Anatoly M. Strel'chuk

Fabrication of SiC epitaxial structures for devices by the method of sublimation in an open system

Abstract The growth conditions of 6H-SiC epitaxial layers by an open sublimation method have been studied. Diodes, field effect transistors, UV photodiodes and Schottky barrier diodes are demonstrated.

Influence of proton irradiation on recombination current in 6H–SiC pn structures

Abstract The effect of proton bombardment on recombination current and the value of the steady state lifetime of nonequilibrium carriers for 6H–SiC pn structures created by sublimation epitaxy was investigated. The irradiation was carried out with 8-MeV protons in the range of doses from 10 14 –10 16 cm −2 . Irradiation with a dose of 3.6×10 14 cm −2 increases the recombination current and decreases the steady-state lifetime for deep-level recombination in the space charge region by up to two orders of magnitude. Irradiation with higher doses (up to 5×10 15 cm −2 ) or annealing at temperatures in the range 300–800 K leaves the recombination current and steady state lifetime practically unchanged.

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.

Influence of Gamma-Ray and Neutron Irradiation on Injection Characteristics of 4H-SiC pn Structures

The effect of gamma-ray and neutron irradiation on recombination current, injection electroluminescense and the value of the lifetime of nonequilibrium carriers for 4H-SiC pn structures was investigated. The irradiation was carried out with gamma-ray (dose 5x106 rad) and 1 MeV neutrons in the doses range from 1.2x1014 cm-2 to 6.24x1014 cm-2. Neutron irradiation with a dose 1.2x1014 cm-2 increased the recombination current, decreased the lifetime for deep-level recombination in the space charge region and decreased the intensity of the edge injection electroluminescense (hnmax » 3.16 eV) by 1.5-2 orders of magnitude; the neutron irradiation with high dose (6.24x1014 cm-2) resulted in increase of the recombination current up to 2 orders of magnitude and decrease of lifetime at least up to 2 orders of magnitude. Gamma-ray irradiation and annealing at temperatures in the range 350-650 K left the recombination current and lifetime practically unchanged.

Characterization of p-n structures grown by sublimation heteroepitaxy of 3C-SiC on 6H-SiC

Abstract A study on forward I – V characteristics of p–n structures grown by sublimation heteroepitaxy of 3C-SiC on 6H-SiC shows that about 90% of all the diodes can be placed in two groups. Current–voltage ( I – V ) characteristics of type I diodes are close to those of high-perfection p–n homostructures based on bulk 3C-SiC, with some indications of tunneling currents. I – V characteristics of type II diodes are close to those of p–n homostructures grown by epitaxial methods on single-crystal 6H-SiC substrates. Diodes of both types emit in the entire visible spectral range. The longer-wavelength emission is predominant in type I diodes, and shorter-wavelength emission in type II diodes. However, the main feature of the injection electroluminescence (IEL) is the qualitative similarity of the IEL spectra for diodes of both types. In particular, the IEL spectra of both diode types contain two bands (with hν max ≈2.3 and 2.9 eV), attributed to free exciton annihilation in 3C-SiC and 6H-SiC, respectively.

Characterization of 3C-SiC/6H-SiC Heterostructures Grown by Vacuum Sublimation

In I-V, EL characterization it was concluded that during the growt h on n-type 6H-SiC substrate of 3C-SiC layer the not intentionally doped regions of p-t ype conductivity formed. It thus appears that two types of pn structures are being formed identifi ed by the polarity of voltage applied to Ni contact on the surface of the epitaxial layer and di splaying different spectra of injection EL. In the EL spectra of the first structure type a peak at h νmax= 2.3 eV is present which, similar to the peak due to free exciton annihilation in 3C-SiC. In the EL spectra of the second structure type two peaks are observed of the same origin as the peaks identified in 6H-SiC pn structures and one more, longer wavelength peak at h νmax between 2.35 and 2.5 eV. TEM revolved that the intermediate layer belongs to 6H polytype. According to EBIC characterization the intermediate layer in studied sample was p-type conductivity. Introduction. Cubic silicon carbide (3C-SiC) is at present a topic of considera ble interest for semiconductor electronics due to the highest charge mobility among all SiC poly types. At certain conditions a growth of α-SiC epilayers on basal orientated substrates of 6H-SiC is a ccompanied by growth of islands of 3C-SiC or transformation of the whole 6H-SiC epilayer into 3C-SiC epilayer. Deposition of 3C layer corresponds to the island growth resulting in double positi on boundaries (DPBs) and stacking fault (SF) formation. Modifying growth conditions in the grow th zone it is possible to obtain various density of DPBs and SF. In recent years, considerable progress has been achieved in the sublimation epitaxy technology. High-quality epitaxial structures of the (n)3C-SiC-(n)6H-SiC type with low densities of DPBs and SF were obtained [1]. The area of n-3C-SiC twin was up to 25 mm. Electrical characteristics of the pn structures were close to those of high perfection pn homostructures based on bulk 3C-SiC [2]. Within the framework of this paper the questions to be discussed will be concerned with epilayer having high density of DPB’s to understand the connection of this defect with electrical characteristics of the structure. Experimental. Epitaxial 3C-SiC layer was grown on 6H-SiC substrate by typical for n-type epitaxy sublimation process in vacuum. Very high density of DPB’s was confirmed by X-ray topography (Fig.1, see also [3]). After that a Ni film was deposited by magnetron sputtering on the surface of the epitaxial layer at 300 C. Ni spots 100microns in diameter were formed by photolitography. Backside ohmic contact (to the Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 293-296 doi:10.4028/www.scientific.net/MSF.433-436.293

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

6H(n+)/3C(n)/6H(p+) - SiC Structures Grown by Sublimation Epitaxy

Investigation of the multilayer 6H(n+)/3C(n)/6H(p+)-SiC heterostructure grown by sublimation epitaxy show that the injection electroluminescence (IEL) in the green region (hνmax≈2.30-2.35eV) of spectrum is dominant. This band is close to the electroluminescence peak due to defects in 6H-SiC but also can be due to free exciton annihilation in a quantum well in 3C-SiC at the 6H/3C-SiC heterointerface. At high current the IEL peak at hνmax≈2.9 eV is found. This peak (and also two another peaks in blue part of spectra: hνmax≈2.6 eV and hνmax≈2.72 eV) can be attributed to recombination in 6H-SiC. The forward current-voltage characteristics for best structures are close to those for ideal 6H-SiC pn homostructure and characterized by abrupt breakdown. A lot of structures are characterized by barrier type excess current. Structure in the region of evident 3C-SiC inclusion is characterized by high forward and reverse excess currents.

Influence of Irradiation on Excess Currents in SiC pn Structures

Excess currents of the different nature in 6H-SiC pn structures of the different origin and parameters were investigated. The effect of the suppression of the forward and reverse excess currents were observed after 0.9 MeV electron (dose 5x1016 ÷ 1.6x1017 cm-2) and 8 MeV proton (dose 5x1015 cm-2) irradiation for structures with shunts which is probably due to the presence of relatively small inhomogeneities. The shunts in another group of pn structures probably are more high capability and they are more stable against degradation during irradiation.

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 ...