Xiangyun Han

A new comprehensive model for the pyroelectric property of 0-3 ferroelectric composites

A new comprehensive model has been developed for the pyroelectric activity of 0-3 ferroelectric composites which includes additional contributions from the electrical conductivity of the constituents and the frequency of measurement when the secondary pyroelectric effect resulting from the coupled thermoelectroelastic behaviour is considered. The boundary conditions are obtained in terms of the Laplace equation and Maxwells equations. The analytical expressions have been derived for primary and secondary pyroelectric coefficients. The effects of the electrical conductivity of the matrix σm and the measuring frequency f on the pyroelectric property have been investigated in detail. Possible methods for improving the pyroelectric effect are also discussed. Our model can reflect comprehensively the pyroelectric property of the material and shows reasonably good agreement with experimental data.

Nonpolar a-plane ZnO films grown on GaN/sapphire templates with SiNx interlayer by pulsed laser deposition

Nonpolar a-plane ZnO films were deposited for the first time on nearly lattice-matched a-plane GaN templates using an in situ SiNx interlayer by the pulsed laser deposition method. The symmetric and asymmetric reciprocal space mappings reveal the broadening effects of the reciprocal lattice points and the residual biaxial in-plane tensile strain of a-plane ZnO to be 0.335% and 0.055% along the [0 0 0 1] c-axis and p-axis, respectively. The photoluminescence spectrum at 85 K is dominated by neutral donor-bound excitons and free-electron-to-bound (e-A0) emissions; relatively intense LO-phonon replicas of (e-A0) have also been observed in a-plane ZnO. Temperature-dependent PL spectra have also been discussed to identify the origin of the emission peaks. Up to fourth A1(LO) phonon mode can be observed to be enhanced significantly from the resonant Raman spectrum.

Optical and electrical characterization of α-InGaZnO thin film fabricated by pulsed laser deposition for thin film transistor applications

Highly transparent and amorphous InGaZnO thin films with high mobility were deposited on fused silica by pulsed laser deposition. The films remained amorphous after annealing at 700 °C and had bandgaps in the range 3.50–3.62 eV. The film deposited at 5 Pa and room temperature exhibits a Hall mobility of 54 cm2 V−1 s−1. An α-InGaZnO thin film transistor with high-k Ba0.6Sr0.4TiO3 as a dielectric layer and operating in enhanced mode with a saturation mobility of 5.8 cm2 V−1 s−1 and on/off ratio of 2 × 105 is demonstrated.

Effect of electrical conductivity on the polarization behaviour and pyroelectric, piezoelectric property prediction of 0–3 ferroelectric composites

We have investigated the effect of electrical conductivity of the constituents on the poling behaviour of the ceramic inclusions in 0–3 ferroelectric composites which comprise a dilute suspension of spherical particles uniformly distributed in the matrix material. A new model for the pyroelectric and piezoelectric properties in terms of the poling conditions (poling field and poling time) has been developed to include electrical conductivity. Simulated results show that conductivity plays an important role in the poling process. Properly increasing the conductivity of the matrix σm can enhance the polarization in the ceramic inclusion of the composite Pi, thereby making the poling of the composite more efficient. In contrast, higher conductivity of the ceramic inclusion σi results in lower polarization Pi, which is unfavourable to the poling of the composite. These results provide insights into the observed behaviour of 0–3 composites. The model predicts the pyroelectric and piezoelectric properties under different poling conditions, which agree well with the corresponding experimental data.

Epitaxial growth a-plane ZnO films on a-GaN/r-Al2O3 templates

In this work, we have grown a-plane ZnO films on a-plane GaN/r-sapphire templates by pulsed laser deposition. The aplane GaN of the templates is aimed to mitigate the large lattice mismatch between ZnO and sapphire, and was grown by metal organic chemical vapor deposition. The grown a-plane ZnO films have been analyzed by various techniques such as high resolution X-ray diffraction, photoluminescence. It shows that high quality a-plane ZnO films have been achieved by our growth method.

High quality a-plane GaN layers grown by pulsed atomic-layer epitaxy on r-plane sapphire substrates

In this work, pulsed atomic-layer epitaxy (PALE) technique has been used to grow a-plane GaN films on r-plane sapphire substrates. During growth, the supply of N atoms was alternatively turned on and off while Ga atoms were continuously supplied with a constant flow rate. By optimizing the on/off periods of N source at 20/10 secs, pit-free GaN films have been obtained with significantly reduced full width at half maximum of X-ray rocking curve and brighter characteristic emission of stacking faults, as compared to the case using conventional metal-organic chemicalvapor deposition. The improved epitaxy quality and optical properties in PALE is due to the enhanced the Ga-adatom surface migration and improved the lateral-growth rate, which results in larger grain size and longer stacking faults.