A. V. Kuchuk

Mechanism of dislocation-governed charge transport in schottky diodes based on gallium nitride

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 performed by tunneling along dislocations intersecting the space charge region. Estimation of dislocation density ρ by the I–V characteristics, in accordance with a model of tunneling along the dislocation line, gives the value ρ ≈ 1.7 × 107 cm−2, which is close in magnitude to the dislocation density measured by X-ray diffractometry.

Effect of p-n junction overheating on degradation of silicon high-power pulsed IMPATT diodes

The thermal limits of the two-drift impact avalanche and transit-time (IMPATT) diode operating in the pulsed mode in the 8-mm wavelength region with a microwave power as high as 30–35 W have been estimated. It is shown that p-n junction overheat at an operating pulse length of 300 ns and a supply current amplitude of 11.3–15 A amounts to 270–430°C relative to an ambient medium. The temperature limit of junction overheating, above which IMPATT diodes rapidly degrade, was determined as 350°C. The presented results of X-ray phase analysis and depth profiles of Au-Pt-Ti-Pd-Si ohmic contact components confirm thermal limits of the IMPATT diode operating in the pulsed mode.

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.

Features of ZnS-powder doping with a Mn impurity during synthesis and subsequent annealing

Luminescence, electron spin resonance, and X-ray diffraction (XRD) methods were used to investigate the features of ZnS-powder doped by Mn impurity during self-propagating high-temperature synthesis and subsequent annealing. The obtained powder consists of ZnS microcrystals with mainly hexagonal phase (80 ± 5)%. It was found, that after synthesis Mn presents not only in the form of non-uniformly distributed microscopic impurities in ZnS, but also in the form of Mn metal nanocrystals. Thermal annealing at 800°C leads to the additional doping of ZnS from metallic Mn, to the redistribution of the embedded Mn in the volume of microcrystals, and to the ZnS oxidation. At the same time, the ratio between the cubic and hexagonal phases does not change. It was shown that annealing causes a decrease in the concentration of the defects responsible for the luminescence-excitation bands, which correspond to transitions from the ground to the excited states of the Mn2+ ion. As a result of annealing, there is also a change in XRD coherent domain size. Simultaneously, the intensity of peaks in the luminescence-excitation spectrum with wavelengths of 375 and 395 nm was changed. The causes of these changes and the nature of the corresponding bands are discussed.

Structural transformations in ZnS:Cu in the course of thermal annealing

The influence of annealing at 800°C on the photoluminescence, electron spin resonance, and X-ray diffraction spectra of powder-like ZnS:Cu, obtained by the self-propagating high-temperature synthesis of a charge, consisting of Zn, S, and CuCl, is studied. It is shown that variation in the material’s heating rate up to the annealing temperature leads to a nonmonotonic variation in the spectral location and full-width at half-maximum of the photoluminescence band in the blue-green spectral region, as well as in the Mn2+ paramagnetic center concentration. It is established that the cubic and hexagonal ZnS phases, as well as the ZnO and CuZn phases, are present in the powder after synthesis. It is shown that annealing of the obtained powder at 800°C leads to three processes: the transformation of the hexagonal ZnS phase into the cubic phase, the oxidation of ZnS and CuZn, and the diffusion of Cu into the bulk of the ZnS microcrystals from the CuZn phase. A model attributing the observed variations in luminescence and electron spin resonance spectra to the diffusion of Cu and Mn impurities into the microcrystal bulk, particularly from the CuZn phase, and to their accumulation at extended defects is suggested.

Evolution of the deformation state and composition as a result of changes in the number of quantum wells in multilayered InGaN/GaN structures

The methods of high-resolution X-ray diffraction have been used to study the multilayered structures in an InxGa1 − xN/GaN system grown by the method of metal-organic chemical-vapor deposition. A correlation between the strain state (relaxation) of the system, the indium content within quantum wells, the ratio of the barrier/well thicknesses, and the number of quantum wells in the active superlattice is established. It is shown that partial relaxation is observed even in a structure with one quantum well. The results we obtained indicate that the relaxation processes are bound to appreciably affect the optical characteristics of devices.

Heat-Resistant Au-TiBx-n-GaN Schottky Diodes

We studied phase composition and parameters of the ohmic Au-TiB x-Al-Ti-n-GaN and barrier Au-TiBx-n-GaN contacts, both before and after rapid thermal annealing (RTA) at T=870degC for 30 s. The phase composition was studied with X-ray diffraction technique, while the parameters of the ohmic contacts were studied for the transmission line method (TLM) structures and those of the barrier contacts were studied by measuring the forward branches of I-V curves with further calculation of the Schottky barrier (SB) height phiB and ideality factor n. It was found that low-resistance (rhocap(1divide3)times10-6 Omegamiddotcm2 ohmic Au-TiBx-Al-Ti-n-GaN contacts can be formed using RTA. It turned out also that, after RTA at T=870degC for 30s, the SB retains its barrier properties practically unchanged, as compared with the initial sample that has not been exposed to RTA