Universal radiation tolerant semiconductor

Radiation tolerance is determined as the ability of crystalline materials to withstand the accumulation of the radiation induced disorder. Nevertheless, for sufficiently high fluences, in all by far known semiconductors it ends up with either very high disorder levels or amorphization. Here we show that gamma/beta (γ/β) double polymorph Ga2O3 structures exhibit remarkably high radiation tolerance. Specifically, for room temperature experiments, they tolerate a disorder equivalent to hundreds of displacements per atom, without severe degradations of crystallinity; in comparison with, e.g., Si amorphizable already with the lattice atoms displaced just once. We explain this behavior by an interesting combination of the Ga- and O- sublattice properties in γ-Ga2O3. In particular, O-sublattice exhibits a strong recrystallization trend to recover the face-centered-cubic stacking despite the stronger displacement of O atoms compared to Ga during the active periods of cascades. Notably, we also explained the origin of the β-to-γ Ga2O3 transformation, as a function of the increased disorder in β-Ga2O3 and studied the phenomena as a function of the chemical nature of the implanted atoms. As a result, we conclude that γ/β double polymorph Ga2O3 structures, in terms of their radiation tolerance properties, benchmark a class of universal radiation tolerant semiconductors.

Optical properties of ZnFe2O4 nanoparticles and Fe-decorated inversion domain boundaries in ZnO

The maximum efficiency of solar cells utilizing a single layer for photovoltaic conversion is given by the single junction Shockley-Queisser limit. In tandem solar cells, a stack of materials with different band gaps contribute to the conversion, enabling tandem cells to exceed the single junction Shockley-Queisser limit. An intriguing variant of this approach is to embed semiconducting nanoparticles in a transparent conducting oxide (TCO) solar cell front contact. This alternative route would enhance the functionality of the TCO layer, allowing it to participate directly in photovoltaic conversion via photon absorption and charge carrier generation in the nanoparticles. Here, we demonstrate the functionalization of ZnO through incorporation of either ZnFe2O4 spinel nanoparticles (NPs) or inversion domain boundaries (IDBs) decorated by Fe. Diffuse reflectance spectroscopy and electron energy loss spectroscopy show that samples containing spinel particles and samples containing IDBs decorated by Fe both display enhanced absorption in the visible range at around 2.0 and 2.6 eV. This striking functional similarity was attributed to the local structural similarity around Fe-ions in spinel ZnFe2O4 and at Fe-decorated basal IDBs. Hence, functional properties of the ZnFe2O4 arise already for the two-dimensional basal IDBs, from which these planar defects behave like two-dimensional spinel-like inclusions in ZnO. Cathodoluminescence spectra reveal an increased luminescence around the band edge of spinel ZnFe2O4 when measuring on the spinel ZnFe2O4 NPs embedded in ZnO, whereas spectra from Fe-decorated IDBs could be deconvoluted into luminescence contributions from bulk ZnO and bulk ZnFe2O4.

Gettering in PolySi/SiOx Passivating Contacts Enables Si-Based Tandem Solar Cells with High Thermal and Contamination Resilience

Multijunction solar cells in a tandem configuration could further lower the costs of electricity if crystalline Si (c-Si) is used as the bottom cell. However, for direct monolithic integration on c-Si, only a restricted number of top and bottom cell architectures are compatible, due to either epitaxy or high-temperature constraints, where the interface between subcells is subject to a trade-off between transmittance, electrical interconnection, and bottom cell degradation. Using polySi/SiO_x passivating contacts for Si, this degradation can be largely circumvented by tuning the polySi/SiO_x stacks to promote gettering of contaminants admitted into the Si bottom cell during the top cell synthesis. Applying this concept to the low-cost top cell chalcogenides Cu₂ZnSnS₄ (CZTS), CuGaSe₂ (CGSe), and AgInGaSe₂ (AIGSe), fabricated under harsh S or Se atmospheres above 550 °C, we show that increasing the heavily doped polySi layer thickness from 40 to up to 400 nm prevents a reduction in Si carrier lifetime by 1 order of magnitude, with final lifetimes above 500 μs uniformly across areas up to 20 cm². In all cases, the increased resilience was correlated with a 99.9% reduction in contaminant concentration in the c-Si bulk, provided by the thick polySi layer, which acts as a buried gettering layer in the tandem structure without compromising the Si passivation quality. The Si resilience decreased as AIGSe > CGSe > CZTS, in accordance with the measured Cu contamination profiles and higher annealing temperatures. An efficiency of up to 7% was achieved for a CZTS/Si tandem, where the Si bottom cell is no longer the limiting factor.

