Radiation defects in n-4H-SiC irradiated with 8-MeV protons

Capacitance-related methods and electron spin resonance were used to study the deep-level centers formed in n-4H-SiC as a result of irradiation with 8-MeV protons. For the samples, Schottky diodes and p-n structures formed on the layers either obtained by sublimational epitaxy or produced commercially by CREE Inc. (United States) were used. It was found that the type of centers introduced by irradiation is independent of the technology of the material growth and the type of charged particles. On the basis of the results of annealing the defects and the data of electron spin resonance, the possible structure of the centers is suggested.     

Electron spin resonance study of defects in CVD-grown 3C-SiC irradiated with 2MeV protons

Electron spin resonance (ESR) was used to study defects induced by 2MeV-proton irradiation in cubic silicon carbide (3C-SiC) epitaxially grown on Si substrates by chemical vapor deposition. A new ESR signal labeled T5 was observed at temperatures lower than ≈100 K in Al doped, p-type 3C-SiC epilayers irradiated. The T5 signal has anisotropic g-values of g₁ = 2.0020 ± 0.0001, g₂ = 2.0007 ± 0.0001,and g₃ = 1.9951 ± 0.0001. The principal axes of the g-tensor were found to be along the 〈100〉 directions, indicating that the T5 center has D₂ symmetry. Isochronal annealing of the irradiated epilayers showed that the T5 center was annealed at temperatures around 150° C. A tentative model is discussed for the T5 center.     

Radiation resistance of transistor-and diode-type SiC detectors irradiated with 8-MeV protons

Nuclear-particle detectors based on SiC with a structure composed of an n⁺-type substrate, a p-type epitaxial layer, and a Schottky barrier are studied. Structures with a ～10-µm-thick 6H-SiC layer exhibit transistor properties, whereas those with a ～30-µm-thick 4H-SiC layer exhibit diode properties. It is established that a more than tenfold amplification of the signal is observed in the transistor-type structure. The amplification is retained after irradiation with 8-MeV protons with a dose of at least 5×10¹³ cm^?2; in this case, the resolution is ≤10%. Amplification of the signal was not observed in the structures of diode type. However, there were diode-type detectors with a resolution of ≈3%, which is acceptable for a number of applications, even after irradiation with the highest dose of 2×10¹⁴ cm^?2.     

Hydrogen passivation in n- and p-type 6H-SiC

Hydrogen passivation effects are found to be much more prevalent in p-type 6H-SiC relative to n-type material. Reactivation of passivated B acceptors occurs at ~700°C, corresponding to a reactivation energy of ~3.3 eV. This is much higher than for passivated acceptors in Si, where reactivation occurs at ≤200°C. The incorporation depth of ²H from a plasma at 200°C is ≤0.1 μm in 30 min, corresponding to a diffusivity approximately two orders of magnitude lower than in Si at the same temperature. The average energy of ions in the ²H plasma has an influence on the peak concentration of incorporated deuterium and on its diffusion depth.     

Hydrogen interaction with defects and impurities in 6H-SiC

The dynamics of hydrogen capture and release from trapping centers in 6H-SiC after plasma hydrogenation and annealing was investigated by low-temperature photoluminescence (PL). Indications of competing processes of hydrogen capture by different trapping centers were observed. Passivation of Al acceptors with hydrogen is the dominating process during plasma hydrogenation or plasma etching. Irreversible release of hydrogen from Al-trapping centers and additional trapping of hydrogen by Si vacancy (V_Si) to form a V_Si+H complex occurred during annealing at temperatures above 300°C. It is suggested that the V_Si+H complex may be playing an important role in keeping hydrogen in SiC after higher temperature treatment.     

