Deposition of ZnO Films on Freestanding CVD Thick Diamond Films

For ZnO/diamond structured surface acoustic wave （SAW） filters, performance is sensitively dependent on the quality of the ZnO films. In this paper, we prepare highly-oriented and fine grained polycrystalline ZnO thin films with excellent surface smoothness on the smooth nucleation surfaces of freestanding CVD diamond films by metal organic chemical vapour deposition （MOCVD）. The properties of the ZnO films are characterized by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, and photoluminescence （PL） spectrum. The influences of the deposition conditions on the quality of ZnO films are discussed briefly. ZnO/freestanding thick-diamond-film layered SAW devices with high response frequencies are expected to be developed.

P-BN/n-Si Heterojunction Prepared by Beryllium ion Implantation

A boron nitride （BN）/silicon p-n heterojunction is fabricated by implanting beryllium （Be） ions into the BN films deposited by rf sputtering on n-type Si （111） substrates. The FTIR observations indicate that the films deposited have a mixed phase composition of 8p^2 - and sp^3 -hybridized BN. Considering the thickness of the BN layer, the ion implantation is conducted at an ion energy of 100keV with the dose of 5×10^15 cm^-2. After annealing at a high temperature, the surface resistance of the BN film decreases significantly by 6 orders down to 1.2×10^5Ω. Space-charge-limited current characteristic, which indicates the existence of shallow traps in the film, is observed. Current-voltage measurements across the BN film and the Si substrate reveal a clear rectification feature, demonstrating the achievement of p-type doping of BN films by Be ion implantation.

Synthesis and PL Properties of ZnSe Nanowires with Zincblende and Wurtzite Structures

Single crystalline ZnSe nanowires with both zincblende and wurtzite structures have been synthesized via a chemical vapour deposition method under different growth conditions. The nanowires are usually 50-80nm in diameter, and several tens of microns in length. Room-temperature photoluminescence spectra from zincblende and wurtzite ZnSe nanowires show a broad luminescence band peaked at around 2. 71 e V and a deep level emission band peaked at around 2.00 eV, respectively. Effects of post-growth annealing on the photoluminescence of these nanowires have been investigated. Strong room-temperature band-edge emission could be obtained from the annealed zincblende ZnSe nanowires.

Microstructure Modification of Silicon Nanograins Embedded in Silicon Nitride Thin Films

Microstructure modification of silicon nanograins embedded in silicon nitride films by introducing hydrogen reactant in the plasma enhanced chemical vapour deposition process and their optical properties are analysed using Raman scattering, optical absorption and photoluminescence （PL） measurements. It is found that the silicon nanograins embedded in the silicon nitride （SiNx） matrix are transformed into silicon nanocrystals and the optical properties of the films change dramatically when introducing H2 into Ar-sustained plasma. The optical absorption coefficient of the films within the band gap decreases by about one order of magnitude and the PL intensity increases significantly, compared with that without hydrogen introduction. These results suggest that atomic hydrogen in the plasma has the function of crystallizing silicon nanograins and passivating defects at the silicon nanograins/SiNx interface.

Effect of F- and CH-Doped on Dielectric Properties of SiCOH Films Deposited by Decamethylcyclopentasiloxane Electron Cyclotron Resonance Plasma

We investigate the effect of CH-doped and F-doped on dielectric properties of SiCOH films deposited by de- camethylcyclopentasiloxane （DMCPS） electron cyclotron resonance plasma. The dielectric constant k is closely related to the configurations of films. For the films deposited only using DMCPS, the minimum k is as low as 2.88. By adding CH4 in the precursor, the k value can be reduced to 2.45 due to the film density decreasing by incorporating large size CHx groups. By adding CHF3 in the precursor, the k value can also be reduced to 2.48 due to the incorporation of the weak-polarization F atom. Thus the dielectric constant for SiCOH films depends on not only the film density but also the polarization of atoms. By increasing the film density or by reducing the polarization of atoms under the condition of a lower film density, the low dielectric constant SiCOH films can be obtained.

Structural, Morphology and Optical Properties of Epitaxial ZnO Films Grown on Al2O3 by MOCVD

Epitaxial ZnO films are grown on Al2O3 （0001） by the MOCVD method. These films are high quality wurtzite crystals with （0001） orientation. Big hexagonal crystallites （diameter from several decades to 100 μm） are found on the surface. Inside these crystallites, a stronger luminescence is observed compared with the plain area. Transmission electronic microscopy reveals that the film is thicker inside the hexagonal crystallites than the plain area, and some crystallites are not connected with each other and are slightly rotated with respect to their neighbours.

MOCVD Growth and Characterization of Epitaxial AlxGa1-xN Films

We study the growth of AlxGa1-x N epilayers on （0001） sapphire by low-pressure MOCVD, using a lowtemperature AIN buffer. By varying the input flow rates of trimethylgallium （TMGa）, we obtain crack-free AlGaN films in the whole range of composition. A linear relationship between gas and solid Al content is observed. The structural properties of the layers （x =0- 1） are investigated by x-ray diffraction, atomic force microscopy （AFM） and scanning electron microscopy （SEM）. It is found that a two-direction growth appears along the c-axis and the （1011） directions for x ≥ 0.45. From the results of Raman spectroscopy, we suggest that the compressive stain and the lack of mobility orAl adatoms can induce the formation of （1011） grains.

