六方InN薄膜的载流子输运特性研究

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Temperature effects on optical properties of InN thin films

Transmission measurements have been carried out on InN thin films grown by radio frequency magnetron sputtering on a sapphire (0001) substrate at 10–300 K. With the aid of a novel procedure developed for analyzing the transmission spectra, the effect of temperature on optical properties, such as the absorption coefficient, band-gap, Urbach bandtail characteristics, refractive index and extinction coefficient, of InN thin films has been determined. The wavelength and temperature dependence of the absorption coefficient in both the Urbach and intrinsic absorption regions has been described by a series of empirical formulae. The temperature dependence of the refractive index dispersion below the band-gap is also found to follow a Sellmeier equation. These formulae are very useful for the characterization and device design of InN films. The free-electron concentration in the InN thin film determined here is also found to be in good agreement with that obtained from infrared reflection measurements. PACS 78.66.Fd; 78.40.Fy; 78.20.Bh; 78.20.Ci     

Direct current magnetron sputtering deposition of InN thin films

In this paper, InN thin films were deposited on Si (1 0 0) and K9 glass by reactive direct current magnetron sputtering. The target was In metal with the purity of 99.999% and the gases were Ar (99.999%) and N₂ (99.999%). The properties of InN thin films were studied. Scanning electron microscopy (SEM) shows that the film surface is very rough and energy dispersive X-ray spectroscopy (EDX) shows that the film contains In, N and very little O. X-ray diffraction (XRD) and Raman scattering reveal that the film mainly contains hexagonal InN. The four-probe measurement shows that InN film is conductive. The transmission measurement demonstrates that the transmission of InN deposited on K9 glass is as low as 0.5% from 400 nm to 800 nm.     

Growth of InN thin films on ZnO substrate by plasma-assisted molecular beam epitaxy

We have studied the microstructure property of InN epitaxial films grown on ZnO substrate by plasma-assisted molecular beam epitaxy. We found that the In₂O₃ compound was produced on ZnO substrate and many pits were formed on the InN films when InN was directly grown on ZnO substrate with the N/In flux ratio less than 40. We demonstrated that the quality of InN film was significantly improved when the In₂O₃ layer was used as a buffer to prevent the reaction between In and the ZnO substrate.     

Resonant infrared pulsed laser deposition of thin biodegradable polymer films

Thin films of the biodegradable polymer poly(DL-lactide-co-glycolide) (PLGA) were deposited using resonant infrared pulsed laser deposition (RIR-PLD). The output of a free-electron laser was focused onto a solid target of the polymer, and the films were deposited using 2.90 (resonant with O-H stretch) and 3.40 (C-H) μm light at macropulse fluences of 7.8 and 6.7 J/cm², respectively. Under these conditions, a 0.5-μm thick film can be grown in less than 5 min. Film structure was determined from infrared absorbance measurements and gel permeation chromatography (GPC). While the infrared absorbance spectrum of the films is nearly identical with that of the native polymer, the average molecular weight of the films is a little less than half that of the starting material. Potential strategies for defeating this mass change are discussed. Received: 22 August 2001 / Accepted: 23 August 2001 / Published online: 17 October 2001     

Nonlinear dynamics in wurtzite InN diodes under terahertz radiation

We carry out a theoretical study of nonlinear dynamics in terahertz-driven n+ nn+ wurtzite InN diodes by using time-dependent drift diffusion equations.A cooperative nonlinear oscillatory mode appears due to the negative differential mobility effect,which is the unique feature of wurtzite InN aroused by its strong nonparabolicity of the Γ 1 valley.The appearance of different nonlinear oscillatory modes,including periodic and chaotic states,is attributed to the competition between the self-sustained oscillation and the external driving oscillation.The transitions between the periodic and chaotic states are carefully investigated using chaos-detecting methods,such as the bifurcation diagram,the Fourier spectrum and the first return map.The resulting bifurcation diagram displays an interesting and complex transition picture with the driving amplitude as the control parameter.     

Nonlinear dynamics in wurtzite InN diodes under terahertz radiation

We carry out a theoretical study of nonlinear dynamics in terahertz-driven n⁺nn⁺ wurtzite InN diodes by using time-dependent drift diffusion equations. A cooperative nonlinear oscillatory mode appears due to the negative differential mobility effect, which is the unique feature of wurtzite InN aroused by its strong nonparabolicity of the Γ₁ valley. The appearance of different nonlinear oscillatory modes, including periodic and chaotic states, is attributed to the competition between the self-sustained oscillation and the external driving oscillation. The transitions between the periodic and chaotic states are carefully investigated using chaos-detecting methods, such as the bifurcation diagram, the Fourier spectrum and the first return map. The resulting bifurcation diagram displays an interesting and complex transition picture with the driving amplitude as the control parameter.     

Magnetization-induced third-harmonic generation in nanostructures and thin films

This paper reports on the results of research into low-dimensional magnetic structures that have been intensively studied over previous decades due to the discovery of novel effects that are exhibited by these structures but not observed in bulk magnetic materials. A nonlinear optical analog of the magnetooptical Kerr effect is revealed in the optical third-harmonic generation in thin magnetic metallic films and nanogranular structures. It is shown that the magnetic nonlinear optical Kerr effect observed in the third harmonic exceeds the magnetooptical analog by more than one order of magnitude.     

