Volodymyr Sheremet

• PhD
• Postdoctoral Researcher at Virginia Commonwealth University

A field-effect photodetector structure composed of an Al 2 O 3 -encapsulated bilayer graphene conductive channel attached to an Al 2 O 3 dielectric layer deposited on a HgCdTe absorbing layer on CdTe/Si <211> was studied. Ti/Au ohmic contacts to the graphene layer were used as drain and source electrodes and back-gate voltage was applied to the Si...

Halide perovskite lasers based on CsPbBr3 micro‐ and nanoscale crystals have demonstrated fascinating performance owing to their low‐threshold lasing at room temperature and cost‐effective fabrication. However, chemically synthesized thin films of CsPbBr3 usually have rough polycrystalline morphology along with a large amount of crystal lattice def...

In this work, the effect of introducing a photonic crystal network of silicon nitride (SiN) micro-domes on the backside of silver coated gallium nitride (GaN) based light emitting diodes (LEDs) was studied. First, sapphire side of the top emitting LEDs, which is the bottom surface of the LEDs, is coated with silver (Ag). Light emitted towards the s...

The temperature dependences of the specific contact resistance of silicon roc with a doping step are measured experimentally and described theoretically. The measurements are performed in the temperature range from 4.2 to 380 K. It is established that the contacts of the studied Au–Ti–Pd–n+–n-Si structures are ohmic. It is shown that minimal roc is...

We investigate the effect of InGaN stress compensation layer on the properties of light emitting diodes based on InGaN/GaN multiple quantum well structures with step-graded electron injectors. Insertion of an InGaN stress compensation layer between n-GaN and the step graded electron injector provides, among others, strain reduction in the MQW regio...

Enhancement of InGaN/GaN based light emitting diode performance with step graded electron injectors through a two-step passivation is reported. Perimeter passivation of LED dies with SiO2 immediately following ICP mesa etch in addition to conventional Si3N4 dielectric surface passivation leads to decrease in the reverse bias leakage current by a fa...

The effect of a transparent ITO current spreading layer on electrical and light output properties of blue InGaN/GaN light emitting diodes (LEDs) is discussed. When finite conductivity of ITO is taken into account, unlike in previous models, the topology of LED die and contacts are shown to significantly affect current spreading and light output cha...

Resistivity ρc of InP- and GaAs-based ohmic contacts has been measured in a temperature range of 4.2–300 K. Both temperature dependences are nonmonotonic and exhibit minima at T = 50 K for InP and T = 150 K for GaAs. The nonmonotonic ρc(T) curves for GaAs contacts have been observed for the first time. The obtained experimental temperature dependen...

The temperature dependences of the contact resistivity (ρc) of ohmic contacts based on the Au–Ti–Pd–InN system are measured at an InN doping level of 2 × 1018 cm–3 in the temperature range of 4.2–300 K. At temperatures T > 150 K, linearly increasing dependences ρc(T) are obtained. The dependences are explained within the mechanism of thermionic cur...

In this paper, we have considered the four-contact method for measurements of the specific contact resistivity of the ohmic contacts (ρ c). The presented method for measuring ρ c has been compared with several other methods. Limits of applying this method have been shown.

The temperature dependence of the contact resistivity ρc (T) of Au-Ti-Al-Ti-n +-GaN ohmic contacts is studied experimentally and substantiated theoretically in the temperature range T = 4.2–300 K. It is shown that the saturation portion of ρc (T) is observed in the low-temperature measurement region (4.2–50 K). As the temperature increases, ρc decr...

It is experimentally found that an ohmic contact based on Au-Pt-Ti-Pd-n +-Si metallization is formed due to nanoscale metal shunts containing Si, Au, and Pt in the region of the interface with n +-Si, which appears during heat treatment at T = 450°C for 10 min in a vacuum chamber with a residual pressure of 10−6 Torr. The high density of shunts adj...

