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Ti/Al/Ni/Au metallization widely used in the technology of GaN base devices have a very important imperfection i.e. rough surface. There are different opinions about the causes of this imperfection: balling-up of molten aluminum or the appearance of intermetallic melt phases in the Au–Al system. To check the effect of the former cause, we have studied the formation of rough surface after annealing of Ti/Al metallization which is used as a basis of many metallization systems for GaN. The substrates were made from silicon wafers covered with Si3N4 films (0.15 μm). On these substrates we deposited the Ti(12 nm)/Al(135 nm) metallization system. After the deposition the substrates were annealed in nitrogen for 30 s at 850 °С. The as-annealed specimens were tested for metallization sheet resistivity, appearance and surface morphology. We have shown that during annealing of the Ti/Al metallization system, mutual diffusion of the metals and their active interaction with the formation of intermetallic phases occur. This makes the metallization system more resistant to subsequent annealing, oxidation and chemical etching. After annealing the surface of the Ti/Al metallization system becomes gently matted. However, large hemispherical convex areas (as in the Ti/Al/Ni/Au metallization system) do not form. Thus, the hypothesis on the balling-up of molten aluminum on the surface of the Ti/Al metallization system has not been confirmed.

The Ti/Al/Ni/Au multilayer metallization system is widespread in the technology of n-GaN-based devices. Herein, the mechanisms of the formation of the surface roughness of the Ti/Al/Ni/Au metallization (with 300 nm hillocks) upon annealing in a nitrogen atmosphere for 30 s at a temperature of 850°C, which creates problems in further lithographic processes, and the ways of overcoming this disadvantage have been studied. The formation of a rough surface during the annealing of a multilayer metallization, associated with the interaction of the constituent metals, has been investigated with the Ti/Al/Ni and Ti/Al/Ni/Au systems. An increase in the sheet resistance of both metallization systems as the annealing temperature is raised can be explained by the interdiffusion of metals and the growing degree of interaction between them with the formation of various intermetallic compounds, exhibiting a far higher specific resistance than that of the initial metals. The X-ray analysis has confirmed the origination of the main NiTi, Al3Ti, and Ni2Al3 intermetallic phases in the Ti/Al/Ni three-layer metallization upon annealing. The surface of the Ti/Al/Ni metallization system has become rougher upon annealing; however, large hemispherical convexes (like those in the Ti/Al/Ni/Au metallization) have not been generated. This has refuted the hypothesis of the balling-up of the molten Al–Ni alloy on the surface of the Ti/Al/Ni metallization. To reduce the amount of an Au–Al liquid phase formed during the annealing, which is the reason that renders the Ti/Al/Ni/Au metallization surface rough, the Au layer thickness was reduced to a minimum, at which the contrast of the metallization elements to the semiconductor surface is sufficient for self-aligning during electron-beam lithography. It has been found that the 50-nm-thick Au layer serves a satisfactory contrast. At such a thickness of the Au layer, the metallization surface morphology improved considerably: the roughness decreased from 300 to 80 nm, and the surface become specular.

Annealing of contact system Ti/Al/Ni/Au for the Ohmic contact formation to the AlGaN/GaN was performed. Method for determining the height of potential barrier in nonrectifying contact using voltage-capacitance characteristic was proposed. Temperature dependencies of the contact resistance for annealed Ti/Al/Ni/Au in temperature range 25÷175 °C were obtained. Thermal field emission prevails in rectifying contact, whereas for nonrectifying contact field emission is typical. It is shown that the charge carriers’ concentration increase in four times influences on the transition from thermal field emission to field emission. The change of resistance under field emission agrees with the barrier height change. The resulting contact resistance for Ti/Si(6 nm)/Ti/Al/Ni/Au is equal to 0.2 Ω·mm.