Nonlinear generation of vorticity in thin smectic films

The energy levels of the fermions bound to the vortex are considered for vortices in the superfluid/superconducting systems that contain the symmetry protected plane of zeroes in the gap function in bulk. The Caroli–de Gennes–Matricon branches with different approach zero energy level at p_z → 0. The density of states of the bound fermions diverges at zero energy giving rise to the \(\sqrt \Omega \) dependence of the density of states in the polar phase of superfluid ³He rotating with the angular velocity Ω and to the \(\sqrt B \) dependence of the density of states for superconductors in the (d_xz + id_yz)-wave pairing state.     

Electrodynamic properties of lead Zirconate-Titanate thin films in the terahertz frequency range

The transmission/reflection spectra of bilayer structures consisting of thin amorphous and polycrystalline Pb(Zr_0.52Ti_0.48)O₃ ferroelectric films deposited on dielectric substrates of magnesium oxide MgO and sapphire α-Al₂O₃ were measured in the frequency range of 5–4000 cm^?1. Based on these spectra and using the dispersion analysis method, the spectra of complex dielectric permittivity ?*(ν) and dynamic conductivity σ′(ν) of the films were simulated, the electrodynamic parameters of the films were determined, and the dielectric dispersion responsible for the formation of static permittivity was found.     

Study of terahertz radiation generated by optical rectification on thin gold films

Emission of terahertz (THz) radiation as a result of optical rectification of intense femtosecond laser pulses on thin gold films has been studied by time-domain THz spectroscopy. The THz amplitude was measured as a function of film thickness and incidence angle. The experiments reveal that the emitted THz field is suppressed for a thickness below 100 nm, which gives evidence of the nonlocal character of the response. The variation of incidence angle allows us to estimate the components of susceptibility tensor chi2ijk. For thicker films and near grazing incidence, the emitted THz field attains a peak value of 4 kV/cm.     

Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy

Using time-domain terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare quasiparticle recombination rate, the Cooper pair-breaking rate and the electron-phonon coupling constant, λ=1.1±0.1, which is in excellent agreement with theoretical estimates.     

Percolation-enhanced generation of terahertz pulses by optical rectification on ultrathin gold films

Emission of pulses of electromagnetic radiation in the terahertz range is observed when ultrathin gold films on glass are illuminated with femtosecond near-IR laser pulses. A distinct maximum is observed in the emitted terahertz amplitude from films of average thickness just above the percolation threshold. Our measurements suggest that the emission is through a second-order nonlinear optical rectification process, enhanced by the excitation of localized surface plasmon hot spots on the percolated metal film.     

InN薄膜的氧化特性研究

研究了InN薄膜在不同氧气氛中的氧化特性. 研究表明，在400 ℃以下，InN薄膜很难被氧化，而金属In很容易被氧化. 因此富In的InN薄膜的氧化在400 ℃以下主要是金属In的氧化，在400 ℃以上为金属In和InN的同时被氧化. 在400 ℃以上的氧化过程中，InN的表观氧化速率非常慢，这可能和InN的高温分解有关. InN的湿氧和干氧氧化结果说明湿氧氧化速率比干氧快. 关键词： InN 氧化铟 氧化 X射线衍射     

Correlation between structural and electrical properties of InN thin films prepared by molecular beam epitaxy

The strain-relaxation phenomena and the formation of a dislocation network in 2H-InN epilayers during molecular beam epitaxy are reported. The proposed growth model emphasizes the dominant role of the coalescence process in the formation of a dislocation network in 2H-InN. Edge type threading dislocations and dislocations of mixed character have been found to be the dominating defects in wurtzite InN layers. It is demonstrated that these dislocations are active suppliers of electrons and an exponential decay of their density with the thickness implies a corresponding decay in the carrier density. Room temperature mobility in excess of 1500 cm² V ⁻¹ s⁻¹ was obtained for 800 nm thick InN layers with dislocation densities of 3×10⁹ cm⁻².     

Dynamically phase-matched terahertz generation

We present the generation of intense terahertz pulses by optical rectification of 780 nm pulses in a large area gallium phosphide crystal. The velocity mismatch between optical and terahertz pulses thereby limits the bandwidth of the terahertz pulses. We show that this limitation can be overcome by a dynamic modification of the refractive index of the gallium phosphide crystal through generation of hot phonons. This is confirmed by excellent agreement between experimental results and model calculations.     

Resonant surface enhanced Raman scattering by ultra thin Langmuir-Blodgett polydiacetylene polymer films

Using resonant Raman scattering and surface enhanced Raman scattering techniques, changes in the structural and electronic properties of Langmuir-Blodgett (L-B) polydiacetylene films were observed as film thicknesses were increased from one monolayer (or one bilayer) to several bilayers. The L-B films, starting with a single monolayer (or one bilayer) in a disordered “red” phase, were found to change into a mixed phase (ordered “blue” and disordered “red”) as one or more additional bilayers were deposited. This is the first observation of a “disorder to order” transformation in a L-B film. The observed effect is attributed to the ordering brought about by interactions between the initial and subsequent L-B PDA bilayers.