Formation and functionalization of Ge-nanoparticles in ZnO

Semiconductor nanocrystals are often proposed as a viable route to improve solar energy conversion in photovoltaics and photoelectrochemical systems. Embedding the nanocrystals in, e.g. a transparent and conducting electrode of a solar cell will promote the photon absorption and subsequent transfer of the generated charge carriers from the nanocrystal, and thereby enhance the function of the electrode. This can be accomplished by embedding a semiconducting nanocrystal with a small bandgap in a transparent conducting oxide (TCO), which is commonly utilized as electrode in new generation solar cells. Here, we demonstrate the incorporation, formation, and functionalization of germanium (Ge) nanocrystals in zinc oxide utilizing ion implantation, where post implantation annealing at 800 °C results in diamond cubic Ge nanocrystals with sizes between 2 and 20 nm. Photoluminecence spectra show a distinct emission around 0.7 eV arising from the Ge nanocrystals, and with additional emission features up to 1.15 eV due to quantum confinement, demonstrating a novel functionalization and tunability of the TCO electrode.

Strain Modulation of Si Vacancy Emission from SiC Micro- and Nanoparticles

Single-photon emitting point defects in semiconductors have emerged as strong candidates for future quantum technology devices. In the present work, we exploit crystalline particles to investigate relevant defect localizations, emission shifting, and waveguiding. Specifically, emission from 6H-SiC micro- and nanoparticles ranging from 100 nm to 5 μm in size is collected using cathodoluminescence (CL), and we monitor signals attributed to the Si vacancy (VSi) as a function of its location. Clear shifts in the emission wavelength are found for emitters localized in the particle center and at the edges. By comparing spatial CL maps with strain analysis carried out in transmission electron microscopy, we attribute the emission shifts to compressive strain of 2-3% along the particle a-direction. Thus, embedding VSi qubit defects within SiC nanoparticles offers an interesting and versatile opportunity to tune single-photon emission energies while simultaneously ensuring ease of addressability via a self-assembled SiC nanoparticle matrix.

Experimental exploration of the amphoteric defect model by cryogenic ion irradiation of a range of wide band gap oxide materials

The evolution of electrical resistance as function of defect concentration is examined for the unipolarn-conducting oxides CdO,β-Ga₂O₃, In₂O₃, SnO₂and ZnO in order to explore the predictions of the amphoteric defect model. Intrinsic defects are introduced by ion irradiation at cryogenic temperatures, and the resistance is measured in-situ by current-voltage sweeps as a function of irradiation dose. Temperature dependent Hall effect measurements are performed to determine the carrier concentration and mobility of the samples before and after irradiation. After the ultimate irradiation step, the Ga₂O₃and SnO₂samples have both turned highly resistive. In contrast, the In₂O₃and ZnO samples are ultimately found to be less resistive than prior to irradiation, however, they both show an increased resistance at intermediate doses. Based on thermodynamic defect charge state transitions computed by hybrid density functional theory, a model expanding on the current amphoteric defect model is proposed.