This paper studies the properties of ITO films obtained by electron beam evaporation in a wide range of conditions: oxygen pressure from 5 × 10−4 to 4 × 10−2 Pa and the evaporation rate of 0.075–0.4 nm/s. Evaporation was carried out from granules of 3–6 mm, which consisted of a mixture of stoichiometric indium oxides and tin in the ratio of 9: 1. The deposition rate was maintained constant by a quartz sensor of deposition speed and film thickness. Evaporation was stopped upon reaching a predetermined film thickness of 200 nm. After applying the film, the samples were annealed for 30 s in nitrogen or air at a temperature of 300–700°C. The properties of the obtained films were studied in order to select the optimum deposition conditions and subsequent annealing. The ITO films obtained under optimal conditions were successfully used in structures of LEDs as transparent conductive contacts based on GaN.

This paper is dedicated to the experimental investigation of Ohmic contacts to the n+-doped region of AlGaN/GaN transistor heterostructure based on Ti/Si/Ti/Al/Ni/Au metallization. Effect of annealing temperature on the specific resistance of Ohmic contact was studied. Ohmic contact with the resistance of 3.4·10-6 Ω·cm2 was formed by optimization of the annealing temperature and introduction of the additional doping silicon layer.

In this article, we have studied the influence of Si3N4 and SiO2 thin film gate dielectrics on the current-voltage characteristics of the graphene-based transistor. The test structure of graphene transistor was fabricated with the top and back gate. Graphene has been produced by chemical vapor deposition, and then transferred to the silicon dioxide on a silicon wafer. The channel of the transistor has been formed by etching in oxygen plasma through a photolithographic mask. Metals electrodes of the drain, source, and gate were deposited by resistive evaporation in a vacuum. It was used titanium / aluminum with a thickness of 50/200 nm. In the case of the back gate, silicon dioxide was used, obtained by thermal oxidation of the silicon substrate. For top gate was used silicon nitride deposited by plasma chemical deposition. It was demonstrated that field effect is more pronounced for the case of SiO2 back gate compare to the Si3N4 top gate. For the SiO2 back gate we have observed that the source- drain current decreases, from 2 mA to 3 mA, with increasing the gate voltage, from 0 to 40 V, at constant source-drain voltage, 2 V. In case of Si3N4 top gate the modulation of source-drain current was not significant for the comparable electric field strength. Based on the value of gate voltage for current minima in transfer function the poor quality of Si3N4 –graphene interface is concluded.

The excitation and emission spectra of red photoluminescence of Si wire nanostructures were studied in dependence on surface morphology and influence of magnetic field. The magnetic field of 0.5 T reduced the emission intensity by 10% at all emission spectral range. Comparison of the two photoluminescence models – the quantum confinement and the hot carrier ballistic ones – favours the second model based on the assumption of the excitation of interface oxide defect related luminescence by hot quazi-ballistic carriers created by illumination. The effective mobility of hot electrons is estimated as 6000 cm2/Vs, which greatly exceeds normal electron mobility (1900 cm2/Vs) in Si and thus confirms the presence of hot carrier ballistic motion. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Two nanostructured Sol-Gel composite materials for application in solar cells engineering were created and studied: the TiO 2 /SiO 2 films for antireflecting coatings of cells, and PMMA/SiO 2 insulating layers on metal substrate for efficient heat extraction from a cell. Structural and optical investigation of the first composite proved that its parameters are adequate to serve the purpose; when doped with the dye absorbing UV light and emitting in the visible, it could also increase quantum yield of a cell. The second composite is designed for use in a hybrid PV/Thermal system, where it could optimize the heat exchange between a cell and solar plane collector, which also leads to an increase of efficiency of the system.

The hybrid PV–thermal system was studied, with the photovoltaic panel (PVP) area much smaller than that of the solar collector. Performance of the different panels in the system was investigated, in particular, those made of crystalline (c-) Si, α-Si and CuInSe2 as well as different materials and constructions for the thermal contact between the panel and the collector. Our conclusion is that the PVP for application in a hybrid system needs a special design providing efficient heat extraction from it. PVP was designed and made. Its study has shown that this design provides the high electrical and thermal efficiency of the hybrid system.

