temperature ranges of the divacancy disappearance were found to be 225-275 degreesC in Cz Si crystals and 300-350 degreesC in FZ Si crystals upon 30 min isochronal annealing. Simultaneously with the V-2 disappearance in Cz Si crystals a correlated appearance of two electron traps with activation energies for electron emission 0.23 eV {E(0.23)} and 0.47 eV {E(0.47)} was observed. It is argued that the main mechanism of the V-2 disappearance in Cz Si crystals is related to the interaction of mobile divacancies with interstitial oxygen atoms. This interaction results in the formation Of V2O centres, which are responsible for the E(0.23) and E(0.47) traps. Electronic properties of the V2O complex were found to be very similar to those of V-2 but energy levels of the two defects could easily be separated using LDLTS. In FZ Si crystals, a few electron traps appeared simultaneously with the V-2 annihilation. The small concentration of these traps compared with the V-2 concentration before annealing prevented their reliable identification. (Less)

Radiation-induced divacancy-related levels in high-purity oxygen-enriched n-type silicon have been studied with the use of deep level transient spectroscopy (DLTS) and Laplace-DLTS. It has been shown that heat treatment at 250°C results in a shift of the divacancy (V 2 )-related peaks observed by 'standard' DLTS. Using Laplace-DLTS it is demonstrated that the shift is due to annealing of V 2 and formation of a new acceptor centre. The new centre has presumably two negative charge states: singly and doubly negative. The formation of the new centre holds a close one-to-one correlation with the annealing of V 2 , indicating that the new centre is a result of divacancy interaction with an impurity or a defect. The close position of the electronic levels of the new centre to that of V 2 suggests a similar electronic and microscopic structure of the new centre to V 2 , and a tentative identification is a divacancy-oxygen centre.

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.

A neural network (NN) method has been proposed as a new algorithm for extraction of defect centers parameters in semi-insulating materials from experimental data obtained by photoinduced transient spectroscopy (PITS). The new algorithm is applied to investigate irradiation-induced defect centers in high resistive silicon. The folds on the PITS spectral surface formed due to the presence of defect levels are best fitted with a two-dimensional approximation function with implementation of the NN learning process. As a result, the Arrhenius plots for defect centers are obtained and the parameters of these centers are determined.

Defects in high quality 4H silicon carbide epilayers have been studied using Deep Level Transient Spectroscopy (DLTS) and Minority Carrier Transient Spectroscopy (MCTS). Both intrinsic defect related centers HS1, Z(1/2). EH6/EH7 and shallow and deep boron centers were found. Electrical properties of the boron related traps are analyzed. Comparison with the optical decay measurements shows that boron is related to the observed lateral variations of the minority carrier lifetime in low doped 4H-SiC epilayers.

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...

High resolution Laplace minority carrier transient spectroscopy (LMCTS) has been used to study defects in gas source molecular beam epitaxy grown Si/Si0.855Ge0.145 strained quantum wells. In LMCTS, the minority carrier emission transient is analysed and detailed emission properties of minority carrier traps which have similar energy can be characterised. The technique was evaluated by comparing LMCTS of a Au : H hole trap, G3, in n-type silicon with Laplace deep level transient spectroscopy of the same trap in p-type silicon. Both techniques confirm that this level consists of two states, as previously suggested in the literature. MCTS was then applied to the n-type Si/SiGe quantum well sample, and five-hole traps were observed. A level at 95 K in the MCTS spectrum was identified as a possible candidate for hole emission from the quantum wells. LMCTS showed that the emission rate of this hole trap exhibited only a slight temperature dependence compared to that exhibited by hole states associated with isolated point defects. This is attributed to holes tunnelling out of the quantum well assisted by the electric field present in the experiment.

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.

Capacitance–voltage measurements and deep-level transient spectroscopy have shown that RF hydrogen plasma treatment of thin (13 nm) SiO 2 /p-Si structures at 20, 100 and 300°C generates defects in the oxide, at the SiO 2 /Si interface and in the near-surface region of Si substrate. The density of these defects depends on the substrate temperature during plasma exposure. The concentration of plasma-induced defects is the highest at 20°C. With increasing treatment temperature the densities of positive oxide charges, donor-like interface traps and deep levels in the Si bulk decrease.

Using deep-level transient spectroscopy (DLTS), we have found that 1 MeV proton bombardment introduces the ER3, nitrogen vacancy related defect, at a rate of 290±50 cm −1 . Further, using capacitance–voltage (C–V) measurements, we have found that 1 MeV protons remove free carriers at a rate of 3880±380 cm −1 . However, when bombarding GaN with 0.5 keV protons, we did not observe the ER3 defect. We propose that 0.5 keV protons indeed introduce the ER3 defect, but that it is passivated by hydrogen.