Contact resistivity rc of InP and GaAs based ohmic contacts was measured in the 4.2/300 K temperature range. Nonmonotonic dependences rc(T), with a minimum at temperature 50 K (150 K) for InP (GaAs) based contacts were obtained. The results can be explained within the framework of the mechanism of current flow through metal shunts (associated with...

We present the results of structural and morphological investigations of interactions between phases in the layers of Au-Pd-Ti-Pd-n+-GaN contact metallization that appear at rapid thermal annealing (RTA). It is shown that formation of ohmic contact occurs in the course of RTA at Т= 900C due to formation of titanium nitride. We studied experimental...

The paper considers ohmic contacts of Au-TiBx -Al-Ti-n-GaN, Au-Pd-Ti-Pd-n-AlN and Au-Pd-Ti-n-C to the promising for use in microelectronics wide-gap semiconductors. Ohmic contact formation takes place after sequential layering of metal with further fast thermal processing, which leads to solid-phase reactions between the semiconductor and metal. It...

The temperature dependences of the contact resistance ρc (T) of ohmic Pd-Ti-Pd-Au contacts to n-GaN and n-AlN wide-gap semiconductors with a high dislocation density are studied. The dependences ρc (T) for both contacts contain portions of exponential decrease ρc (T) and very weak dependence ρc (T) at higher temperatures. Furthermore, a plateau por...

The temperature dependence of contact resistivity ρ с of Ti-Al-TiB2-Au ohmic contacts to n-GaN and effect of microwave treatment on ρ с are investigated. The obtained dependences are described using a model of current flow via metal shunts associated with dislocations, the current being limited by diffusion supply of electrons. It is shown that...

Anomalous temperature dependences of the specific contact resistance ρc (T) of Pd2Si–Ti–Au ohmic contacts to lapped n�Si with dopant concentrations of 5 ×1016, 3 ×1017, and 8 ×1017cm–3 have been obtained. The anomalous dependences of ρc (T) have been accounted for underthe assumption that the current flows along nano-dimensional metallic shunts, wh...

We studied Au-Pd-Ti-Pd ohmic contacts made by thermal evaporation of metals in vacuum onto n-GaN (n-AlN) with high dislocation density heated to a temperature of 350 °�. Temperature dependence of ohmic contacts resistivity may be described by the mechanism of current flow through the metal shunts associated with dislocations, with allowance made fo...

We studied Au-Pd-Ti-Pd ohmic contacts made by thermal evaporation of metals in vacuum onto n -GaN (n -AlN) with high dislocation density heated to a temperature of 350 °C. Temperature dependence of ohmic contacts resistivity may be described by the mechanism of current flow through the metal shunts associated with dislocations, with allowance made...

We present experimental results concerning a high density of structural defects (in particular, dislocations) in the near-contact region of heavily doped n-silicon. They appear in the course of firing Au Pd Ti Pd –Si -n ohmic contact at 450 С for 10 min in a vacuum of ~10 Pa-4. These defects lead to appearance of metal shunts that determine the cur...

We studied, both theoretically and experimentally, temperature dependences of contact resistivity, ρc(T), of ohmic contacts to n+-GaN. The ρc(T) curves have saturation portion at low temperatures (4.2-50 K) and exponential portion as temperature grows up to 300 K. For comparison we also give the reference data on ρc(T) for ohmic contacts to n+-GaAs...

We studied ohmic contacts Au-Pd-Ti-Pd-n-AlN and Au-TiB2-Al-Ti-n-GaN with contact resistivity $rho$с = 0.18 Ohm*cm^2 and 1.6*10^-4Ohm*cm^2, respectively, and the effect of microwave treatment on their electrophysical properties. After microwave treatment for time t up to 1000 s, the contact resistivity dropped by 16% (60%) in the contact to AlN (GaN...

We studied temperature dependences of resistivity, , of Pd-Ti-Pd-Au ohmic contacts to wide-gap semiconductors n-GaN and n-AlN with high dislocation density. Both curves have portions of exponential decrease, as well as those with very slight dependence at higher temperatures. Besides, the Au-Pd-Ti-Pd-n-GaN contacts have a portion of flattening out...

