Papers by Author: Pavel L. Abramov

Abstract: A natural superlattice (NSL) in silicon carbide polytypes is shown to introduce a miniband structure into the conduction band, which leads to depressing of the electron impact zone-zone ionization at 300K with the electric field directed along the crystal axis or the NSL axis. The NSL influence can be also observed in the nitrogen impact ionization at 4.2K. In this case for the parallel field the impurity breakdown has not been fixed up to the fields 1.6 MV/cm in 6H-SiC. These results are explained by the insufficient gain in miniband for the ionization electron energy. Therewith the impurity breakdown at the electric field perpendicular to this axis correlates with a classical picture.

Abstract: It is demonstrated that polytype-homogeneous, thick (>100 m) epitaxial 3C-SiC layers of good quality with diameters of no less than 25 mm can be grown on 6H-SiC substrates by sublimation epitaxy in vacuum. These layers can be used as seeds for growing bulk 3C-SiC crystals by modified Lely method.

Abstract: Photoluminescence (PL) spectra of 3C-SiC(n,p)/6H-SiC(n) and 3C-SiC(p)/15R-SiC(n) heterostructures have been studied. A broad structureless band, absent in PL spectra of n–n heterostructures, was observed in the spectrum of p–n heterostructures in the energy range 2.2–2.4 eV. It is suggested that this band is due to the presence of a 2D electron gas in a quantum well near the heterointerface. High (~ 4000 cm2/s V) value of electron mobility and the absence of any significant fall in the mobility temperature dependence at liquid-nitrogen temperatures confirm the existence of a 2DEG in the QW at the heterointerface.

Abstract: In this work, we have studied I-V characteristics of Al breakdown in 6H-, 4H- and 15R-SiC in electrical field. As a result there obtained the next original data: 1) decreasing dependence of breakdown field due to the concentration increase in the range of Na – Nd = 5x1017–1019 cm-3; 2) absence of low temperature breakdown when Na - Nd< 1017 cm-3; 3) increasing of breakdown field while temperature declines from 77K to 4.2K; 4) at 300K the breakdown field decreases and the breakdown takes place in samples with the absence of low temperature breakdown; 5) gigantic enhancement of breakdown field at F||C. 6) the theoretical analysis based on the theory of a zero radius potential supports the probability of breakdown field enhancement at F||C.

Abstract: Photoelectric properties of 3C sublimation-grown epitaxial layers with different structural quality were studied by using time-resolved picosecond transient grating and free carrier absorption techniques. The layer quality was described by a parameter LTW which gives the total length of twin boundaries in a layer. Optical measurements of diffusion coefficients and carrier lifetimes in wide excess carrier density (N >1018 cm-3) and temperature range (10 K to 300 K) revealed the twin defect density dependent ambipolar mobility value at RT as well as essentially different temperature dependences of mobility of the layers. The larger value of absorption cross section in more defective layer at 1064 nm wavelength pointed out to contribution of defect-assisted absorption, which gradually vanished after the filling defect states by free carriers.

Abstract: n-type 3C-SiC films have been grown by sublimation epitaxy on hexagonal silicon carbide substrates. The low-temperature conductivity and magnetoresistance of the films have been studied in relation to their doping level and structural perfection. It was found that a metal--insulator transition occurs in the n-3C-SiC layer at concentrations Nd - Na ≤ 3 1017 cm-3.

Abstract: Highly doped p-3C-SiC layers of good crystal perfection have been grown by sublimation epitaxy in vacuum. Analysis of the photoluminescence (PL) spectra and temperature dependence of the carrier concentration shows that at least two types of acceptor centers at ~EV + 0.25 eV and at EV + 0.06-0.07 eV exist in the samples studied. A conclusion is made that layers of this kind can be used as p-emitters in 3C-SiC devices.

Abstract: 3C-SiC epitaxial layers were grown by method of sublimation epitaxy in vacuum on 6HSiC substrates. It was done investigation of magneto resistance and Hall effect of 3C-SiC/6H-SiC heterostructures in temperature range 1,4 – 300 К. At helium temperatures it was founded low samples resistance and negative magneto-resistance in week magnetic field ( ~ 1 T). Analysis of obtained results shows, that low samples resistance can be connected with metal-isolation junction in 3C-SiC epitaxial films..

Abstract: 3C-SiC epitaxial layers with a thickness of up to 100 μm and area of ~0.3-0.5 cm2 have been grown by sublimation epitaxy on hexagonal (6H-SiC) substrates at a maximum growth rate of about 200 μm per hour. The epilayers obtained are of n-type (Nd-Na ~ 1017 -1018 cm-3). According to X-ray data, the epitaxial layers are composed of the 3C-SiC polytype, without inclusions of other polytypes. The donor-acceptor (Al-N) recombination band with hνmax ~ 2.12 eV predominates in the photoluminescence (PL) spectrum. A detailed analysis of a PL spectrum measured at 6 K is presented. A conclusion is made that the epitaxial layers can be used as substrates for electronic devices based on 3C-SiC.