Some challenging points in the identification of defects in floating-zone <Emphasis Type="Italic">n</Emphasis>-type silicon irradiated with 8 and 15 MeV protons

Electrical properties of defects formed in n-Si(FZ) following 8 and 15 MeV proton irradiation are investigated by Hall effect measurements over the wide temperature range of T ≈ 25 to 300 K. Close attention is paid to the damaging factor of proton irradiation, leaving aside passivation effects by hydrogen. The concept of defect production and annealing processes being accepted in the literature so far needs to be reconsidered. Contrary to expectations the dominant impurity-related defects produced by MeV protons turn out to be electrically neutral in n-type material. Surprisingly, radiation acceptors appear to play a minor role. Annealing studies of irradiated samples of such complex defects as a divacancy tied to a phosphorus atom and a vacancy tied to two phosphorus atoms. The latter defect features high thermal stability. Identification of the dominant neutral donors, however, remains unclear and will require further, more detailed, studies. The electric properties of the material after proton irradiation can be completely restored at T = 800°C.     

Effective recombination levels in n- and p-type silicon irradiated by 4·5 MeV electrons

The effective recombination levels created at room temperature by 4·5 MeV electron irradiation are deduced from the variations in lifetime vs carrier injection rate, electron fluence, and temperature. This paper aims to compare the properties of the created recombination energy levels and defect centers in N- and P-type silicon single crystals. The characteristics of the samples used extend over a wide range of resistivities, doping impurities and crystal growth techniques. A pulsed neodymium laser has been employed to carry out these studies, and the carrier lifetime has been measured by the photoconductivity-decay method. Information on the specific centers is deduced from the comparison of the present macroscopic results on energy levels and annealing studies with the known properties of microscopic defects.From the results obtained, several types of recombination centers are simultaneously created in N- and P-type silicon, and crystal impurities other than oxygen and dopants may play a big part in the constitution of such centers. In the P-type silicon case, 3 types of recombination centers are clearly operative: (1) centers with a ～E_v+0·20 eV energy level, which could be divacancies, and which would cease to act as recombination centers by trapping irradiation induced interstitial carbon atoms, (2) centers with a ～E_v+0·24 eV level which may involve aluminium interstitial atoms, and finally (3) centers with a ～E_v+0·27 eV level, which are K centres. These recombination centers are more or less active, depending on the initial characteristics of the sample. In the N-type silicon case, only two groups of effective recombination levels, ～E_c?0·17 and E_v+0·3 eV, appear in the irradiated materials. However, the effects of centers possibly linked to the presence of contaminants, such as carbon and aluminium, must be added to the known effects of the divacancy, doping atom-vacancy and oxygen-vacancy complexes to explain the carrier lifetime degradation and recovery.     

Comparison of current-voltage characteristics of n- and p-type 6H-SiC Schottky diodes

Current-voltage (I–V) characteristics of n- and p-type 6H−SiC Schottky diodes are compared in a temperature range of room temperature to 400°C. While the room temperature I–V characteristics of the n-type Schottky diode after turn-on is more or less linear up to ∼100 A/cm², the I–V characteristics of the p-type Schottky diode shows a non-linear behavior even after turn-on, indicating a variation in the on-state resistance with increase in forward current. For the first time it is shown that at high current densities (>125 A/cm²) the forward voltage drop across p-type Schottky diodes is lower than that across n-type Schottky diodes on 6H−SiC. High temperature measurements indicate that while the on-state resistance of n-type Schottky diodes increases with increase in temperature, the on-state resistance of p-type Schottky diodes decreases with increase in temperature up to ∼330 K.     

Electrical properties of InAs irradiated with protons

The results of studying the electrical properties of InAs irradiated with 5-MeV H⁺ ions at a dose of 2×10¹⁶ cm^?2 are reported. It is shown that, independently of the doping level and the conductivity type of the as-grown InAs, InAs always has the n⁺-type conductivity after irradiation (n≈(2–3)×10¹⁸ cm^?3). The phenomenon of pinning of the Fermi level in the irradiated material is discussed. The thermal stability of radiation damage in InAs subjected to postirradiation annealing at temperatures as high as 800°C was studied.     

