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Channeling of B and Al ions in 4H-SiC(0001), has been investigated by secondary ion mass spectrometry (SIMS). Ion implantations have been performed between room temperature (RT) and 600 °C at various fluences. Before implantation, the major crystal axes were determined and the sample was aligned using the blocking pattern of backscattered protons. As expected, the depth distribution of the implanted ions along a crystal direction penetrates much deeper compared to nonchanneling directions. At elevated temperatures, the channeling depth for 100 keV Al-ions is decreased due to lattice vibrations. For 50 keV B-ions, the temperature effect is minor, indicating a smaller interaction between target atoms and B. Simulations has been performed using SIIMPL, a Monte Carlo simulation code based on the binary collision approximation, to predict experimental data and get a deeper insight in the channeling process., QC 20191210

In this work, a complementary microstructural and optical approach is used to define processing conditions favorable for the formation of deep boron-related acceptor centers that may provide a pathway for achieving an intermediate band behavior in highly B-doped 3C-SiC. The crystallinity, boron solubility and precipitation mechanisms in sublimation-grown 3C-SiC crystals implanted to 1-3 at.% B concentrations were investigated by STEM. The revealed defect formation and boron precipitation trends upon thermal treatment in the range 1100-2000oC have been crosscorrelated with the optical characterization results provided by imaging PL spectroscopy. We discuss optical activity of the implanted B ions in terms of both shallow acceptors and deep D-centers, a complex formed by a boron atom and a carbon vacancy, and associate the observed spectral developments upon annealing with the strong temperature dependence of the D-center formation efficiency, which is further enhanced by the presence of implantation-induced defects. © 2018 Trans Tech Publications, Switzerland., Funding agencies:The authors gratefully acknowledge the financial support of this work by the Research Council of Norway (SunSiC Proj. No. 461224 22971), Swedish Energy Agency, Swedish Research Council (Proj. No. 621-2014-5825) and Swedish Governmental Agency for Innovation Systems (Vinnova).

The goal of this work is to investigate the morphology, electrical and optical properties of undoped ZnO (i-ZnO) thin layers deposited on Si substrates with (100) and (111) orientations. Plasma enhanced metalorganic chemical vapor deposition (PEMOCVD) was used for the deposition of i-ZnO layers at different temperatures. Atomic force microscopy (AFM), ellipsometry and four-probe method were used for the analysis. It is found that substrate orientation and growth temperature determine the morphological (grains size, surface roughness) as well as electrical properties of ZnO films. It is shown that the refractive index value depends on the surface morphology. It is concluded that properties of i-ZnO layers deposited on different Si substrates at different conditions exhibit some trends and peculiarities, which have to be taken into account for the processing of heterojunction solar cells by the PEMOCVD method. © 2007 Elsevier B.V. All rights reserved.

Defects in as-grown commercial zinc oxide (ZnO) substrates were studied by photoluminescence and optical detection of magnetic resonance (ODMR). In addition to the Zn vacancy and shallow donor centers, we observed several ODMR centers with spin S=1/2, labeled LU1-LU4. Among these, the axial LU3 and non-axial LU4 centers were detected in all studied samples. The ODMR signals of LU3/LU4 were found to be drastically increased after electron irradiation. The preliminary result indicates that these common ODMR centers in as-grown ZnO are related to intrinsic defects. © 2007 Elsevier B.V. All rights reserved., E-MRS Spring Meeting, 2007

Due to a constant increase in demands for transparent electronic devices the search for alternative transparent conducting oxides (TCO) is a major field of research now. New materials should be low-cost and have comparable or better optical and electrical characteristics in comparison to ITO. The use of n-type ZnO was proposed many years ago, but until now the best n-type dopant and its optimal concentration is still under discussion. Ga was proposed as the best dopant for ZnO due to similar atomic radius of Ga3+ compared to Zn2+ and its lower reactivity with oxygen. The resistivity ρ of ZnO:Ga/Si (100) films grown by PEMOCVD was found to be 3×10-2 Ω cm. Rapid thermal annealing (RTA) was applied to increase the conductivity of ZnO:Ga (1 wt%) films and the optimal regime was determined to be 800 {ring operator}C in oxygen media for 35 s. The resistivity ratio ρbefore / ρafter before and after the annealing and the corresponding surface morphologies were investigated. The resistivity reduction (ρbefore / ρafter ≈ 80) was observed after annealing at optimal regime and the final film resistivity was approximately ≈4×10-4 Ω cm, due to effective Ga dopant activation. The route mean square roughness (Rq) of the films was found to decrease with increasing annealing time and the grain size has been found to increase slightly for all annealed samples. These results allow us to prove that highly conductive ZnO films can be obtained by simple post-growth RTA in oxygen using only 1% of Ga precursor in the precursor mix. © 2007 Elsevier Ltd. All rights reserved.