The temperature dependence of contact resistivity qc in lapped silicon specimens with donor concentrations of 5*1016, 3*1017, and 8*1017 cm-3 was studied experimentally. We found that, after decreasing part of the qc(T) curve in the low temperature range, an increasing part is registered with increasing temperature T. It is demonstrated that the fo...

A new mechanism of contact resistance formation in ohmic contacts with high dislocation density is proposed. Its specific feature is the appearance of a characteristic region where the contact resistance increases with temperature. According to the mechanism revealed, the current flowing through the metal shunts associated with dislocations is dete...

Temperature dependences of the contact resistivity ρc of Au-TiBx -Ge-Au-n-n +-n ++(GaAs)-InP ohmic contacts before and after short-term (10 s) microwave treatment have been studied both experimentally and theoretically. It is shown that ρc can decrease after microwave treatment in the entire temperature range of ρc measurements (100–400 K). Good ag...

Based on a theoretical analysis of the temperature dependence of the contact resistance R c for an Au-Ti-Pd2Si-n +-Si ohmic contact, a current-transfer mechanism explaining the experimentally observed increase in R c in the temperature range 100–380 K is proposed. It is shown that microwave treatment of such contacts results in a decrease in the sp...

A new mechanism describing the rise in the contact resistance ρc of ohmic contacts to n-n +-n ++-GaAs(GaP, GaN, InP) structures with increasing measurement temperature T, experimentally observed in the temperature range 100–400 K, is suggested on the basis of a theoretical analysis of the temperature dependence of ρc . Good agreement between the ex...

We studied temperature dependences of resistivity ρc(T) of Pd-Ti-Pd-Au ohmic contacts to wide-gap semiconductors n-GaN and n-AlN with high dislocation density. The obtained dependences cannot be explained by the existing mechanisms of current flow. We propose possible mechanisms explaining the experimental ρc(T) curves for ohmic contacts to n-GaN a...

Some aspects of measuring the thermal resistance to a constant heat flow at a p-n junction–package region in IMPATT and light-emitting diodes are considered. We propose a method of studying the thermal resistance of high-power light-emitting diodes. This method makes it possible to increase accuracy of measuring the thermal resistance by determinin...

We investigated temperature dependence of contact resistance of an Au-Ti-Pd2Si ohmic contact to heavily doped n+-Si. The contact resistance increases with temperature owing to conduction through the metal shunts. In this case, the limiting process is diffusion input of electrons to the metal shunts. The proposed mechanism of contact resistance form...

Based on a theoretical analysis of temperature dependence of contact resistance RC for Au-Ti-Pd2Si-n+-Si oh-mic contact, a current flow mechanism is proposed that explains the experimentally observed RC growth with temperature in the 100-380 K temperature range. It is shown that microwave treatment of such contacts leads to reduction of RC values s...

We propose multilayer ohmic contacts to n-and p-GaN layers, with titanium boride as diffusion barrier. It is shown that the optimal method of contact resistivity measurement is the transmission line method (TLM) with circular contact geometry. The Ti−Al−TiB x −Au contact metallization to n-GaN retains its layer structure after thermal annealing at...

The radiation resistance of Au–Pd–Ti–Pd–n++InP ohmic contacts and Au–TiBx–n-n+-n++InP barrier contacts—both initial and subjected to a rapid thermal annealing and irradiated with 60Co γ-ray photons with doses as high as 10 9 R—has been studied. Before and after external effects, the electrical characteristics of the barrier and ohmic contacts, dist...

The temperature dependences of the contact resistivity ρ{sub c} of Au-TiBâ Al-Ti-n{sup +}-n-n{sup +}-GaN-AlâOâ ohmic contacts have been studied before and after microwave treatment followed by nine-nonth room-temperature sample storage. The temperature dependences of ρ{sub c} of initial samples were measured twice. The first measurement showed th...