Persistent Double-Layer Formation in Kesterite Solar Cells: A Critical Review

In kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cell research, an asymmetric crystallization profile is often obtained after annealing, resulting in a bilayered - or double-layered - CZTSSe absorber. So far, only segregated pieces of research exist to characterize the appearance of this double layer, its formation dynamics, and its effect on the performances of devices. In this work, we review the existing research on double-layered kesterites and evaluate the different mechanisms proposed. Using a cosputtering-based approach, we show that the two layers can differ significantly in morphology, composition, and optoelectronic properties and complement the results with a large statistical data set of over 850 individual CZTS solar cells. By reducing the absorber thickness from above 1000 to 300 nm, we show that the double-layer segregation is alleviated. In turn, we see a progressive improvement in the device performance for lower thickness, which alone would be inconsistent with the well-known case of ultrathin CIGS solar cells. We therefore attribute the improvements to the reduced double-layer occurrence and find that the double layer limits the efficiency of our devices to below 7%. By comparing the results with CZTS grown on monocrystalline Si substrates, without a native Na supply, we show that the alkali metal supply does not determine the double-layer formation but merely reduces the threshold for its occurrence. Instead, we propose that the main formation mechanism is the early migration of Cu to the surface during annealing and formation of Cu_2-xS phases in a self-regulating process akin to the Kirkendall effect. Finally, we comment on the generality of the mechanism proposed by comparing our results to other synthesis routes, including our own in-house results from solution processing and pulsed laser deposition of sulfide- and oxide-based targets. We find that although the double-layer occurrence largely depends on the kesterite synthesis route, the common factors determining the double-layer occurrence appear to be the presence of metallic Cu and/or a chalcogen deficiency in the precursor matrix. We suggest that understanding the limitations imposed by the double-layer dynamics could prove useful to pave the way for breaking the 13% efficiency barrier for this technology.

Transition-Metal Oxides for Kesterite Solar Cells Developed on Transparent Substrates

Fabrication on transparent soda-lime glass/fluorine-doped tin oxide (FTO) substrates opens the way to advanced applications for kesterite solar cells such as semitransparent, bifacial, and tandem devices, which are key to the future of the PV market. However, the complex behavior of the p-kesterite/n-FTO back-interface potentially limits the power conversion efficiency of such devices. Overcoming this issue requires careful interface engineering. This work empirically explores the use of transition-metal oxides (TMOs) and Mo-based nanolayers to improve the back-interface of Cu₂ZnSnSe₄, Cu₂ZnSnS₄, and Cu₂ZnSn(S,Se)₄ solar cells fabricated on transparent glass/FTO substrates. Although the use of TMOs alone is found to be highly detrimental to the devices inducing complex current-blocking behaviors, the use of Mo:Na nanolayers and their combination with n-type TMOs TiO₂ and V₂O₅ are shown to be a very promising strategy to improve the limited performance of kesterite devices fabricated on transparent substrates. The optoelectronic, morphological, structural, and in-depth compositional characterization performed on the devices suggests that the improvements observed are related to a combination of shunt insulation and recombination reduction. This way, record efficiencies of 6.1, 6.2, and 7.9% are obtained for Cu₂ZnSnSe₄, Cu₂ZnSnS₄, and Cu₂ZnSn(S,Se)₄ devices, respectively, giving proof of the potential of TMOs for the development of kesterite solar cells on transparent substrates.

Formation of N2 bubbles along grain boundaries in (ZnO)1-x(GaN)x: nanoscale STEM-EELS studies

Direct evidence of N₂ formation after annealing of (ZnO)_1-x(GaN)_x alloys was revealed. N₂ was trapped by V_Zn+Ga-clusters, forming faceted voids along grain boundaries. This study shows that N-N bonding is a competitive path for nitrogen after annealing, in addition to the increasing Ga-N bonds, indicating that N in O substitution sites (N_O) is not a stable configuration.