This article is devoted to the experimental study of the ohmic contacts based on Ti/Al/Ni/Au metallization to the n+-doped region of the AlGaN / GaN heterostructure. Formed phases are studied at different temperatures. Based on the thermodynamic analysis of possible intermetallic reactions in the contact region, the optimum temperature range was found for the formation of ohmic contacts with a low contact resistance. The optimality of the modeled range is experimentally confirmed.

This paper is dedicated to the experimental investigation of Ohmic contacts to the n+-doped region of AlGaN/GaN transistor heterostructure based on Ti/Si/Ti/Al/Ni/Au metallization. Effect of annealing temperature on the specific resistance of Ohmic contact was studied. Ohmic contact with the resistance of 3.410-6 Ωcm2 was formed by optimization of the annealing temperature and introduction of the additional doping silicon layer.

The kinetics of the amorphous-to-crystalline (fcc) phase transition under isothermal treatments has been investigated in alloys with the composition close to Ge22Sb22Te56, which is the most frequently used for the erasable optical memory devices. For monitoring the transformation, electrical, ellipsometric, optical transmission and electron microscopy measurements were employed. A procedure to determine the transformed volume fraction based on the electrical conductivity data is proposed. It is shown that the widely accepted assumption about the linear dependence between the conductivity variation and the transformed volume fraction is not correct. The use of this assumption could give an error in the determination of the crystalline volume fraction of up to one order of magnitude. The amorphous-to-crystalline transformation kinetics observed agrees with the Johnson–Mehl–Avrami formalism. The transformation exhibits two distinct stages that are attributed to the surface and bulk nucleation, and gives an a...

In this article we have studied the current-voltage characteristics of the graphene- based transistor. The test structure of graphene transistor was fabricated with the back gate. Graphene has been produced by chemical vapor deposition, and then transferred to the silicon dioxide on a silicon wafer. The channel of the transistor has been formed by etching in oxygen plasma through a photolithographic mask. Metals electrodes of the drain, source and gate were deposited by resistive evaporation in a vacuum. It was used titanium / gold with a thickness of 20/200 nm. In the case of the back gate, silicon dioxide was used, obtained by thermal oxidation of the silicon substrate. The field effect was demonstrated. With IV curves graphene parameters were defined.

Synthetic boron-doped p-type single crystals of diamond possess a low-resistance surface layer. The photoconductivity of the bulk high-ohmic region exponentially increases with the increase of temperature. The activation energy of this dependence is 0.4 eV at low electric field and 0.3 eV at high field. The change of activation energy is explained on the basis of the hydrogen-like model of the boron acceptor center. In high electric field the electric current instability is observed connected with the deep levels recharging and thermal breakdown phenomena.

The SiO 2 glasses obtained by the sol-gel process, doped with Fe or Cu and annealed either at oxidizing or at reducing (CO - CO 2 ) atmosphere, exhibit deep coloring caused by the absorption and scattering bands in the visible spectral region followed by a considerable change of the shape of the infra-red absorption bands in the region 1000 - 1250 cm -1 corresponding to the optical phonon's excitation. An analysis is made of the spectra obtained by the optical and photoacoustic as well as by the Raman techniques; results are compared with the theory taking into account the light absorption and scattering for the visible region and the influence of the phonons' scattering on the shape of the corresponding absorption bands for the infra- red region. We found that the coloration caused by the annealing of the doped glass at 100 degree(s)C is basically due to the individual Cu and Fe ions in interstitial sites. After annealing at 300 degree(s)C and higher temperatures in oxygen atmosphere the doping atoms enter substitutionally for Si; part of them form colloidal particles of the corresponding metal oxide. The latter exhibit both absorption and scattering which determine the glass color. Annealing under reduction conditions leads to the formation of Cu and Cu 2 O particles producing a deeper coloration; interaction of the former particles with carbon (graphite) coating causes a specific changes in the Raman spectra which could be attributed to the SERS - Surface Enhanced Raman Scattering.

A brief review is made of some classic and novel experimental techniques allowing the determination of the main parameters of semiconducting materials with the application of purely optical excitation. Among them some modifications of the photothermoacoustical method (in particular, with the pulse excitation), plasma reflection, sample scanning with the intense light beam.