Electroluminescence of an n-ZnO/p-GaN Heterojunction under Forward and Reverse Biases

Electroluminescent characteristics of n-ZnO/p-GaN heterojunctions under forward and reverse biases are studied. Emissions at 389nm and 57Ohm are observed under forward bias. An unusual emission at 390ram appears under reverse bias, and is attributed to the recombination in the p-GaN side of the heterojunction. The yellow emission peaked at 57Ohm is suppressed under reverse bias. The light intensity exponentially depends on the reverse current. The emission under reverse bias is correlated to tunnelling carrier transport in the heterostructure. Our results also support that the well-known yellow band of GaN comes from the transitions between some near-conduction-band-edge states and deep localized acceptor states.

Synthesis of Boron-Rich Cubic B（CxN1-x） Compounds

B2CN precursor is prepared by a mechanical vibration-milling process using amorphous boron, graphite and h-BN powders with mole ratio of 1：1：1. A mixture of precursor and Ca3B2N4 catalyst is treated under high pressure and high temperature. A boron rich cubic B（CxN1-x） phase is obtained after removing the catalyst by acid treatment. The average C content of the boron-rich cubic phase is about 6 at.% detected by energy-dispersive x-ray analysis spectroscopy. It is found that the highest carbon content in the cubic phase is as large as 16 at.%.

Elimination of Crystallographic Wing Tilt of Canti-Bridged Epitaxial Laterally Overgrown GaN Films by Optimizing Growth Procedure

Canti-bridged epitaxial lateral overgrowth （CBELO） of GaN is performed by metalorganic chemical vapour deposition （MOCVD） on maskless V-grooved sapphire substrates prepared by wet chemical etching with different mesa widths. The wing tilt usually observed in ELO is not found in the CBELO GaN with wide mesa widths, while it can be detected obviously in the GaN with narrow mesa widths. The wing tilt of CBELO GaN grown on a grooved sapphire substrate with narrow mesa can be controlled by adjusting the thickness of the nucleation layer. The dependence of the wing tilt on the nucleation layer thickness is studied. Cross-sectional scanning electron microscopy is used to characterize the geometry of the wing regions, and double crystal x-ray diffraction is used to analyse the structural characteristics and to measure the magnitude of the crystalline wing tilt. It is found that the crystalline wing tilt can be eliminated completely by first growth of a thin nucleation GaN layer then the CBELO GaN. Possible reason and the origin of the wing tilt in CBELO GaN films are also discussed.

Characteristics of High In-Content InGaN Alloys Grown by MOCVD

InN and In0.46 Ca0.54N films are grown on sapphire with a CaN buffer by metalorganic chemical vapour deposition （MOCVD）. Both high resolution x-ray diffraction and high resolution transmission electron microscopy results reveal that these films have a hexagonal structure of single crystal. The thin InN film has a high mobility of 4 75 cm^2V^-1s^-1 and that oflno.46 Gao.54N is 163 cm^2 V^-1s^-1. Room-temperat ure photoluminescence measurement of the InN film shows a peak at 0.72eV, confirming that a high quality InN film is fabricated for applications to full spectrum solar cells.

Comparison of Properties of Pt/PZT/Pt and Ru/PZT/Pt Ferroelectric Capacitors

Pb（Zr0.4Ti0.6）O3 film prepared by sol-gel spin coating on a Pt/Ti/SiO2/Si substrate is applied to ferroelectric capacitors with Pt or Ru as the top electrode. For the Pt/PZT/Pt and Ru/PZT/Pt ferroelectric capacitors, although with the same ferroelectric film, different top electrode materials incur different properties of PZT capacitors, such as fatigue, leakage, remanent and saturated polarization, except the similar crystal orientations of the PZT film. After 10^10 switch cycles, the remanent polarizations of the Ru/PZT/Pt and Pt/PZT/Pt capacitors decrease to 70% and 84%, respectively. The leakage current density of the latter increases obviously at positive bias after 108 switch cycles, compared with the former. Different materials for the top electrode bring different conditions at the PZT/top electrode interface. The influence of oxygen-vacancy concentration at the PZT/electrode interface and the influence of oxides of the electrode material at the PZT/electrode interface to charge injection can explain the difference of properties of the PZT capacitors with Pt or Ru as the top electrodes.

Reduction of Dislocations in GaN Epilayer Grown on Si （111） Substrates using a GaN Intermedial Layer

GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AIN/Si（111） substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional （3D） mode to the 2I） one occurs during the GaN epilayer growth when a higher growth pressure is used during the preceding GaN intermedial layer growth, and an improvement of the crystalline quality of GaN epilayer will be made. Combining the in situ reflectivity and transmission electron microscopy （TEM） measurements, it is suggested that the lateral growth at the transition of growth mode is favourable for bending of dislocation lines, thus reducing the density of threading dislocations in the epilayer.