Optical detection of magnetic resonance (ODMR) was used to study defects in ZnO substrates irradiated with 3 MeV electrons at room temperature. The Zn vacancy and some other ODMR centers were detected. Among these, the Zn vacancy and two other centers, labeled as LU3 and LU4, were also commonly observed in different types of as-grown ZnO substrates. The LU3 and LU4 are related to intrinsic defects and act as dominating recombination centers in irradiated and as-grown ZnO. © 2007 American Institute of Physics.

Optical detection of magnetic resonance (ODMR) was used to study defects in electron-irradiated ZnO substrates. In addition to the shallow donor and the Zn vacancy, several ODMR centers with an effective electron spin were detected. Among these, the axial LU3 and non-axial LU4 centers are shown to be dominating recombination centers. The annealing behavior of radiation-induced defects was studied and possible defect models are discussed.

The effect of ZnO buffer layers prepared at different temperatures on the structural, optical and morphological properties of the ZnO main layer is reported. ZnO thin films (comprising a buffer and a main layer) were deposited on (0 0 0 1) c-sapphire substrates by PEMOCVD. Two-step growth regimes were applied to realize a homoepitaxial growth on ZnO buffers: low-temperature ZnO buffer layer deposited at Ts=300 °C and the main layer at Ts=500 °C, high-temperature ZnO buffer layer deposited at Ts=500 °C and the main layer at Ts=300 °C. For comparison, a sample grown at high-temperature Ts=500 °C by one-step procedure was used. The low-temperature buffer layer has shown the most beneficial effect on the structural and morphological properties, as expressed by the narrowing of the (0 0 2) diffraction peak (FWHM=0.07°) and crystallite size enlargement. However, the surface roughness of this sample is higher then that of the sample grown by one-step procedure and this needs further considerations. The photoluminescence results seem to support a conclusion that the application of a low-temperature buffer layer among the studied temperature regimes is the most advantageous. © 2007 Elsevier B.V. All rights reserved.

A brief survey is given of some recent progress regarding ion implantation processing and related effects in 4H- and 6H-SiC. Four topics are discussed; an empirical ion range distribution simulator, dynamic defect annealing during implantation, formation of highly p(+)-doped layers, and deactivation of N donors by ion-induced defects., QC 20111003

Photoluminescence spectroscopy has been used to study single crystalline ZnO samples systematically annealed in inert, Zn-rich and O-rich atmospheres. A striking correlation is observed between the choice of annealing ambient and the position of the deep band emission (DBE) often detected in ZnO. In particular, annealing in O2 results in a DBE at 2.35±0.05 eV, whereas annealing in the presence of metallic Zn results in DBE at 2.53±0.05 eV. The authors attribute the former band to zinc vacancy (VZn) related defects and the latter to oxygen vacancy (VO) related defects. Additional confirmation for the VO and VZn peak identification comes from the observation that the effect is reversible when O- and Zn-rich annealing conditions are switched. After annealing in the presence of ZnO powder, there is no indication for the VZn- or VO-related bands, but the authors observe a low intensity yellow luminescence band peaking at 2.17 eV, probably related to Li, a common impurity in hydrothermally grown ZnO.

Zinc oxide (ZnO) is a promising semiconductor material with a great variety of applications, for example for highly conductive films for transparent electronics. Recently, Ga has been proposed as a dopant, exhibiting the advantages of a very similar atomic radius compared to Zn, a smaller reactivity, and a higher resistivity to oxidation compared to its competitor Al. In this study ZnO films, doped by Ga, were produced on Al2O3(0001) substrates by PEMOCVD. The doping was realized with 1, 3, 5 and 10 wt% gallium precursor content in the mixture. The resistivity of the prepared films, as well as the morphology and the transmittance, was investigated. All the deposited films have demonstrated a high optical transmittance above 93% in the range between 400 and 800 nm. A strong correlation between the electrical resistivity and the optical band gap depending on the Ga content was observed. An AFM analysis demonstrated highly uniform and smooth surfaces. The average grain size and route mean square roughness decreased with increasing Ga content. © 2005 Elsevier Ltd. All rights reserved.

