D.V. Davydov

Optical and Electrical Properties of 4H-SiC Irradiated with Fast Neutrons and High-Energy Heavy Ions

Photoluminescence and deep-level transient spectroscopy are used to study the effect of irradiation with fast neutrons and high-energy Kr (235 MeV) and Bi (710 MeV) ions on the optical and electrical properties of high-resistivity high-purity n-type 4H-SiC epitaxial layers grown by chemical vapor deposition. Electrical characteristics were studied using the barrier structures based on these epitaxial layers: Schottky barriers with Al and Cr contacts and p+-n-n+ diodes fabricated by Al ion implantation. According to the experimental data obtained, neutrons and high-energy ions give rise to the same defect-related centers. The results show that, even for the extremely high ionization density (34 keV/nm) characteristic of Bi ions, the formation of the defect structure in SiC single crystals is governed by energy losses of particles due to elastic collisions.

Effect of irradiation with fast neutrons on electrical characteristics of devices based on CVD 4H-SiC epitaxial layers

The effect of irradiation with 1-MeV neutrons on electrical properties of Al-based Schottky barriers and p+-n-n+ diodes doped by ion-implantation with Al was studied; the devices were formed on the basis of high-resistivity, pure 4H-SiC epitaxial layers possessing n-type conductivity and grown by vapor-transport epitaxy. The use of such structures made it possible to study the radiation defects in the epitaxial layer at temperatures as high as 700 K. Rectifying properties of the diode structures were no longer observed after irradiation of the samples with neutrons with a dose of 6×1014 cm−2; this effect is caused by high (up to 50 GΩ) resistance of the layer damaged by neutron radiation. However, the diode characteristics of irradiated p+-n-n+ structures were partially recovered after an annealing at 650 K.

Structural defects and deep-level centers in 4H-SiC epilayers grown by sublimational epitaxy in vacuum

The parameters of deep-level centers in lightly doped 4H-SiC epilayers grown by sublimational epitaxy and CVD were investigated. Two deep-level centers with activation energies Ec-0.18 eV and Ec-0.65 eV (Z1 center) were observed and tentatively identified with structural defects of the SiC crystal lattice. The Z1 center concentration is shown to fall with decreasing uncompensated donor concentration Nd-Na in the layers. For the same Nd-Na, the Z1 center concentration is lower in layers with a higher dislocation density.

Electrical and Optical Study of 4H-SiC CVD Epitaxial Layers Irradiated with Swift Heavy Ions

Radiation defects and electrical properties in 4H-SiC epitaxia l layer bombarded with 245 MeV Kr ions were studied using deep level transient spectroscopy (D LTS), photoluminescence and electrical measurements. Capacitance -, current and charge DLTS spectra have shown the presence mainly of Z1 (0.66 eV) deep level similar to those obtained f or electrons, neutrons and light ions. The temperature dependence of electrical resistivity of 4H-SiC structures with Schottky barriers was characterized by two stages that was connected w ith compound mechanism of the defects formation in SiC during heavy ions irradiation. Introduction Numerous experimental efforts aimed at study of radiation damage formation in SiC have been undertaken in the last few years. This activity concerns mainly w ith a structural, electrical and optical property changes in SiC exposed to high-level damage dose wit h electrons, neutrons and low-energy heavy ions. Substantially smaller attention was paid to effects of high-energy (hundred MeV) heavy ion irradiation in so-called electronic stopping power reg im , characterized with a large amount of energy deposition in electron subsystem of the cryst al lattice. At the same time, these effects are of interest due to promising application of the SiC based devices in space electronics and nuclear power set-up related to nuclear waste management. The first data obtained with high-energy ion beams have proved an excel lent radiation stability of SiC single crystals [1-3]. More compound mechanism of the influence of heavy Xe ions on SiC crystal lattice by comparison with electron and neutron irradiation was detected by positron annihilation spectroscopy [1]. Also a typical feature for a number of materials, associated with dense ionization effect – amorphous latent track formation, was not reg is e d by transmission electron microscopy even at huge electronic stopping power value 34 keV/nm [2]. The results of electrical property variations via in-situ registration of conducti vity of SiC under 5.5 GeV Xe ion irradiation and complemented with postradiation optical absorption measure ments were reported by Levalois et al. [3]. This paper, by our knowledge, is one only example of electrical characterization of SiC, irradiated with high-energy heavy ions and more detail and systematic studi es are required. In this work we apply different DLTS techniques, optical and electri cal measurements to study radiation defects in 4H-SiC epitaxial layers irradiated with 245 MeV Kr ions. Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 467-470 doi:10.4028/www.scientific.net/MSF.433-436.467

Electrical Study of Fast Neutron Irradiated Devices Based on 4H-SiC CVD Epitaxial Layers

The radiation-induced defect formation in high purity 4H-SiC CVD epitaxial layers and changes in the electrical properties of diode structures based on its after irradiation with different fluences ...

Investigation of the parameters of deep centers in n-6HSiC epitaxial layers obtained by gas-phase epitaxy

Epitaxial layers of 6H-SiC obtained by gas-phase epitaxy have been investigated by capacitance spectroscopy methods. It is shown that deep centers are present in the test samples. Such centers were previously observed in SiC epitaxial layers obtained by sublimation epitaxy. However, the total density of deep acceptors in structures prepared by gas-phase epitaxy is two to three orders of magnitude lower than in epitaxial films obtained by sublimation epitaxy with the same value of Nd-Na. It is suggested that the conditions of growth of the epitaxial layers influence the density and the type of defects formed in them.

Radiation Hardness of Silicon Carbide

The aim of this study was an estimation of the radiation hardness of silicon carbide and devices on its base. By using data, obtained by the authors, and literature data, it was possible to calculate carrier removal rate in SiC, irradiated by different charge participles, radiation defects (RD) introduction rate and generation constant of deeper RD. The obtained results were compared with known values of this parameters for Si. Results of comparison show, that during calculation of above parameters for SiC (or other wide-bandgap semiconductors (WBS), it is necessary to take into account their temperature dependence. Commonly, this comparison shows, that SiC is perspective material for developing radiation resistive devices, especially if they must work at high temperatures.

p-Type 6H-SiC Films in the Creation of Triode Structures for Low Ionization Radiation

The signal value of the transistor-like detector on applied voltage was investigated. It was measure induced-current recording from fluxes of X-ray and optical quanta. A superlinear rise in the resulting signal was observed with increasing voltage. The signal was amplified by a factor of several tens with respect to the value chosen for normalization. A description in terms of the phototriode model gives acceptable values for the main parameters: base width, diffusion length of electrons, and space charge region of the collector. It is important that SiC films with the thickness d similar to 10 mum can be used to detect penetrating radiation, for example, X-ray. The effective thickness of the films exceeds d by the signal amplification factor (and proves to be in range of hundred mum).

Origin and Behaviour of Deep Levels in Sublimation Growth of 4H-SiC Layers

The characteristics of boron incorporation and the resultant electrical behaviour have been studied for sublimation grown epilayers. Some factors which influence are the purity of the source material, growth temperature and growth time. The electrical activity of the shallow and deep level of boron has been investigated in relation to growth parameters and from the results the nature of the deep boron complex is discussed. The use of TaC coated graphite crucibles resulted in a decrease of the Z(1,2) concentration to less than low E13 cm(-3) which is the concentration obtained using graphite crucibles.