Influence of Positive Bias on Electrical Properties of Undoped Nanocrystalline Diamond Films

By means of electron assisted hot filament chemical vapour deposition technology, nanocrystalline diamond films are deposited on polished n-（100）Si wafer surface at I kPa gas pressure. The deposited films are characterized with a Raman spectrometer, atomic force microscope, semiconductor characterization system and Hall effect measurement system. The results show that, when bias current is larger than 2 A, sheet hole concentration can increase to a value greater than 1013 cm-2 and undoped nanocrystalline diamond films with a p-type semiconducting characteristic form. Heterojunction between n-Si substrate and the nanocrystalline diamond films deposited with 2 A and 6 A bias current has an evident junction effect. Hole formation mechanisms in the films are discussed.

Characterization of Undoped and Cu-Doped ZnO Thin Films Deposited on Glass Substrates by Spray Pyrolysis

Undoped and copper doped zinc oxide （ZnO） thin films have been prepared on glass substrates by spray pyrolysis technique. The films were doped with copper using the direct method by addition of a copper salt （CuCl2） in the spray solution of ZnO. Variation of structural, electrical, optical and thermoluminescence （TL） properties with doping concentrations is investigated in detail.

Effect of Pretreatment of TaN Substrates on Atomic Layer Deposition Growth of Ru Thin Films

The polycrystalline ruthenium films are grown on TaN substrates by atomic layer deposition （ALD） using bis（cyclopentadienyl） ruthenium [RuCp2] and oxygen as ruthenium precursor and reactant respectively at a deposition temperature of 330℃. The low-energy Ar ion bombardment and Ru pre-deposition are performed to the underlying TaN substrates before ALD process in order to improve the Ru nucleation. X-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy are carried out to characterize the properties of ALD Ru films. The results show that the nucleation density of Ru films with Ar^＋ bombardment to the underlying TaN substrates is much higher than that of the ones without any pretreatment. The possible reasons are discussed.

A Comparison of GaN Epilayers with Multiple Buffer Layers and with a Single Buffer Layer Grown on Si（111） Studied by HRXRD and RBS/Channeling

Two hexagonal GaN epilayers （samples A and B） with multiple buffer layers and single buffer layer are grown on Si （111） by metal-organic vapour phase epitaxy （MOVPE）. From the results of Rutherford backscattering （RBS）/channeling and high resolution x-ray diffraction （HRXRD）, we obtain the lattice constant （a and c） of two GaN epilayers （aA = 0.3190 nm, cA = 0.5184 nm and aB = 0.3192 nm, CB = 0.5179 nm）, the crystal quality of two GaN epilayers （ ХminA=4.87%, ХminB =7.35% along 〈1-↑213〉 axis） and the tetragonal distortion eT of the two samples along depth （sample A is nearly fully relaxed, sample B is not relaxed enough）. Comparing the results with the two samples, it is indicated that sample A with multiple buffer layers have better crystal quality than sample B with a single buffer layer, and it is a good way to grow GaN epilayer on Si （111） substrates using multiple buffer layers to improve crystal quality and to reduce lattice mismatch.

Tetragonal Distortion of GaN Epilayer with Multiple Buffer Layers on Si （111） Studied by RBS/Channelling and HRXRD

Rutherford backscattering （RBS）/channelling and high resolution x-ray diffraction （HRXRD） have been used to characterize the tetragonal distortion of a GaN epilayer with four Alx Ga1-xN and single AIN buffer layers grown on a Si （111） substrate by metal-organic vapour phase epitaxy （MOVPE）. The results show that a 1000nm GaN epilayer with a perfect crystal quality （Xmin = 1.54%） can be grown on the Si （111） substrate in virtue of multiple buffer layers. Using the RBS/channelling angular scan around an off-normal （1213） axis in the （1010） plane and the conventional HRXRD θ - 20 scans normal to GaN （0002） and （1122） planes at the 0° and 180° azimuth angles, the tetragonal distortion eT, which is caused by the elastic strain in the epilayer and different buffer layers, can be obtained respectively. The two experiments are testified at one result, the tetragonal distortion of GaN epilayer is nearly to a fully relaxed （eT = 0）.

Effect of Bias on Content of GeC in Ge1-xCx Films

Ge1-x Cx films with GeC content up to 11.6% can be prepared by using a medium frequency magnetron sputtering technique in our study. X-ray photoelectron analysis for these Ge1-x Cx films shows that the Ge1-x Cx films consist of C, Ge, GeC and GeOy. The content of GeC increases from 10.7% at 0 V to 11.6% at 250 V, and decreases to 9.6% at 350 V, and then increases again to 10.4% at 450 V. The Raman analysis confirms the result of XPS for checking GeC in the deposited Ge1-x Cx films. The related mechanism is discussed.