Zinc oxide (ZnO) is a promising semiconductor material with a great variety of applications. Compared to undoped ZnO, impurity-doped ZnO has a lower resistivity and better stability. With this aim, Ga has been proposed as a dopant. In this study, the structural characteristics and surface morphology of ZnO films produced by PEMOCVD at a substrate temperature of 250 °C on the c-plane (001) of sapphire were investigated. Doping was realized with 1, 3, 5 and 10 wt.% of Ga2(AA)3 in the precursor's mixture. At lower contents, Ga stimulates growth of (002) oriented textured films and the smallest FWHM was obtained as low as 0.17° for ZnO:Ga with 1 wt.%. A change in preferential orientation as well as surface smoothing and roughness decreasing of the films were observed with further increasing Ga content in precursor's mixture. We assume a key role of Ga and note that such a feature would be beneficial for the application of ZnO thin films for formation of abrupt junctions in p-n device structures. © 2005 Elsevier B.V. All rights reserved.

The diffusion of boron in 4H-SiC has been studied by secondary ion mass spectrometry. Three kinds of epitaxial layers have been used, highly p-type, highly n-type and low doped n-type (intrinsic). A boron diffusion source has been introduced in the samples by ion implantation. Subsequent anneals have been carried out in Ar atmosphere in a RF-heated furnace between 1220degreesC and 2000degreesC for 5 min to 3 h. For the boron diffusion in the highly p-doped layer, 4x10(19) Al atoms/cm(3) an activation energy of 5.3 eV has been determined. A similar activation energy has been extracted in the highly n-doped layer, 1x10(19) N atoms/cm(3), although the absolute diffusivity values differ by four orders of magnitude. In the lightly n-doped layer, transient enhanced boron diffusion is observed at intrinsic conditions., QC 20111020

Implantation-induced excess vacancies and the related Cu gettering was studied in Si and in the solid solution Si0.93Ge0.07. The excess vacancy and interstitial generation during normal and inclined ion implantation can be simulated by a simple binary collision process. The excess defects are shown to control the Cu gettering observed in Si after rapid thermal annealing at a temperature of 900degreesC. The vacancy concentration in the SiGe layer is higher than in Si. An additional vacancy concentration of about 3.15x10(18)cm(-3) was determined in the SiGe layer beside the implantation-generated excess vacancies. These vacancies are presumably incorporated by the SiGe layer deposition on Si substrate. Vacancies agglomerate and form cavities during annealing. The cavities in SiGe were found to be significantly larger than in Si., QC 20111021

The study of self-diffusion of carbon (12C and 13C) in low-doped (intrinsic) 4H-SiC using secondary ion mass spectroscopy (SIMS) was presented. A two layer 13C enriched structure with 13C/12C ratios of 0.01 and 0.1, respectively, was prepared by using vapor phase epitaxy. The subsequent anneals were carried out in Ar atmosphere in a rf heated furnace between 2100 and 2350°C for 15 min-40 h. A small variation in the enriched 13C concentration and in the layer thickness over the wafer was also presented.

We have compared the electrical properties of n-type GaAs layers disordered by either 40 keV As ion implantation or an impurity-free process employing an SiO2 capping layer. Current–voltage and capacitance–voltage measurements on Au Schottky barrier diodes fabricated on the processed layers showed that the impurity-free method retained the much better electrical quality of the GaAs epitaxial layers. Different sets of defects were observed in the implanted samples and impurity free disordered samples, which meant that the charge transfer across the Schottky barriers was different in the two cases. Our results further reveal that the concentrations and diffusion lengths of defects created by ion implantation were much larger. The impurity-free method retains the better electrical quality of the semiconductor material.

The vacancy-dioxygen complex (VO2) is one of the main defects formed in irradiated Cz-Si crystals upon annealing (or irradiation) in the temperature range 300-400°C. In this defect two oxygen atoms share a vacancy, each bonded to two silicon neighbors. Independent vibrations of these O atoms give rise to one infrared absorption band at 895.5 cm-1 at 10 K. We report on an experimentally discovered bistability of this defect. We suggest an alternative configuration, VO2*, where only one O atom is inside the vacancy while the second O atom is in a backbond position. Two vibrational bands, at 928.4 and 1003.8 cm-1 (positions at 15 K), are assigned to this configuration. © 2003 Elsevier B.V. All rights reserved.