Optical signatures of single ion tracks in ZnO

The optical properties of single ion tracks have been studied in ZnO implanted with Ge by combining depth-resolved hyperspectral cathodoluminescence (CL) and photoluminescence (PL) spectroscopy techniques. The results indicate that ZnO is susceptible to implantation doses as low as 10⁸ to 10⁹ cm^-2. We demonstrate that the intensity ratio of ionized and neutral donor bound exciton emissions [D⁺X/D⁰X] can be used as a tracer for a local band bending both at the surface as well as in the crystal bulk along the ion tracks. The hyperspectral CL imaging performed at 80 K with 50 nm resolution over the regions with single ion tracks permitted direct assessment of the minority carrier diffusion length. The radii of distortion and space charge surrounding single ion tracks were estimated from the 2D distributions of defect-related green emission (GE) and excitonic D⁺X emission, both normalized with regard to neutral D⁰X emission, i.e., from the [GE/D⁰X] and [D⁺X/D⁰X] ratio maps. Our results indicate that single ion tracks in ZnO can be resolved up to ion doses of the order of 5 × 10⁹ cm^-2, in which defect aggregation along the extended defects obstructs signatures of individual tracks.

First-principles calculations of Stark shifts of electronic transitions for defects in semiconductors: the Si vacancy in 4H-SiC

Point defects in solids are promising single-photon sources with application in quantum sensing, computing and communication. Herein, we describe a theoretical framework for studying electric field effects on defect-related electronic transitions, based on density functional theory calculations with periodic boundary conditions. Sawtooth-shaped electric fields are applied perpendicular to the surface of a two-dimensional defective slab, with induced charge singularities being placed in the vacuum layer. The silicon vacancy (V _Si) in 4H-SiC is employed as a benchmark system, having three zero-phonon lines in the near-infrared (V1, V1' and V2) and exhibiting Stark tunability via fabrication of Schottky barrier or p-i-n diodes. In agreement with experimental observations, we find an approximately linear field response for the zero-phonon transitions of V _Si involving the decay from the first excited state (named V1 and V2). However, the magnitude of the Stark shifts are overestimated by nearly a factor of 10 when comparing to experimental findings. We discuss several theoretical and experimental aspects which could affect the agreement.

High electron mobility single-crystalline ZnSnN2 on ZnO (0001) substrates

Making a systematic effort, we have developed single-crystalline ZnSnN₂ on ZnO (0001) by reactive magnetron co-sputtering.

Role of Nitrogen in Defect Evolution in Zinc Oxide: STEM-EELS Nanoscale Investigations

Direct evidence of the formation of nitrogen molecules (N₂) after ion implantion of ZnO has been revealed by an atomically resolved scanning transmission electron microscopy (STEM)-electron energy-loss spectroscopy (EELS) investigation. Taking advantage of the possibility of using multiple detectors simultaneously in aberration-corrected STEM, we utilize the detailed correlation between the atomic structure and chemical identification to develop a model explaining the formation and evolution of different defect types and their interaction with N. In particular, the formation of zinc vacancy (V_Zn) clusters filled with N₂ after heat treatment at 650 °C was observed, clearly indicating that N has not been stabilized in the O substitution site, thus limiting p-type doping. Previous results showing an exceptional thermal stability of vacancy clusters only for the case of N-doped ZnO are supported. Furthermore, V_Zn-N₂ stabilization leads to suppression of V_Zn-Zn_i recombination; hence, the highly mobile Zn interstitials preferentially condense on the basal planes promoting formation of extended defects (basal stacking faults and stacking mismatched boundaries). The terminations of these defects provide energetically favorable sites for further N₂ trapping as a way to reduce local strain fields.

