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1.
ACS Appl Mater Interfaces ; 11(19): 17563-17569, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-31026139

RESUMO

Aluminum-gallium oxide (AGO) thin films with wide bandgaps of greater than 5.0 eV were grown using pulsed laser deposition. As evidenced by X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy, the oxygen chamber pressure considerably affected the lattice deformation in the AGO materials. Under high oxygen pressure, the lattice deformation reduced the d-spacing of the AGO(-201) plane. In the measured transmittance spectra of the AGO films, this narrowing of the d-spacing in the main plane manifested as a high-energy shift of the absorption edge. The AGO films were then installed as the active layers in the metal-semiconductor-metal photodetectors (PDs). The lattice deformation was observed to enhance the photocurrent and reduce the dark current of the device. The responsivity was 20.7 times higher in the lattice-deformed AGO-based PD sample than that in the nondeformed sample. It appeared that the lattice deformation induced the separation of the piezopotential, improving the efficiency of the photogenerated carrier recombination and, consequently, shortening the decay time of the photodetector.

2.
Nanoscale Res Lett ; 14(1): 83, 2019 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-30847661

RESUMO

In this work, hafnium oxide (HfO2) thin films are deposited on p-type Si substrates by remote plasma atomic layer deposition on p-type Si at 250 °C, followed by a rapid thermal annealing in nitrogen. Effect of post-annealing temperature on the crystallization of HfO2 films and HfO2/Si interfaces is investigated. The crystallization of the HfO2 films and HfO2/Si interface is studied by field emission transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy. The experimental results show that during annealing, the oxygen diffuse from HfO2 to Si interface. For annealing temperature below 400 °C, the HfO2 film and interfacial layer are amorphous, and the latter consists of HfO2 and silicon dioxide (SiO2). At annealing temperature of 450-550 °C, the HfO2 film become multiphase polycrystalline, and a crystalline SiO2 is found at the interface. Finally, at annealing temperature beyond 550 °C, the HfO2 film is dominated by single-phase polycrystalline, and the interfacial layer is completely transformed to crystalline SiO2.

3.
Materials (Basel) ; 11(11)2018 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-30355986

RESUMO

This study investigates the thermal decomposition behavior of GaN-based epilayers on patterned sapphire substrates (GaN-epi/PSSs) in a quartz furnace tube under a hydrogen atmosphere. The GaN-epi/PSS was decomposed under different hydrogen flow rates at 1200 °C, confirming that the hydrogen flow rate influences the decomposition reaction of the GaN-based epilayer. The GaN was completely removed and the thermal decomposition process yielded gallium oxyhydroxide (GaO2H) nanostructures. When observed by transmission electron microscopy (TEM), the GaO2H nanostructures appeared as aggregates of many nanograins sized 2⁻5 nm. The orientation relationship, microstructure, and formation mechanism of the GaO2H nanostructures were also investigated.

4.
Nanomaterials (Basel) ; 8(9)2018 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-30201865

RESUMO

In this paper, we report the epitaxial growth and material characteristics of AlGaN (Al mole fraction of 10%) on an AlN/nanopatterned sapphire substrate (NPSS) template by hydride vapor phase epitaxy (HVPE). The crystalline quality, surface morphology, microstructure, and stress state of the AlGaN/AlN/NPSS epilayers were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The results indicate that the crystal quality of the AlGaN film could be improved when grown on the AlN/NPSS template. The screw threading dislocation (TD) density was reduced to 1.4 × 108 cm-2 for the AlGaN epilayer grown on the AlN/NPSS template, which was lower than that of the sample grown on a flat c-plane sapphire substrate (6.3 × 108 cm-2). As examined by XRD measurements, the biaxial tensile stress of the AlGaN film was significantly reduced from 1,187 MPa (on AlN/NPSS) to 38.41 MPa (on flat c-plane sapphire). In particular, an increase of the Al content in the overgrown AlGaN layer was confirmed by the TEM observation. This could be due to the relaxation of the in-plane stress through the AlGaN and AlN/NPSS template interface.