The radiation resistance of Au-Pd-Ti-Pd-n ++-InP ohmic contacts and Au-TiBx-n-n +-n++-InP barrier contacts—both initial and subjected to a rapid thermal annealing and irradiated with 60Co γ-ray photons with doses as high as 109 R—has been studied. Before and after external effects, the electrical characteristics of the barrier and ohmic contacts, d...

The effect of ionizing radiation of 60Co γ-ray photons in the dose range 104–2 × 109 rad on metal-semiconductor Au-ZrBx -AlGaN/GaN and Au-TiBx -Al-Ti-n-GaN contacts and Au-ZrBx -n-GaN Schottky diodes is examined. The contacts with the TiBx and ZrBx diffusion barriers do not degrade under the effect of ionizing radiation if the dose does not exceed...

Modern methods of measuring resistance of ohmic contacts are considered in the review: Cocks-Strack, transmission line, Kelvin, boundary probing. Examples of their application are provided and errors of measuring the contact resistivity are calculated. The most accurate measuring methods are the Kelvin method and the boundary probing method, while...

The effect of rapid thermal annealing on the structural and physical properties of Au-(Ti, Zr)B x-GaN(SiC) contacts and diode structures on their basis is investigated. The X-ray-diffraction investigations and the layer-by-layer Auger analysis showed that the phase composition and structure of the GaN and SiC contacts are retained to the temperatur...

Radiation effects in the Au-Ti-Al-Ti-n-GaN multilayer metallization subjected to irradiation with 60Co γ-ray photons in the dose range 4 × 106−2 × 107 Gy are considered, and the effect of radiation on the initial contact structures and the structures subjected to a rapid thermal annealing (RTA) at high-temperature in the nitrogen atmosphere is stud...

We studied the heat resistance of Au-TiBx (ZrBx) barrier contacts to n-SiC 6H and n-GaN. The Schottky barrier diode (SBD) parameters, the concentration depth profiles for contact structure components and the phase composition of contact metallization were measured both before and after rapid thermal annealing (RTA) at temperatures up to 900 °C (100...

We investigated thermal stability of Au-TiBx (ZrBx) barrier contacts, as well as ohmic contacts with a TiBx diffusion barrier to n-Si (GaAs, InP, GaP, GaN, SiC). The electrophysical measurements of Schottky barrier diodes and ohmic contacts were performed both before and after rapid thermal annealing (RTA) up to 600 °С for the structures on Si, GaA...

We studied the effect of microwave irradiation (frequency of 2.45 GHz, irradiance of ~1.5 W/cm2) for 2-100 s on the characteristics of Au-TiBx-Al-Ti-n-GaN contact structures. A correlation between the contact resistivity changes and wafer curvature was found. This indicates considerable effect of intrinsic stresses on contact resistivity. Relative...

A mechanism of charge transport in Au-TiBx -n-GaN Schottky diodes with a space charge region considerably exceeding the de Broglie wavelength in GaN is studied. Analysis of temperature dependences of current-voltage (I–V) characteristics of forward-biased Schottky barriers showed that, in the temperature range 80–380 K, the charge transport is perf...

We investigated a current flow mechanism in the Au−TiBx−n-GaN−i-Al2O3 Schottky barrier diodes, in which the space-charge region width is much over the de Broglie wavelength in GaN. An analysis of the temperature dependences of the I−V curves of forward-biased Schottky barriers showed that, in the temperature range 80−380K, the current flow occurs a...

High-stable heat-resistant low-resistance contact systems with diffusion barriers involving quasi-amorphous TiB x layers are suggested and studied. We have performed the structural and morphological investigations along with studies of Auger concentration depth profiles in the contacts both before and after rapid thermal annealing. It is found that...

We investigated a current flow mechanism in the Au−TiBx−n-GaN−i-Al2O3 Schottky barrier diodes, in which the space-charge region width is much over the de Broglie wavelength in GaN. An analysis of the temperature dependences of the I−V curves of forward-biased Schottky barriers showed that, in the temperature range 80−380 K, the current flow occurs...