Structural and optical properties of individual Zn2GeO4 particles embedded in ZnO

Functionalizing transparent conducting oxides (TCOs) is an intriguing approach to expand the tunability and operation of optoelectronic devices. For example, forming nanoparticles that act as quantum wells or barriers in zinc oxide (ZnO), one of the main TCOs today, may expand its optical and electronic tunability. In this work, 800 keV Ge ions have been implanted at a dose of 1 × 10¹⁶ cm^-2 into crystalline ZnO. After annealing at 1000 °C embedded disk-shaped particles with diameters up to 100 nm are formed. Scanning transmission electron microscopy shows that these are particles of the trigonal Zn₂GeO₄ phase. The particles are terminated by atomically sharp facets of the type {11 [Formula: see text] 0}, and the interface between the matrix and particles is decorated with misfit dislocations in order to accommodate the lattice mismatch between the two crystals. Electron energy loss spectroscopy has been employed to measure the band gap of individual nanoparticles, showing an onset of band-to-band transitions at 5.03 ± 0.02 eV. This work illustrates the advantages of using STEM characterization methods, where information of structure, growth, and properties can be directly obtained.

ZnCr₂O₄ Inclusions in ZnO Matrix Investigated by Probe-Corrected STEM-EELS

The ZnCr₂O₄/ZnO materials system has a wide range of potential applications, for example, as a photocatalytic material for waste-water treatment and gas sensing. In this study, probe-corrected high-resolution scanning transmission electron microscopy and geometric phase analysis were utilized to study the dislocation structure and strain distribution at the interface between zinc oxide (ZnO) and embedded zinc chromium oxide (ZnCr₂O₄) particles. Ball-milled and dry-pressed ZnO and chromium oxide (α-Cr₂O₃) powder formed ZnCr₂O₄ inclusions in ZnO with size ~400 nm, where the interface properties depended on the interface orientation. In particular, sharp interfaces were observed for ZnO [2113]/ZnCr₂O₄ [110] orientations, while ZnO [1210]/ZnCr₂O₄ [112] orientations revealed an interface over several atomic layers, with a high density of dislocations. Further, monochromated electron energy-loss spectroscopy was employed to map the optical band gap of ZnCr₂O₄ nanoparticles in the ZnO matrix and their interface, where the average band gap of ZnCr₂O₄ nanoparticles was measured to be 3.84 ± 0.03 eV, in contrast to 3.22 ± 0.01 eV for the ZnO matrix.

Highly Correlated Hydride Ion Tracer Diffusion in SrTiO3- xH x Oxyhydrides

Mixed oxide hydride anion systems constitute a novel class of materials exhibiting intriguing properties such as solid-state hydride ion conduction and fast anion exchange. In this contribution we derive the kinetics of hydride ion transport in a mixed oxide-hydride system, SrTiO_{3- x}H _x, through isotope exchange and depth profiling. Density functional theory (DFT) calculations indicate that migration of H^- to neighboring vacant oxygen lattice sites is fast, but that long-range transport is impeded by slow reorganization of the oxygen sublattice. From measured hydride tracer-diffusion coefficients and the correlation factors derived from DFT, we are able to derive the hydrogen self-diffusion coefficients in SrTiO_{3- x}H _x. More generally, the explicit description of hydride ion transport in SrTiO_{3- x}H _x through combination of experimental and computational methods reported in this work can be applied to explore anion diffusion in other mixed anion systems.

Electrical conductivity of In2O3 and Ga2O3 after low temperature ion irradiation; implications for instrinsic defect formation and charge neutrality level

The evolution of sheet resistance of n-type In₂O₃ and Ga₂O₃ exposed to bombardment with MeV ¹²C and ²⁸Si ions at 35 K is studied in situ. While the sheet resistance of Ga₂O₃ increased by more than eight orders of magnitude as a result of ion irradiation, In₂O₃ showed a more complex defect evolution and became more conductive when irradiated at the highest doses. Heating up to room temperature reduced the sheet resistivity somewhat, but Ga₂O₃ remained highly resistive, while In₂O₃ showed a lower resistance than as deposited samples. Thermal admittance spectroscopy and deep level transient spectroscopy did not reveal new defect levels for irradiation up to [Formula: see text] cm^-2. A model where larger defect complexes preferentially produce donor like defects in In₂O₃ is proposed, and may reveal a microscopic view of a charge neutrality level within the conduction band, as previously proposed.

