Woei-Tyng Lin

Effects of RF power on the structural, optical and electrical properties of Al-doped zinc oxide films

Abstract In this study, we discussed the effects of growth parameters on the structural and optical properties of Al-doped zinc oxide (AZO) deposited at room temperature by radio-frequency magnetron sputtering. The AZO films have been characterized in detail using X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, Hall-effect measurement system and UV–visible spectrophotometer. It was found that the morphological, structural, electrical and optical properties of AZO films are greatly dependent on sputtering power. Collision between sputter species and surface morphology play important roles in optoelectrical properties of AZO films. According to our experimental results, the AZO films can be used in versatile devices to meet various requirements.

Observation of unusual optical transitions in thin-film Cu(In,Ga)Se 2 solar cells

In this paper, we examine photoluminescence spectra of Cu(In,Ga)Se(2) (CIGS) via temperature-dependent and power-dependent photoluminescence (PL). Donor-acceptor pair (DAP) transition, near-band-edge transition were identified by their activation energies. S-shaped displacement of peak position was observed and was attributed to carrier confinement caused by potential fluctuation. This coincides well with the obtained activation energy at low temperature. We also present a model for transition from V(Se) to V(In) and to V(Cu) which illustrates competing mechanisms between DAPs recombinations.

Indium nitride epilayer prepared by UHV-plasma-assisted metalorganic molecule beam epitaxy

Indium nitride films grown at various growth temperatures were prepared on GaN buffer layers using self-designed plasma-assisted metal-organic molecular beam epitaxy. The influence of substrate temperature on film crystallinity, surface morphology, optical, and electrical properties was studied using x-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), UV/VIS/NIR spectrophotometer, and Hall measurement. The results show that the InN films grown on the GaN template at 500 oC are of good quality, and the full width at half maximum of InN(0002) ω-scan is around 1000 arc sec. The SEM images revealed that the average growth rate is 1.1 μm/h, which is comparable to the conventional epitaxial techniques. These results indicate that the electronic properties and crystalline quality can be significantly improved by optimizing the growth temperature.

Structural and morphological evolution of gallium nitride nanorods grown by chemical beam epitaxy

The morphological and structural evolution is presented for GaN nanorods grown by chemical beam epitaxy on (0001) Al2O3 substrates. Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and temperature-dependent photoluminescence measurements. While increasing the growth temperature and the flow rate of radio-frequency nitrogen radical, the three-dimensional growth mode will be enhanced to form one-dimensional nanostructures. The high density of well-aligned nanorods with a diameter of 30–50nm formed uniformly over the entire sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the self-assembled GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. Particularly, the “S-shape” behavior with localization of ∼10meV observed in the temperature-dependent photoluminescence might be ascribed to the fluctuation in crystallographic defects and compo...

Study of InN epitaxial films and nanorods grown on GaN template by RF-MOMBE.

This paper reports on high-quality InN materials prepared on a GaN template using radio-frequency metalorganic molecular beam epitaxy. We also discuss the structural and electro-optical properties of InN nanorods/films. The X-ray diffraction peaks of InN(0002) and InN(0004) were identified from their spectra, indicating that the (0001)-oriented hexagonal InN was epitaxially grown on the GaN template. Scanning electron microscopic images of the surface morphology revealed a two-dimensional growth at a rate of approximately 0.85 μm/h. Cross-sectional transmission electron microscopy images identified a sharp InN/GaN interface and a clear epitaxial orientation relationship of [0001]InN // [0001]GaN and (2¯110)InN // (2¯110)GaN. The optical properties of wurtzite InN nanorods were determined according to the photoluminescence, revealing a band gap of 0.77 eV.

Characterization of large area Cu(In,Ga)Se 2 nanotip arrays via photoluminescence

In this study, photoluminescence (PL) measurements were used to characterized Cu(In,Ga)Se2 nanotip arrays (CIGS NTRs). Large area CIGS NTRs were yielded by using one step Ar+ milling process without template. Formation mechanism of NTRs is due to a highly anisotropic milling effect of the quaternary components compound. In both CIGS thin films with and without NTRs, saturation effects of Donor-Acceptor Pair (DAP) had been observed while excitation power dependence PL measurements. Comparing with thin film CIGS without NTRs, it has revealed that the concentration DAP had been changed after formation of CIGS NTRs and had enhanced its carrier density of the p-type semiconductor.

Effect of growth parameters on surface morphology evolution of MOMBE-grown InN

This work reports on the effects of growth temperature, TMIn flow rate and AlN buffer on InN thin films grown by RF-MOMBE epitaxy system. Structural and surface morphology were analyzed by XRD, FE-SEM, AFM and TEM, respectively. Electrical properties were performed by Hall measurement. While the growth temperature is at 500 oC, InN grown directly on sapphire substrate preferred two-dimensional (2D) rather than island (3D) growth. However, the thickness of InN with smooth surface was limited at 50 nm due to residual stress caused by lattice mismatch. Moreover, In segregation was found under high TMIn flow rate condition. With the assistance of low-temperature grown intermediate AlN buffer layer, we can effectively improve the structural and electrical properties of InN. Experimental results indicate that the growth parameters are essential for engineering the growth of indium nitride.

Fabrication and characterization of nano-structured aluminum-doped zinc oxide films

Nanostructured ZnO samples on Si(100) and glass substrates have been synthesized by simple chemical solution method with post-thermal treatments. UV-vis spectrum, Hall measurement, and photoluminescence and scanning electron microscopy (SEM) have been used to characterize nanostructured ZnO thin films at various annealing temperatures. Post-thermal treatment does not only modify the surface morphology but also the intensity ratio of near-band-edge to green emission of ZnO samples. Meanwhile, the ZnO samples exhibited free exciton and very sharp exciton emissions at low temperatures. The average transmittance of nanostructured ZnO in the visible range was above 80 %, and optical band gap increased as increasing the annealing temperature, which might be explained by the Burstein-Moss effect. Experimental results reveal that post-thermal treatment play a key role in the fabrication of ZnO-based photonic devices.

The quantum confinement effect of InGaN/GaN nanorods by photoelectrochemical oxidation

In this study, the nanorods of 100–150nm diameter on an InGaN/GaN multi quantum well (MQW) structure were fabricated using self-assembled nickel metal nanomasks and inductively coupled plasma reactive ion etching. The photoelectron- chemical (PEC) methods were applied to oxidate the InGaN/GaN MQWs nanorods. After 5V/80min oxidation, the measured PL from the embedded InGaN/GaN MQWs shows an energy shift of 30meV and a smaller QCSE, which are caused by quantum confinement effect and the strain relaxation of MQWs. The blue shift range increased with decreasing MQWs diameter.

Characterization of InN films grown by plasma-assisted MOMBE

In this paper, we report the growth of InN films on sapphire substrate by RF- MOMBE. GaN buffer layer was used to lower the lattice mismatch between InN and sapphire. XRD patterns indicated that the InN films were grown epitaxially along the c-axis direction. In addition, increasing III/V ratio and growth temperature improve the quality of the InN films as well. However, In droplet will appear on the sample surface under the condition with high III/V ratio. Under optimal growth condition, electron mobility was improved from 100 cm2/V-s to 366 cm2/V-,. Experimental results showed that III/V ratio and growth temperature play important roles in the InN epitaxial growth.