Rajendra Solanki

Directed growth of nickel silicide nanowires

Deposition of nickel silicide nanowires has been achieved in the temperature range of 320 to 420 °C by decomposition of silane on nickel surfaces. The substrates consisted of Ni foils and thin Ni films (∼10–100 nm) evaporated on 1-μm-thick layers of SiO2 predeposited on Si wafers. Nanowire growth between two metal pads was achieved with aid of an electric field. It was found that thinner diameter nanowires were produced at low temperatures and that the density of the nanowires was dependent on the reactor pressure. The current–voltage relationship of these nanowires has also been examined.

Electron spin resonance study of interface defects in atomic layer deposited hafnium oxide on Si

We report electron spin resonance (ESR) observation of interface defects at the HfO2/(111)Si boundary for HfO2 films deposited via atomic layer chemical vapor deposition using Hf(NO3)4 as a precursor. We observe several signals, dominated by one due to a silicon dangling bond at the Si/dielectric interface. This center is somewhat similar to, but not identical to, Si/SiO2 interface silicon dangling bonds. Comparison between ESR and capacitance versus voltage measurements suggests that these dangling bond centers play an important role in HfO2/Si interface traps.

Electrical properties of HfO2 deposited via atomic layer deposition using Hf(NO3)4 and H2O

We report on the electrical properties of HfO2 deposited via atomic layer deposition using Hf(NO3)4 precursor for metal/oxide/semiconductor gate dielectric applications. Thin films, with less than 1% variation in accumulation capacitance over a 150 mm wafer, have been deposited directly on hydrogen-terminated Si wafers. The effective dielectric constant of thin (<10 nm) films was in the range of κeff=10–12, the breakdown voltage was about 6–9 MV/cm, and the leakage current was between 3–6 orders of magnitude lower than that of SiO2. The relative benefit of lower leakage current of HfO2 over SiO2 decreased with decreasing effective thickness. Electron trapping was observed under constant voltage stressing.

Violet light emitting SrS/SrCl:Eu thin‐film electroluminescent devices

Emission of bright (over 9 cd/m2) violet light centered at 404 nm has been achieved from SrS:Eu thin‐film electroluminescent (EL) devices. The brightness has remained stable after several hours of operation. The source of this light is believed to be the 5d–4f transition of Eu2+ in the SrCl2 host, which is formed near the ZnS/SrS interfaces within the sandwich structure of the EL devices. Similar device structures were also utilized to produce ultraviolet EL emission at 367 nm from SrCl2:Ce3+ layers. These devices were grown via atomic layer epitaxy.

Atomic layer epitaxy of ZnS:Tb thin film electroluminescent devices

Fabrication of green light emitting ZnS:Tb thin film electroluminescent devices using atomic layer epitaxy is described. In this investigation, particular emphasis is placed on the effect of Tb doping profiles and concentrations on the emission characteristics. It is shown that rapid thermal anneal of these devices has a significant effect on their emission lifetimes.

Atomic Layer Chemical Vapor Deposition of Hafnium Oxide Using Anhydrous Hafnium Nitrate Precursor

HfO 2 films have been deposited using anhydrous hafnium nitrate (Hf(NO 3 ) 4 ) as a precursor for atomic layer chemical vapor deposition (ALCVD). These films have been characterized using x-ray diffraction, x-ray reflectivity, atomic force microscopy, current vs. voltage, and capacitance vs. voltage measurements. An advantage of this precursor is that it produces smooth and uniform initiation of film deposition on H-terminated silicon surfaces. As deposited films remained amorphous at temperatures below ∼700°C. The effective dielectric constant of the film (neglecting quantum effects) for films less than ∼15 nm thick, was in the range of k film ∼ 10-11, while the HfO 2 layer value was estimated to be kHfO 2 ∼ 12-14. The lower than expected dielectric constant of the film stack is due in part to the presence of an interfacial layer such as HfSiO x . Excess oxygen may play a role in the lower than expected dielectric constant of the HfO 2 layer. Breakdown of HfO 2 films occurred at ∼5-7 MV/cm. Leakage current was lower than that of SiO 2 films of comparable equivalent thickness.

Characteristics of excimer-laser-annealed polysilicon films for application in polysilicon thin film transistor devices

In this work we have investigated the crystallization of PECVD as-deposited amorphous silicon films by excimer laser anneal. A lambda-physik XeCl excimer laser was used to produce thin polysilicon films under a variety of operating conditions. The effect of process parameters, such as laser energy density, substrate temperature and annealing ambient was investigated with respect to the grain size and surface roughness of the crystallized films. It was found that annealing in rough vacuum, at a substrate temperature of 450 degrees C and with an energy density of 270mJ/cm2 resulted in films with an average grain size of 0.5micrometers and surface roughness of 6nm. It was shown that by introducing a two-step anneal, the distribution of the grain size could be improved with a small compromise in the average grain size. The annealing ambient was shown to significantly affect the surface roughness of the films, with O2-rich environments generally promoting the development of roughness. Incorporation of a barrier layer under the annealed film was shown to increase the grain size and, tat the same time, improve the resistance of the substrate to laser-induced roughening.

Simulation of transient temperature profiles during ELA and relation to process parameters

We have developed excimer-laser-annealing modeling capability by broadening the computational ability of a standard finite-element based computational-fluid-dynamics software package to adopt to the specific demands of very rapid heating of thin a-Si films. This was achieved by the incorporation of a subroutine employing a phase function and a set of rules for determining latent heat absorption or release. Wit this enhancement the model was able to correctly calculate the degree of superheating/undercooling in the film and track the melt-solid interface velocity. The model also provided reasonable estimates of the expected poly-Si lateral growth length as a function of the laser irradiation scenario. The model in its current form is a useful tool for first order calculations and for supporting relevant experimental studies.

Modeling laser beam spatial separation effects for projection laser crystallization

A model for projection laser crystallization of thin silicon films has been developed. The model is capable of simulating stochastic nucleation and grain growth to predict the extent of lateral growth (LG) in the film and the details of the final microstructure. This model was used to simulate irradiation schemes involving multiple pulses, designed to increase the lateral growth length (LGL) in the irradiated domain. For an irradiation scheme involving two pulses, with an adjustable time delay, our simulation predicted a maximum increase in LGL of about 50% (from 2μm to 3μm) with a maximum film temperature of ~2700 K. For a three-pulse irradiation scheme (without time delay) a 50% increase in LGL was also predicted, but with a maximum film temperature of ~2200 K. These simulations show the efficacy and the relative merit of each of the examined schemes, as well as, their associated process window.