Diffusivity of the double negatively charged mono-vacancy in silicon

Lightly-doped silicon (Si) samples of n-type conductivity have been irradiated with 2.0 MeV [Formula: see text] ions at a temperature of 30 K and characterized in situ by deep level transient spectroscopy (DLTS) measurements using an on-line setup. Migration of the Si mono-vacancy in its double negative charge state (V ^2-) starts to occur at temperatures above  ∼70 K and is monitored via trapping of V ^2- by interstitial oxygen impurity atoms ([Formula: see text]), leading to the growth of the prominent vacancy-oxygen ([Formula: see text]) center. The [Formula: see text] center gives rise to an acceptor level located at  ∼0.17 eV below the conduction band edge (E _c ) and is readily detected by DLTS measurements. Post-irradiation isothermal anneals at temperatures in the range of 70 to 90 K reveal first-order kinetics for the reaction [Formula: see text] in both Czochralski-grown and Float-zone samples subjected to low fluences of [Formula: see text] ions, i.e. the irradiation-induced V concentration is dilute ([Formula: see text]10¹³ cm^-3). On the basis of these kinetics data and the content of [Formula: see text], the diffusivity of V ^2- can be determined quantitatively and is found to exhibit an activation energy for migration of  ∼0.18 eV with a pre-exponential factor of  ∼[Formula: see text] cm² s^-1. The latter value evidences a simple jump process without any entropy effects for the motion of V ^2-. No deep level in the bandgap to be associated with V ^2- is observed but the results suggest that the level is situated deeper than  ∼0.19 eV below E _c , corroborating results reported previously in the literature.

Correction: Single-crystal TiO2 nanowires by seed assisted thermal oxidation of Ti foil: synthesis and photocatalytic properties

Correction for ‘Single-crystal TiO₂ nanowires by seed assisted thermal oxidation of Ti foil: synthesis and photocatalytic properties’ by E. Arcadipane et al., RSC Adv., 2016, 6, 55490–55498.

Ultra-doped n-type germanium thin films for sensing in the mid-infrared

A key milestone for the next generation of high-performance multifunctional microelectronic devices is the monolithic integration of high-mobility materials with Si technology. The use of Ge instead of Si as a basic material in nanoelectronics would need homogeneous p- and n-type doping with high carrier densities. Here we use ion implantation followed by rear side flash-lamp annealing (r-FLA) for the fabrication of heavily doped n-type Ge with high mobility. This approach, in contrast to conventional annealing procedures, leads to the full recrystallization of Ge films and high P activation. In this way single crystalline Ge thin films free of defects with maximum attained carrier concentrations of 2.20 ± 0.11 × 10(20) cm(-3) and carrier mobilities above 260 cm(2)/(V·s) were obtained. The obtained ultra-doped Ge films display a room-temperature plasma frequency above 1,850 cm(-1), which enables to exploit the plasmonic properties of Ge for sensing in the mid-infrared spectral range.

Single-crystal TiO2 nanowires by seed assisted thermal oxidation of Ti foil: synthesis and photocatalytic properties

TiO₂ nanowires growth was investigated varying the synthesis parameters. Nanowires demonstrated improved photocatalytic activity, especially when treated in forming gas.

Hydrogen induced optically-active defects in silicon photonic nanocavities

We demonstrate intense room temperature photoluminescence (PL) from optically active hydrogen- related defects incorporated into crystalline silicon. Hydrogen was incorporated into the device layer of a silicon on insulator (SOI) wafer by two methods: hydrogen plasma treatment and ion implantation. The room temperature PL spectra show two broad PL bands centered at 1300 and 1500 nm wavelengths: the first one relates to implanted defects while the other band mainly relates to the plasma treatment. Structural characterization reveals the presence of nanometric platelets and bubbles and we attribute different features of the emission spectrum to the presence of these different kind of defects. The emission is further enhanced by introducing defects into photonic crystal (PhC) nanocavities. Transmission electron microscopy analyses revealed that the isotropicity of plasma treatment causes the formation of a higher defects density around the whole cavity compared to the ion implantation technique, while ion implantation creates a lower density of defects embedded in the Si layer, resulting in a higher PL enhancement. These results further increase the understanding of the nature of optically active hydrogen defects and their relation with the observed photoluminescence, which will ultimately lead to the development of intense and tunable crystalline silicon light sources at room temperature.