Infrared absorption studies of defect formation in Czochralski silicon irradiated with fast electrons in a wide range of temperatures (80-900 K) have been performed. The samples with different contents of oxygen (16O,18O) and carbon (12C,13C) isotopes were investigated. The main defect reactions are found to depend strongly on irradiation temperature and dose, as well as on impurity content and pre-history of the samples. Some new radiation-induced defects are revealed after irradiation at elevated temperatures as well as after a two-step (hot+room-temperature (RT)) irradiation. © 2002 Elsevier Science B.V. All rights reserved.

Ion implantation is an important technique for a successful implementation of commercial SiC devices. Much effort has also been devoted to optimising implantation and annealing parameters to improve the electrical device characteristics. However, there is a severe lack of understanding of the fundamental implantation process and the generation and annealing kinetics of point defects and defect complexes. Only very few of the most elementary intrinsic point defects have been unambiguously identified so far. To reach a deeper understanding of the basic mechanisms SiC samples have been implanted with a broad range of ions, energies, doses, etc., and the resulting defects and damage produced in the lattice have been studied with a multitude of characterisation techniques. In this contribution we will review some of the results generated recently and also try to indicate where more research is needed. In particular, deep level transient spectroscopy (DLTS) has been used to investigate point defects at very low doses and transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS) are used for studying the damage build-up at high doses. © 2002 Elsevier Science B.V. All rights reserved.

Interactions between the oxygen dimer (O2i) and silicon self-interstitials (I) and vacancies (V) have been studied in Czochralski-grown silicon (Cz-Si) crystals using infrared absorption and deep level transient spectroscopies. The focus in this report is on reactions of O2i with I. The first step in this interaction is found to be the formation of a self-interstitial-dioxygen centre (IO2i) with oxygen-related local vibrational mode (LVM) bands at 922 and 1037 cm-1. During the second formation step, another centre, I2O2i, with LVM bands at 918 and 1034 cm-1 is suggested to appear. A Si-related band at about 545 cm-1 is also assigned to both the IO2i and I2O2i centres. The IO2i centre is found to be electrically active with an acceptor level at Ec - 0.11 eV. The both defects, IO2i and I2O2i, are stable at room temperature and anneal out at about 400 and 550 K, respectively. © 2001 Elsevier Science B.V. All rights reserved.

Heavily Al-doped 4H-SiC structures have been prepared by vapor phase epitaxy. Subsequent anneals have been carried out in an Ar atmosphere in a rf-heated furnace between 1500°C and 2000°C for 0.5 to 3 h. Secondary ion mass spectrometry has been utilized to obtain Al concentration versus depth as well as lateral distributions (ion images). Transmission electron microscopy (TEM) has been employed to study the crystallinity and determine phase composition after heat treatment. A solubility limit of ~2 × 1020 Al/cm3 (1900°C) is extracted. Three-dimensional ion images show that the Al distribution does not remain homogeneous in layers heat treated at 1700°C or above when the Al concentration exceeds 2 × 1020 cm-3. Al-containing precipitates are identified by energy-filtered TEM. © 2001 American Institute of Physics.

Three vibrational infrared absorption bands at about 936, 944 and 956 cm-1 appear commonly in spectra of Czochralski-grown silicon irradiated at low temperatures. All three bands have earlier been assigned to local vibrational modes related to oxygen in the complex of the silicon and the oxygen interstitials (IOi). However, it is shown that such an assignment of the 936 cm-1 band clearly is inconsistent with many facts and observations and that the band is most likely due to oxygen vibrations in the Si interstitial pair and interstitial oxygen complex, I2Oi. © 2001 Published by Elsevier Science B.V.

UV-enhanced photodetectors of both n+-p and p+-n type have been processed in silicon. Photodetectors of the p+-n type display a responsivity close to the theoretical limit with an antireflective coating of either thermally grown dry silicon dioxide or deposited oxide (TEOS), followed by a short wet oxidizing step. This holds, irrespective of whether the detector window is doped by boron through ion implantation or diffusion from a solid source. However, for p+-n photodiodes with a TEOS-oxide in the as-deposited state the responsivity decreases substantially for wavelenghts below 500 nm compared to the theoretical predictions. This is attributed to a high recombination velocity at the silicon dioxide/silicon interface, as supported by computer simulations of the detector performance. In contrast, n+-p photodiodes are found to be rather insensitive with respect to the properties of the silicon dioxide/silicon interface. These results provide the first experimental demonstration that high built in electric fields, caused by abrupt dopant profiles, can suppress the influence of a high interface carrier recombination velocity., 1st International Workshop on Radiation Imaging Detectors; Sundsvall, Swed; 13 June 1999 through 16 June 1999