Tetsuroh Minemura

Crystalline Fraction of Microcrystalline Silicon Films Prepared by Plasma-Enhanced Chemical Vapor Deposition Using Pulsed Silane Flow

Microcrystalline silicon (?c-Si) films have been prepared at 200?C by radio-frequency (rf: 13.56 MHz) plasma-enhanced chemical vapor deposition using pulsed silane flow. The crystalline fraction, Xc(Raman), of ?c-Si films approximately 200 nm thick is quantitatively determined by decomposing Raman spectra into three peaks: crystalline, intermediate (small-grain-size-crystalline), and amorphous. The effects of rf power on Xc(Raman) and hydrogen content, CH, have been studied. Xc(Raman) increases with increasing rf power and tends to saturate; the maximum value of Xc(Raman) is 71%. With increasing rf power CH decreases to a minimum value of 4.5% and then increases. Hydrogen introduction into Si films overlapped with hydrogen elimination is responsible for the increase and saturation of Xc(Raman) with rf power.

Structural Change during Annealing of Amorphous Indium-Tin Oxide Films Deposited by Sputtering with H2O Addition

This paper describes the effects of annealing on electric properties and structure of amorphous indium-tin oxide (ITO) films deposited by sputtering at room temperature and with H2O addition. The film resistivity was increased by annealing at 150–200° C; in this temperature range the growth of ITO crystallites dispersed in the amorphous ITO phase was observed. This increased resistivity was found to be due to decreases in both Hall mobility (µ H) and carrier density (n) of the films. Measurements of thermal desorption spectroscopy revealed that two different adsorption states, in terms of H2O molecules which are due to the hydrogen-bonded H2O and OH species, were formed in amorphous ITO films during film deposition and the subsequent annealing process. Factors in the decreases of µ H and n were discussed on the basis of the experimental results obtained.

Effects of Back-Channel Etching on the Performance of a-Si:H Thin-Film Transistors

Thickness of the a-Si:H layer in the back-channel etched thin film transistor (TFT) was successfully reduced to less than 100 nm, with an accompanying increase in the field effect mobility. The thinning was realized by reducing surface defects of the a-Si:H layer generated in the back-channel overetching step. The relationships between the TFT performance and surface defects, analyzed by spectroscopic ellipsometry, were investigated as a function of a-Si:H thickness and back-channel etching depth.

Thermo-photometric study on phase transitions in sputter-deposited Ag-Zn alloy thin films

The behavior and kinetics of transitions between β, ζ and β phases in a sputter-deposited Ag-50 at %Zn alloy thin film were examined by thermo-photometric technique observing the change of reflectivity with temperature and time. Good observation was made easily and determined activation energy for the β→ζ transition was 220.6 kJ/mol. It seems that the ζ phase should nucleate at the grain edge or the grain boundary of the β phase after site saturation under a zero nucleation rate.

In Situ Optical Measurement Using Optical Fibers for a-Si:H Ultra-Thin Films: Theoretical and Numerical Analysis

A new in situ optical characterization technique, consisting of measuring the transmittance of a multimode optical fiber when depositing a hydrogenated amorphous silicon (a-Si:H) thin film on the unclad core, is theoretically and numerically analyzed. Due to a large interferential effect, an apparent increase of the optical gap occurs when decreasing the film thickness below 10 nm. The same effect allows the measurement of the absorption coefficient at a given wavelength in the mid-gap region, lower than 5 cm-1 for 20-nm-thick films. The method is a promising tool to investigate the Density of States (DOS) of a-Si:H ultra-thin films.

Accurate Determination of the Urbach Energy of a-Si:H Thin Films by Correction for the Interference Effect.

The absorptance spectra of a-Si:H films thinner than 0.5 µm are distorted by the presence of only a few interference fringes, which makes the determination of the Urbach energy (UE) difficult. The interference effect is analyzed by computing the absorptance spectrum as a function of the films thickness t. The difference between the UE derived by exponential interpolation and the actual UE reaches a maximum of 17 meV for t ≈220 nm, and it can not be neglected even for films thinner than 100 nm. We measured the photothermal deflection spectroscopy spectra for several film thicknesses and corrected the UE by numerically fitting the spectra.

Order-Disorder Transition in Sputter-Deposited Silver-Zinc Alloy Films

An order-disorder transition between β and β phases was observed to take place reversibly at 510 K in sputter-deposited AgZn alloy films of 30 nm thickness. The β phase was found to exist in the as-deposited alloy film and the transition could be described by the order parameter of Bragg-Williams theory.