Impurity sublattice localization in ZnO revealed by Li marker diffusion

Sublattice localization of impurities in compound semiconductors, e.g., ZnO, determines their electronic and optical action. Despite that the impurity position may be envisaged based on charge considerations, the actual localization is often unknown, limiting our understanding of the incorporation and possible doping mechanisms. In this study, we demonstrate that the preferential sublattice occupation for a number of impurities in ZnO can be revealed by monitoring Li diffusion. In particular, using ion implantation, the impurity incorporation into the Zn sublattice (holds for, B, Mg, P, Ag, Cd, and Sb) manifests in the formation of Li-depleted regions behind the implanted one, while Li pileups in the region of the implantation peaks for impurities residing on O sites, e.g., N. The behavior appears to be of general validity and the phenomena are explained in terms of the apparent surplus of Zn and O interstitials, related to the lattice localization of the impurities. Furthermore, Cd+O and Mg+O co-doping experiments revealed that implanted O atoms act as an efficient blocking "filter" for fast diffusing Zn interstitials.

Intrinsic point-defect balance in self-ion-implanted ZnO

The role of excess intrinsic atoms for residual point defect balance has been discriminated by implanting Zn or O ions into Li-containing ZnO and monitoring Li redistribution and electrical resistivity after postimplant anneals. Strongly Li-depleted regions were detected in the Zn-implanted samples at depths beyond the projected range (R(p)) upon annealing ≥ 600 °C, correlating with a resistivity decrease. In contrast, similar anneals of the O-implanted samples resulted in Li accumulation at R(p) and an increased resistivity. Control samples implanted with Ar or Ne ions, yielding similar defect production as for the Zn or O implants but with no surplus of intrinsic atoms, revealed no Li depletion. Thus, the depletion of Li shows evidence of excess Zn interstitials (Zn(I)) being released during annealing of the Zn-implanted samples. These Zn(I)'s convert substitutional Li atoms (Li(Zn)) into highly mobile interstitial ones leading to the strongly Li-depleted regions. In the O-implanted samples, the high resistivity provides evidence of stable O(I)-related acceptors.

Formation of donor and acceptor states of the divacancy-oxygen centre in p-type Cz-silicon

The formation of the divacancy-oxygen centre (V(2)O) in p-type Czochralski-grown silicon has been investigated by means of deep level transient spectroscopy (DLTS). The donor state (+/0) of V(2)O is located at ~E(v) + 0.23 eV (E(v) denotes the valence band edge) and emerges during heat treatment above 200 °C at the expense of the divacancy centre (V(2)). A concurrent transition takes place between the single-acceptor states of V(2) and V(2)O, as unveiled by the injection of electrons through optical excitation during the trap filling sequence of the DLTS measurements. Further, a defect with an energy level at ~E(v) + 0.09 eV evolves in close correlation with the growth of V(2)O but at a factor of ~5-6 lower in concentration. In the literature, the E(v) + 0.09 eV level has previously been attributed to a double-donor state of V(2)O but this assignment can be ruled out by the present data favouring a complex formed between migrating V(2) centres and a competing interstitial oxygen trap. In addition, a level at ~E(v) + 0.24 eV occurs also during the heat treatment above 200 °C and is tentatively assigned to the trivacancy-oxygen centre (V(3)O).

Self-directed relaxation in daily living

The purpose of this paper is to present a brief relaxation routine which can be easily learned and applied in daily living.