Photocurrent amplification in Au/SiO2/n-6H-SiC MOS structures with a tunnel-thin insulator

The first observation of amplification of the photogeneration current in Au/SiO₂/n-6H-SiC structures with a tunnel-thin insulator is reported. This effect can be used to increase the efficiency of existing UV-range 6H-SiC-based photodiodes. It also shows that bipolar SiC transistors with a MOS tunnel emitter can be produced. Fiz. Tekh. Poluprovodn. 32, 1145–1148 (September 1998)     

An EPR study of defects induced in 6H-SiC by ion implantation

Crystalline (0001) plane wafers of n-type 6H-SiC have been implanted at room temperature with 200 keV Ge⁺ ions in the dose range 10¹² to 10¹⁵ cm⁻². Electron paramagnetic resonance (EPR) measurements have been made on these samples both before and after annealing them at temperatures in the range room temperature to 1500°C. The as-implanted samples have a single isotropic and asymmetric line EPR spectrum whose width, ΔB_pp, increases with ion dose before falling when a buried continuous amorphous layer is produced. This increase is interpreted in terms of the change in the relative intensity of a line with g = 2.0028 ± 0.0002, ΔB_pp = 0.4 mT associated primarily with carbon dangling bonds in a-SiC and a line with g in the range 2.0033 to 2.0039 of uncertain origin. The variation with anneal temperature of the populations of these defects is reported.     

Radiation degradation characteristics of component subcells in inverted metamorphic triple‐junction solar cells irradiated with electrons and protons

The radiation response of In_0.5Ga_0.5P, GaAs, In_0.2Ga_0.8As, and In_0.3Ga_0.7As single‐junction solar cells, whose materials are also used as component subcells of inverted metamorphic triple‐junction (IMM3J) solar cells, was investigated. All four types of cells were prepared using a simple device layout and irradiated with high‐energy electrons and protons. The essential solar cell characteristics, namely, light‐illuminated current–voltage (LIV), dark current–voltage (DIV), external quantum efficiency (EQE), and two‐dimensional photoluminescence (2D‐PL) imaging were obtained before and after irradiation, and the corresponding changes due to the irradiations were compared and analyzed. The degradation of the cell output parameters by electrons and protons were plotted as a function of the displacement damage dose. It was found that the radiation resistance of the two InGaAs cells is approximately equivalent to that of the InGaP and GaAs cells from the materials standpoint, which is a result of different initial material qualities. However, the InGaAs cells show relatively low radiation resistance to electrons especially for the short‐circuit current (I sc). By comparing the degradation of I sc and EQE, data, It was confirmed that the greater decrease of minority‐carrier diffusion length in InGaAs compared with InGaP and GaAs causes severe degradation in the photo‐generation current of the InGaAs bottom subcells in IMM3J structures. Additionally, it was found that the InGaP and two InGaAs cells exhibited equivalent radiation resistance of V oc, but radiation response mechanisms of V oc are thought to be different. Further analytical studies are necessary to interpret the observed radiation response of the cells. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.     

Planar defects in 4H-SiC PiN diodes

Using plan-view transmission electron microscopy (PVTEM), we have identified stacking faults (SFs) and planar defects in 4H-SiC PiN diodes subjected to electrical bias. Our observations suggest that not all planar defects seen in the PiN diodes are SFs. By performing diffraction-contrast imaging experiments using TEM, we can distinguish SFs from other planar defects. In addition, high-resolution TEM (HRTEM) imaging and analytical TEM have revealed that some planar defects consist of a 3-nm-wide SiC amorphous layer. Many of these planar defects are orientated parallel to {1 00} planes, whereas others are roughly parallel to the (0001) plane. The appearance of these planar defects suggests that they are grain boundaries.     

Isochronous annealing of n-Si samples irradiated with 25-MeV protons

The Hall effect in proton-irradiated n-Si single crystals with the initial concentration of conduction electrons N = 6 × 10¹³ cm^?3 is studied experimentally. It is shown that, upon irradiation of the crystals with 25-MeV protons, the electron mobility anomalously increases. This increase is caused by the formation of metal inclusions in the crystals with ohmic junctions at the interfaces between the inclusions and semiconductor matrix. During isochronous annealing, shells nontransparent for conduction electrons made of negatively charged acceptor-type radiation defects are formed, resulting in a sharp decrease in the mobility. The oscillatory dependence of the mobility on the annealing temperature is attributed to variations in the degree of the screening of metal inclusions with negatively charged shells. The aggregates of interstitial atoms (metal inclusions) are annealed at 400°C.     

