M. G. Rastegaeva

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.

Surface barrier height in metal-n-6H-SiC structures

Abstract This work makes a comparison of some experimental data on surface barrier height with calculations based on classical models of surface barrier formation in semiconductor-metal structures. We have estimated the dependences of surface barrier height on surface states density, the value of Fermi level surface “pinning”, metal workfunction and uncompensated donors concentration. These calculations together with available experimental data made it possible to estimate surface properties of real 6H-SiC-metal structures.

Allowing for current spreading in semiconductors during measurements of the contact resistivity of ohmic contacts

A modification of the contact-area pattern with radial geometry, which has certain advantages in determining the contact resistivity of ohmic contacts (ρc) fabricated on substrates and low-resistance semiconductor layers, is proposed. Different variants of its application for both the transmission line method (TLM) and methods based on a numerical calculation of the resistance of the semiconductor with allowance for current spreading are considered. It is shown that the transmission line method makes it possible to obtain an upper estimate of the contact resistivity on substrates. The errors of such estimates are also calculated as a function of the parameters of the semiconductor and the contact. The TLM estimate is a good first approximation for determining the exact value of ρc by numerically calculating the resistance of the semiconductor. The results obtained are used to study the contact resistivity of Ni-based ohmic contacts on n-6H-SiC substrates.

Temperature dependence of the threshold current of QW lasers

The temperature dependence of the threshold current in GaInAs-based laser structures has been studied in a wide temperature range (4.2 ≤ T ≤ 290 K). It is shown that this dependence is monotonic in the entire temperature interval studied. Theoretical expressions for the threshold carrier density are derived and it is demonstrated that this density depends on temperature linearly. It is shown that the main contribution to the threshold current comes from monomolecular (Shockley-Read) recombination at low temperatures. At T > 77 K, the threshold current is determined by radiative recombination. At higher temperatures, close to room temperature, Auger recombination also makes a contribution. The threshold current grows with temperature linearly in the case of radiative recombination and in accordance with T3 in the case of Auger recombination.

High-efficiency (49%) and high-power photovoltaic cells based on gallium antimonide

High-efficiency GaSb-based photovoltaic cells designed for conversion of high-power laser radiation and infrared radiation of emitters heated by concentrated solar radiation are fabricated and studied. The maximum efficiency of conversion of the radiation with λ = 1680 nm was 49% at the photocurrent density of 50–100 A/cm2 for the fabricated photovoltaic cells. The methods for reducing the losses at ohmic contacts to p-and n-GaSb are investigated. The minimum values of the specific resistance, (1–3) × 10−6 Θ cm2, of contact to p-GaSb with the doping level of 1020 cm−3 were obtained using the Ti/Pt/Au contact system. The minimum values of the specific contact resistance were (1–3) × 10−6 Θ cm2 in the case of n-GaSb with the doping level of 2 × 1018 cm−3 if the Au(Ge)/Ni/Au and Au/Ni/Au contact systems are used.

Thermal delocalization of carriers in semiconductor lasers (λ = 1010–1070 nm)

The temperature dependences of the emission characteristics of semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures (wavelengths λ = 1010–1070 nm) have been studied. It was found that, in the continuous-wave mode, the main mechanism of “saturation” of the light-current characteristic with increasing temperature of the active region is carrier delocalization into the waveguide layer. It was experimentally demonstrated that the thermal delocalization of carriers depends on the energy depth of the quantum well (QW) in the active region. It is shown that the minimum internal optical loss at 140°C is obtained in laser structures with the largest energy depth of the QW of the active region.

A decrease in ohmic losses and an increase in power in GaSb photovoltaic converters

The transmission-line model with radial and rectangular geometry of contact pads has been used to study the contact systems Cr-Au, Cr-Au-Ag-Au, Ti-Pt-Au, Pt-Ti-Pt-Au, Pt-Au, Ti-Au, Ti-Pt-Ag, Ti-Pt-Ag-Au, and Pt-Ag deposited on the p-GaSb surface by the methods of magnetron sputtering and resistive evaporation. It is established that the contact systems Ti-Pt-Ag-Au and Ti-Pt-Ag exhibit the smallest values of the specific contact resistance (ρc ≤ 10−6 Ω cm2), which makes it possible to use these systems in fabrication of photovoltaic converters generating photocurrents with densities as high as 15 A/cm2.

Surface barrier height in metal-SiC structures of 6H, 4H and 3C polytypes

Abstract We have studied metal-silicon carbide barrier height for various structures. Material of both n- and p-type conductivity 3C, 6H and 4H varieties have been used with Mo or Au Schottky barriers. In some cases, we observe a dependence of the barrier height on the uncompensated impurity concentration which cannot be explained in terms of the simple image force barrier lowering. It demands to take into account the total charge balance at the metal-semiconductor interface. The analysis of these data, together with other data on the surface barrier height, gives useful information for the development of high temperature devices.

Perspectives of Use of Diagnostic Mirrors with Transparent Protection Layer in Burning Plasma Experiments

We evaluate using of metal mirrors over‐coated with transparent protection layer for the in‐vessel diagnostic systems in reactor‐grade fusion devices. Ideally, these should satisfy the contradictory demands of high reflectivity and small rate degradation when being bombarded by CX atoms. The serious threat to the performance of diagnostic mirrors is surface contamination with carbon‐based material eroded from carbon tiles. Via coupling the protective layer to a bulk mirror we can mitigate the deposit infiuence on the reflectance spectra. The regards are given to survivability in plasma environment of protected coated metallic mirrors.

850-nm diode lasers with different ways of compensating for internal mechanical stresses in an AlGaAs:P/GaAs heterostructure

MOS hydride epitaxy is used to grow AlGaAs/GaAs heterostructures both without compensation and with compensation for internal mechanical stresses by the introduction of phosphorus into different layers of the heterostructure; this compensation affects the lattice parameter of the layer and, thus, influences the value of internal stresses in the entire laser hetetrostructure. Multimode mesastripe laser diodes (with an aperture of 100 μm) emitting at a wavelength of 850 nm are fabricated on the basis of the above structures; the properties of these diodes are studied. It is shown that the structures with compensated internal mechanical stresses exhibit a linear power-current characteristic if the pump currents do not exceed those corresponding to the maximum of the output power. Such structures with compensated internal mechanical stresses exhibit larger values for the characteristic temperatures T0 and T1 in comparison with structures with uncompensated internal mechanical stresses.