Papers by Keyword: Barrier Height

Abstract: Modeling of Pd/ZnO Schottky diode has been performed together with a set of simulations to investigate its behavior in current-voltage characteristics. The diode was first fabricated and then the simulations were performed to match the IV curves to investigate the possible defects and their states in the bandgap. The doping concentration measured by capacitance-voltage is 3.4 x 1017 cm-3. The Schottky diode is simulated at room temperature and the effective barrier height is determined from current voltage characteristics both by measurements and simulations and it was found to be 0.68eV. The ideality factor obtained from simulated results is 1.06-2.04 which indicates that the transport mechanism is thermionic. It was found that the recombination current in the depletion region is responsible for deviation of experimental values from the ideal thermionic model deployed by the simulator.

Abstract: The behavior of 200nm Cr Schottky contacts on n-type 4H-SiC has been investigated with photoelectron spectroscopy (XPS) and standard (I-V and C-V) electrical measurements at different measurement temperatures. A barrier height close to 1.2 eV was calculated from XPS data under no-current and no-bias conditions on ultra-thin Cr films grown in-situ under UHV conditions. The I-V measurements on as-deposited contacts resulted in a barrier height of 1.06 eV while a value of 1.2 eV has been extracted from the C-V measurements.

Abstract: We present the variation of trap assisted conduction current through a dielectric stack comprising TiO2 and SiO2 on SiC as a function of both temperature and hydrogen gas concentration. We show that the current can be modeled by the use of a single barrier height across the temperature range of interest (>300oC ambient). Upon exposure to hydrogen gas, this barrier height is reduced from 0.405 to 0.325eV, whilst the density of traps in the bulk of the TiO2 remains unaffected. We conclude that the formation of a charge dipole layer under the palladium contact is responsible for this change in barrier height, as has been observed in Schottky diode sensor structures. Further, sensing the gas concentration by monitoring of the trap assisted conduction current appears not to be influenced by the existence of interfacial traps, offering the chance to fabricate low drift sensors for deployment in extreme environments.

Abstract: MTJs of structure Si/SiO2/Ta/Ru/IrMn/CoFe/Ru/CoFe/Al-O/CoFe/NiFe/Ru with different surface roughness of bottom electrode were prepared by sputtering, and it was investigated that the dependence of TMR ratio and resistance-area product (RA) on plasma oxidation time, thickness and surface roughness of tunnel barrier, and the tunneling characteristics of junction devices through I-V curves. To get resistance of below RA 10 kΩμm2, oxidation time of 10 s for 8 Å thick Al layer was required. In this case, thickness of Al2O3 barrier layer was 12.5 ~ 14 Å. For the 13 Å thick Al2O3 tunnel barrier, TMR ratio of optimized MTJ with uniform tunnel barrier was about 45% at bias voltage of 100 mV. Also the barrier height and the barrier width fitted to Simmon's relation were 12.3 Å and 3.07 eV, respectively, and these values agreed with that of MTJ within error range. The I-V curve and TMR ratio versus bias voltage curve of MTJ with rough tunnel barrier were linear and asymmetric, respectively, but in case of MTJ with uniform tunnel barrier, these curves were non-linear and symmetric, respectively. It was confirmed that the smooth surface of bottom electrode was a basic requirement for MTJ.

Abstract: Low-temperature post-oxidation annealing (POA) process of high-reliability thermal oxides grown on 4H-SiC using new apparatus that generates atomic hydrogen radicals by high-temperature catalyzer has been investigated. Atomic hydrogen radicals were generated by thermal decomposition of H2 gas at the catalyzer surface heated at high temperature of 1800°C, and then exposed to the sample at 500°C in reactor pressure of 20 Pa. The mode and maximum values of field-to-breakdown are 11.0 and 11.2 MV/cm, respectively, for the atomic hydrogen radical exposed sample. In addition, the charge-to-breakdown at 63% cumulative failure of the thermal oxides for atomic hydrogen radical exposed sample was 0.51 C/cm2, which was higher than that annealed at 800°C in hydrogen atmosphere (0.39 C/cm2). Consequently, the atomic hydrogen radical exposure at 500°C has remarkably improved the reliability of thermal oxides on 4H-SiC wafer, and is the same effect with high-temperature hydrogen POA at 800°C.

Abstract: Recently Ni/SiC contacts have been studied in order to achieve very low contact resistivity (rc) values on n-type SiC. In this work contact resistivity values of Ni-silicide contacts to n-type ion implanted 6H-SiC are analyzed aiming at extracting the Schottky Barrier Height (SBH). The n-type ion implanted 6H-SiC specimens were annealed at 1300, 1500, 1650°C for 20 min in a high purity Ar ambient. The rc values have been extracted from Transmission Line Method (TLM) measurements in the range of temperatures 25-290°C. The rc values are in the range 1-5×10-5 Wcm2 depending on the annealing temperature. The SBH fBn has been extracted by exploiting the dependence of the contact resistivity on the temperature. By using the field emission model, the value obtained for fBn on our samples is in the range 1.1-1.3 eV depending on the annealing temperature. The SBH on p-type 6H-SiC has been evaluated on Schottky diodes by means of both IV and C-V measurements. A value of qfBp= (1.75±0.05) eV has been obtained on p-type SiC through the C-V method. The average SBH extracted from I-V data collected at room temperature is (1.19±0.03) eV and this value increases as a function of the temperature until (1.50±0.01) eV at 290°C. Differences between values of SBH extracted from I−V and from C−V measurements are explained in terms of inhomogeneous barrier height