Optical and electrical properties of 4H-SiC irradiated with Xe ions

Structures with aluminum-ion-implanted p ⁺-n junctions formed in 26-μm-thick chemicalvapor-deposited-epitaxial 4H-SiC layers with an uncompensated donor concentration N _d ?N _a = (1–3) × 10¹⁵ cm^?3 are irradiated with 167-MeV Xe ions at fluences of 4 × 10⁹ to 1 × 10¹¹ cm^?2 and temperatures of 25 and 500°C. Then as-grown and irradiated structures are thermally annealed at a temperature of 500°C for 30 min. The as-grown, irradiated, and annealed samples are analyzed by means of cathodoluminescence, including the cross-sectional local cathodoluminescence technique, and electrical methods. According to the experimental data, radiation defects penetrate to a depth in excess of several tens of times the range of Xe ions. Irradiation of the structures at 500°C is accompanied by “dynamic annealing” of some low-temperature radiation defects, which increases the radiation resource of 4H-SiC devices operating at elevated temperatures.     

Deep levels in the band gap of GaN layers irradiated with protons

Deep-level transient spectroscopy was used to study the parameters of deep levels in the band gap of epitaxial n-GaN layers after irradiaton of the Schottky barriers with 1-MeV protons to a dose of 10¹² cm^?2. A deep level EP1 with an activation energy of 0.085 eV was introduced by irradiation into the upper half of the GaN band gap. The introduction rate of the corresponding defect was found to depend on the bias voltage applied to the Schottky barrier during irradiation.     

Conductivity compensation in n-4H-SiC (CVD) under irradiation with 0.9-MeV electrons

The effect of electron irradiation on n-4H-SiC is studied by the methods of capacitance-voltage characteristics and photoluminescence. The carrier-removal rate is found to be V _d ≈ 0.25 cm^?1. Total conductivity compensation in samples with an initial carrier concentration of (1–2) × 10¹⁵ cm^?2 is observed at irradiation doses of ～5 × 10¹⁵ cm^?2. Simultaneously with an increase in the compensation, a rise in the intensity of defect-related luminescence characteristic of 4H-SiC is observed. The sample parameters before irradiation and after irradiation and annealing are compared. The physical mechanisms of compensation in the samples under study are analyzed.     

Low-Temperature Annealing of Lightly Doped n-4H-SiC Layers after Irradiation with Fast Electrons

Semiconductors - The effect of low-temperature (up to 600°C) isothermal and isochronous annealing on the electrical characteristics of irradiated n-4H-SiC JBS Schottky diodes is studied....     

Al掺杂6H-SiC铁磁性研究(英文)

使用物理气象沉积法生长了轻Al掺杂6H-SiC样品,并使用超导量子干涉磁强计(SQUID)对无腐蚀及腐蚀后的样品进行了测试,发现了腐蚀后的样品在室温下表现出铁磁性。经过计算,样品磁信号并非来源于腐蚀剂KOH及K2CO3。同时腐蚀后的样品形貌表明杂质聚集在腐蚀后的缺陷附近从而形成了一定的铁磁性,因此缺陷被腐蚀放大是样品形成铁磁性的主要原因。     

Electrical properties and limiting position of the fermi level in InSb irradiated with protons

The results of experimental and simulation studies of electrical parameters and the limiting position of the Fermi level in metallurgically and transmutationally doped InSb irradiated with protons (10 MeV, 2×10¹⁶ cm^?2, 300 K) are reported. It is shown that the limiting electrical parameters of irradiated InSb correspond to a p-type material. Special features of the annealing of radiation defects are studied in the temperature range 20–500°C.