N. S. Boltovets

Mechanism of contact resistance formation in ohmic contacts with high dislocation density

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 determined by electron diffusion. It is shown that current flows through the semiconductor near-surface regions where electrons accumulate. A feature of the mechanism is the realization of ohmic contact irrespective of the relation between the contact and bulk resistances. The theory is proved for contacts formed to III-V semiconductor materials as well as silicon-based materials. A reasonable agreement between theory and experimental results is obtained.

Au-TiBx-n-6H-SiC Schottky barrier diodes: Specific features of charge transport in rectifying and nonrectifying contacts

Mechanism of charge transport in a diode of a silicon carbide’s Schottky barrier formed by a quasi-amorphous interstitial phase TiBx on the surface of n-6H-SiC (0001) single crystals with an uncompensated donor (nitrogen) concentration of ∼1018 cm−3 and dislocation density of ∼(106–108) cm−2 has been studied. It is demonstrated that, at temperatures T ≲ 400 K, the charge transport is governed by the tunneling current along dislocations intersecting the space charge region. At T > 400 K, the mechanism of charge transport changes to a thermionic mechanism with a barrier height of ∼0.64 eV and ideality factor close to 1.3.

Thermal-resistant TiB x -n-GaP Schottky diodes

The effect of rapid thermal annealing on the parameters of TiBx-n-GaP Schottky barriers and interphase interactions at the TiBx-GaP interface are studied. It is shown that the contact TiBx-n-GaP system features an increased thermal stability without varying the electrical parameters of the Schottky barrier at temperatures as high as 600°C.

Features of temperature dependence of contact resistivity in ohmic contacts on lapped n-Si

The temperature dependence of contact resistivity ρc 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 ρc(T) curve in the low temperature range, an increasing part is registered with increasing temperature T. It is demonstrated that the formation of contact to a lapped Si wafer results in the generation of high dislocation density in the near-surface region of the semiconductor and also in ohmic contact behavior. In this case, current flows through the metal shunts associated with dislocations. The theory developed is in good agreement with experimental results.

Thermal stability of multilayer contacts on gallium nitride

The results of investigation of a new system of metallization for nonrectifying contacts on n-GaN are presented. The new contact metallization system involves the following sequence of layers: Au(200 nm)-Ti(TiBx)(100 nm)-Al(20 nm)-Ti(50 nm), where the TiBx layer plays the role of a diffusion barrier. The contacts with the TiBx layer retain their layer structure and electrical characteristics upon annealing up to 700°C, whereas the usual Au-Ti-Al-Ti structure exhibits degradation upon rapid thermal annealing at T = 700°C. Further increase in the annealing temperature to 900°C leads to smearing of the layer structure of the Au-TiBx-Al-Ti-GaN contact. Physical factors responsible for the change in the parameters of such contact systems are considered.

Heat-Resistant Barrier Contacts Made on the Basis of TiBx and ZrBx to SiC and GaN

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 °С (1000 °С) for contacts to GaN (SiC 6H). It is shown that the layered structure of metallization and electrophysical properties of Schottky barriers (SBs) remain stable after RTA, thus indicating their heat resistance. The ideality factor n of the I-V characteristic of SBDs after RTA was 1.2, while the SB height φВ was ~0.9 eV (~0.8 eV) for the gallium nitride (silicon carbide) barrier structures.

New technological possibilities for formation of GaAs and InP epitaxial layers for Gunn diodes

We consider a novel technological approach to formation of structurally-perfect indium-phosphide and gallium-arsenide epitaxial n-layers grown on specially prepared porous n+-InP and n+-GaAs substrates. The structural properties of epitaxial layers and output parameters of the Gunn diodes made on their basis were studied. The InP and GaAs epitaxial layers were grown in the same conditions on the standard substrates. The advantages of the epitaxial layers grown on porous substrates and Gunn diodes made on their basis are demonstrated

Heat- and radiation-resistant contacts to SiC made on the basis of quasi-amorphous ZrB2 films

The radiation and thermal stability of the Schottky-barrier structures deposited by the magnetron sputtering of zirconium diboride onto the (0001) face of the Lely-grown n-6H(15R)SiC single crystals with the uncompensated-donor concentration of ∼1018 cm−3 was investigated by the methods of the I–V and C–V characteristics combined with the layer-by-layer Auger analysis. It is shown that the use of quasi-amorphous ZrB2 films when manufacturing contacts on n-6H(15R)SiC leads to no changes in the Schottky-barrier characteristics during rapid thermal annealing to 800°C in the range of 60Co γ-ray irradiation doses of 103–107 Gy.

Properties of GaN(SiC)-(Ti, Zr)B x Contacts Subjected to Rapid Thermal Annealing

The effect of rapid thermal annealing on the structural and physical properties of Au-(Ti, Zr)Bx-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 temperatures as high as 900 and 1000°C, respectively. The stability of interphase boundaries is confirmed by almost constant physical properties of contacts before and after the rapid thermal treatments. The Schottky-barrier height φb amounts to 0.89–0.9 eV for the contacts with GaN and 0.79–0.83 eV for SiC; the ideality factor n of the I–V characteristic amounts to n = 1.2 for the Au-TiBx(ZrBx)-n-GaN(SiC) contacts and n ≈ 1.12 for the Au-ZrBx-n-n+-4HSiC contacts. The structural investigations indicate that there are glass-forming boron and metal oxides at an interphase boundary, which form a thin amorphous vitreous layer resistant against rapid thermal annealing and represent the diffusion barrier for the interphase transport.

Interphase interactions and the mechanism of current flow in Au-TiBx-AuGe-n-GaP ohmic contacts

Au-TiBx-AuGe-n-GaP ohmic contacts have been investigated before and after rapid thermal annealing at T = 723, 773, and 873 K for 60 s in a hydrogen atmosphere. It is shown that the contact resistivity decreases with an increase in temperature in the range 77–232 K due to the thermionic nature of current flow in inhomogeneous ohmic contacts, while in the range 232–386 K the contact resistivity increases, which can be related to the conduction through metal shunts.