The defects in a high-resistivity p-GaSe single crystal are investigated by the method of photoinduced current transient spectroscopy. The results show the presence of traps corresponding to the gallium vacancy and extended defects. The traps with thermal-activation energies of 0.13, 0.39, and 0.53 eV are also detected. Their nature is discussed.

Optical transient current spectroscopy (OTCS) has been used to investigate defects in the low-temperature-grown GaAs after postgrowth rapid thermal annealing (RTA). Two samples A and B were grown at 220 degreesC and 360 degreesC on (001) GaAs substrates, respectively. After growth, samples were subjected to 30s RTA in the range of 500-800 degreesC. Before annealing, X-ray diffraction measurements show that the concentrations of the excess arsenic for samples A and B are 2.5 x 10(19) and 1 x 10(19) cm(-3), respectively. It is found that there are strong negative decay signals in the optical transient current (OTC) for the annealed sample A. Due to the influence of OTC strong negative decay signals, it is impossible to identify deep levels clearly from OTCS. For a comparison, three deep levels can be identified for sample B before annealing. They are two shallower deep levels and the so-called As-Ga antisite defect. At the annealing temperature of 600 degreesC, there are still three deep levels. However, their structures are different from those in the as-grown sample. OTC strong negative decay signals are also observed for the annealed sample B. It is argued that OTC negative decay signals are related to arsenic clusters. (C) 2000 Elsevier Science B.V. All rights reserved.

We have considered five different models of charge transfer among coupled defect states in semiconductors where the free-carrier density is limited by the density of unoccupied trap levels, as in the case of defectdominated materials. To determine the time dependence of the trap occupancy features, we formulate a set of coupled differential equations that govern charge capture and emission processes for two defect states. A numerical solution assuming model parameters for traps provides features of the trap occupancy as a function of time. A critical comparison is made in occupancy features for different models, primarily categorized as serial ~hierarchical! and parallel mechanisms of charge transfer. The model predictions are successfully applied to a study of trapping kinetics of defects observed in heavily damaged n-type silicon. We show that, in addition to the occurrence of charge redistribution among multiple traps, the major trap in the damaged silicon exists in two metastable configurations, perhaps with negative U ~Hubbard correlation energy!, and the stable configuration refers to a midgap compensating center related to a small cluster of self-interstitials. The applicability of our model simulations can be extended to more complex defect systems using a combination of these simple models.

The interaction of atomic hydrogen with substitutional palladium impurities is studied in nand p-type Si by deep-level transient spectroscopy. After wet-chemical etching, we determine seven different electrically active and at least one passive palladium hydrogen complex. The levels belong to Pd complexes with different number of hydrogen atoms. The PdH1 complex exhibits one level E(200) at EC20.43 eV. PdH2 has two levels E(60) at EC20.10 eV and H~280! at EV10.55 eV. Four levels are assigned to the PdH3 complex E(160) at EC20.29 eV, H~140! at EV10.23 eV, H~55! at EV10.08 eV, and H~45! at EV10.07 eV. An electrically passive complex is associated with a PdH4 complex. There is great similarity with the correspondent complexes in Pt-doped Si. Annealing above 650 K destroys all hydrogen related complexes and restores the original substitutional Pd concentration.

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...

We review our recent studies on the reactions of hydrogen with transition-metals (Pd, Pt, Ag, and Au) in crystalline Si. Hydrogen was incorporated into the samples by wet-chemical etching. Deep-level transient spectroscopy (DLTS) on Schottky diodes reveals several transition metal‐hydrogen complexes in n- and p-type samples. From DLTS profiling, we are able to estimate the number i of hydrogen atoms in the TM‐Hi complexes. All complexes with i 1, 2 are electrically active. Striking similarities are found for isoelectronic complexes, e.g. Pt‐H2 and Au‐H1. Transition metal complexes with more than three hydrogen atoms are likely to be electrically passive. All hydrogen related complexes disappear after heat treatments above 600 K for several hours. © 1999 Elsevier Science S.A. All rights reserved.

The effect of wet chemical etching and subsequent annealing on the electrical activity of the dislocation-related centers in n-type Si is investigated by the deep-level transient spectroscopy. It is observed that hydrogen penetrates into the samples already during room temperature etching but passivates the dislocation centers only after 300°C annealing. The different dislocation centers exhibit different efficiency of hydrogen passivation. Possible reasons for the observed peculiarities of the dislocation passivation are discussed.

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.

The PICTS technique in conjunction with a highly absorptive excitation wavelength is used to characterize and to distinguish the electron and hole traps in electrodeposited CdTe films. All the deep levels measured are within two deep (donor-type and acceptor-type) energy bands and are related to only native defects and their complexes with chlorine. Except chlorine, no other trace-impurity levels could be detected, implying the effectiveness of electropurification of the bath solution prior to deposition of CdTe. Some results related to the effect of different annealing processes on the spectrum of deep levels are also discussed.