Papers by Keyword: Trapping

Abstract: GaN power HEMTs enable the design of power electronic systems with highest efficiencies and reduced size. Despite strong advancements in device reliability, charge carrier trapping is still an important challenge. The applied methodology allows to characterize defects that cause the dynamic R_DS,on in GaN power devices at product level with flexibility in duty cycle, number of pulses and mission profile. A pronounced trapping is observed for lateral GaN-on-Si HEMTs with Schottky p-GaN gate structure at low drain bias and long off-state pulses (> 100 ms). The effect is investigated by fast determination of the on-state resistance R_DS,on under different trap capturing conditions: a) different drain bias b) off-state time and number of cycles c) variation of temperature. The trapping and detrapping effects are characterized and the activation energy is extracted from time constants. An elevated on-state resistance was present for up to 3 hours. The threshold voltage modification due to high drain bias does explain the significant R_DS,on increase.

Abstract: This work applies combination of Direct Tunneling model and BSIM4 based ITAT model to explain the leakage of electrons from charged nanocrystals to p-type silicon substrate in data retention condition, for an ultra-thin tunnel oxide, low voltage programmable silicon nanocrystal based flash gate stack. Basic expressions of these models are modified to incorporate the nanocrystals related charge leakage in idle mode. The concept is supported by simulating these models and comparing them with the experimental data. Transition of electrons is considered as a result of Direct Tunneling and their trapping de-trapping via water related hydrogen traps. However, it is found that modified ITAT mechanism is the dominant one. Flat-band voltage shift profile fits accurately with the model with an extrapolated 10 years device lifetime without memory closure. 3 nm thick tunnel oxide and 100 nm sized nanocrystal fabrication with Electron Beam Lithography are main features of the devices.

Abstract: The paper presents the results of both ab initio and thermodynamic analysis of vacancy and divacancy formation and hydrogen interaction with them in alpha (bcc) iron. Ab initio calculations were performed by DFT method using LAPW in WIEN2k package. Monovacancy formation energy was found to be 2.15 eV and divacancy binding energy 0.22 ± 0.01 eV. Equlibrium fraction of vacancies bound into divacancies is of the order of 10^–5 even at the highest temperatures close to bcc → fcc transformation point. Hydrogen has a strong interaction with monovacancies (vacancy-hydrogen binding energy decreasing from 0.60 to 0.31 eV for the first–fifth H atom inside a single vacancy) but has only a small effect on divacancy formation energy that is equal to 0.28, 0.19 and 0.17 for the case of joining of VH + V, VH + VH and VH₂ + VH₂, respectively. This means that the presence of hydrogen cannot significantly increase the equilibrium concentration of divacancies.

Abstract: In this paper, the tooth profile of a kind of full conjugate helical gear pump was designed. The tooth profile of each of the gears is composed of three curves which are an addendum arc, an involute and a dedendum curve. The dedendum curve of one gear is the conjugate curve of the addendum arc of the other gear. The addendum arc and the dedendum curve are joined tangentially by an involute. The equations of the curves were deduced by using differential geometry. The ranges of parameters in these equations were also obtained. The meshing characteristics of the gears were analyzed. Two gears transmit continuously with a fixed ratio. Two gears engage each other point by point continuously along the entire profile and formed a continuous space meshing curve. The trapping oil phenomenon could be eliminated and the sealing property could be better than conventional involute gear pumps. The results of calculation and analysis of an application example showed the theoretical analysis and the practicability of the design were valid.

Abstract: Hall measurements on NO annealed 4H-SiC MOS gated Hall bars are reported in the temperature range 77 K- 423 K. The results indicate higher carrier concentration and lower trapping at increased temperatures, with a clear strong inversion regime at all temperatures. In stark contrast to Si, the Hall mobility increases with temperature for 77 K-373K, above which the mobility decreases slightly. The maximum experimental mobility was found to be ~50 cm² V^-1 s^-1 which is only about 10% of the 4H-SiC bulk mobility indicating that while NO annealing drastically improves trapping, it does not improve the mobility significantly. Supporting modeling results strongly suggest the presence of a disordered SiC channel region.

Abstract: Recent investigations on palladium hydride (Pd-H) showed, for the first time, evidence of formation of vacancy-hydrogen (Vac-H) clusters during Severe Plastic Deformation (SPD) effected by High Pressure Torsion (HPT). Vacancy concentrations produced in Pd-H by this method are extraordinarily high. DSC-scans show that the thermal stability range of vacancies is extended by about 150K due to trapping of hydrogen leading to the formation of vacancy-hydrogen clusters. Recent experiments give evidence that the mobility of the H atoms and/or the vacancies is conditional for the formation of Vac-H clusters during HPT. Results furthermore indicate defect stabilization by hydrogen trapping not only for vacancy-type defects but also for dislocations and grain boundaries.

Abstract: A versatile numerical tool for the simulation of electrical properties of a semiconductor such as minority carrier lifetimes and photoconductivity as a function of defect parameters was developed. Unlike the SRH-model this tool enables to simulate e.g. different measurement conditions and even trapping effects. Contrary to the widely used simulation tool PC1D also non-steady state solutions can be obtained. Furthermore the novel contact less method MDP is presented. Using the example of iron determination the new possibilities arising from combining the novel simulation tool and the method MDP are shown. Simulations for different trapping densities and measurement conditions were executed and exemplary measurements of the trap density and the cross-over point of mc-Si wafers were performed. It was found, that the cross-over point and the sensitivity of iron determination at low level injections is effected by trapping and the chosen non- or steady state measurement conditions.

Abstract: Hydrogen permeation and diffusivity in V1−xNbx alloys (x = 0.25, 0.5 and 0.75) were investigated over a temperature range between 573 and 673 K. The alloy sheets surface-coated with Pd (100 nm) by ion-beam sputtering technique were subjected to the hydrogen permeation measurement with hydrogen pressures less than 3000 Pa. It was found that the hydrogen permeation is strongly suppressed especially at low hydrogen pressures; the hydrogen permeation is considered to be controlled by some surface processes. The V0.50Nb0.50 alloy showed the largest permeability 1.4×10−8 mol H2 m−1s−1Pa−1/2 at 673 K which is larger than that for pure Pd. The diffusivity which was determined from the fitting of the permeation curve decreases with the alloy concentration at both the Nb- and V-rich sides and takes a minimum value at x=0.75. The hydrogen potential obtained by a first-principles calculation showed that V atoms act as trapping centers for hydrogen in the Nb matrix and Nb atoms act as anti-trapping centers in the V matrix.

Abstract: The applicability of the Boltzmann-Matano method for evaluation of a diffusion coefficient and its concentration dependency by line profile analysis is tested on three different (model) systems. All systems involve interstitial diffusion. It is shown that the occurrence of trapping corrupts the applicability of the Boltzmann-Matano method.