5.
Sci Rep ; 8(1): 9255, 2018 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-29915301

RESUMO

To acquire device-quality TiOx films usually needs high-temperature growth or additional post-thermal treatment. However, both processes make it very difficult to form the p-type TiOx even under oxygen-poor growth condition. With the aid of high energy generated by high power impulse magnetron sputtering (HIPIMS), a highly stable p-type TiOx film with good quality can be achieved. In this research, by varying the oxygen flow rate, p-type γ-TiO and n-type TiO2 films were both prepared by HIPIMS. Furthermore, p- and n-type thin film transistors employing γ-TiO and TiO2 as channel layers possess the field-effect carrier mobilities of 0.2 and 0.7 cm2/Vs, while their on/off current ratios are 1.7 × 104 and 2.5 × 105, respectively. The first presented p-type γ-TiO TFT is a major breakthrough for fabricating the TiOx-based p-n combinational devices. Additionally, our work also confirms HIPIMS offers the possibility of growing both p- and n-type conductive oxides, significantly expanding the practical usage of this technique.

6.
Sci Rep ; 8(1): 4865, 2018 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-29559658

RESUMO

In conventional emitting devices, the mobility of electron is much higher than that of hole, which increases the non-recombination rate. To generate slow electrons, we demonstrate an electron retarding n-electrode (ERN) on the n-GaN layer of InGaN blue light emitting diode (LED), making more efficient radiation emission. Transparent conductive oxides are estimated to be more suitable for ERN materials. However, for ERN materials used in InGaN LEDs, three requirements should be satisfied, i.e., Ohmic contact to n-GaN, dilute magnetic doping, and good electrical conductivity. The pulsed-laser deposited cobalt-doped ZnO film prepared at 400 °C was chosen as the ERN. The electron retarding of 120-nm-thick ERN/n-GaN reached 19.9% compared to the n-GaN. The output powers (@350 mA) of LEDs with and without the ERN were 246.7 and 212.9 mW, while their wall-plug efficiencies were 18.2% and 15.1%, respectively. Moreover, owing to the efficient filling of electrons in the quantum wells by inserting the ERN, the bandgap of quantum wells was enlarged, inducing the blue-shift in the emission wavelength of LED. The slow electron generated from the ERN technique paves the way to solve the problem of large difference between electron and hole velocities and improve the optoelectronic performance of emitting devices.

7.
Sci Rep ; 7(1): 14251, 2017 10 27.
Artigo em Inglês | MEDLINE | ID: mdl-29079822

RESUMO

A novel fabrication method for single crystalline ZnO nanorods by pulsed laser deposition (PLD) using a chemical-bath-deposited ZnS seed layer is proposed. For the substrate temperature (Ts) lower than 700 °C, the PLD-ZnO showed a polycrystalline phase and film-type morphology, resulting from the ZnS seed layer with a cubic phase. However, the ZnS film became a sacrifical layer and single crystalline ZnO(002) nanorods can be achieved at Ts of 900 °C, where ZnS was decomposed to zinc metals and sulfur fumes. The transformation from ZnO film to nanorod microstructure was demonstrated with the change of ZnS layer into Zn grains. Enhanced performance of the metal-semiconductor-metal photodetectors were fabricated with ZnO/ZnS samples grown at Ts of 500, 700, and 900 °C. The responsivities (@1 V and 370 nm) of these three devices were 1.71, 6.35, and 98.67 A/W, while their UV-to-visible discrimination ratios were 7.2, 16.5, and 439.1, respectively. Obviously, a higher light-capturing efficiency was obtained in the 900 °C-grown ZnO/ZnS device owing to its one-dimensional nanostructure with high crystal quality. The results indicate PLD combined with a sacrifical nanostructure is a promising method for obtaining high-quality ZnO nanorods, which paves the way for the fabrication of high performance ZnO-based devices.

8.
Materials (Basel) ; 9(11)2016 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-28774074

RESUMO

A Ge67Cu33 (16 nm) layer and a Ge (3 nm)/Ge67Cu33 (16 nm) bilayer were grown by sputtering at room temperature and used as the recording films for write-once blue laser media. In comparison to the crystallization temperature of Ge in a GeCu film (380.7 °C-405.1 °C), the crystallization temperature of Ge in a Ge/GeCu bilayer could be further decreased to 333.7 °C-382.8 °C. The activation energies of Ge crystallization were 3.51 eV ± 0.05 eV and 1.50 eV ± 0.04 eV for the GeCu and the Ge/GeCu films, respectively, indicating that the Ge/GeCu bilayer possesses a higher feasibility in high-speed optical recording applications. Moreover, the lower activation energy would lead to a larger grain size of Ge crystallization in the Ge/GeCu bilayer after the annealing process. Between the as-deposited and the annealed states, the optical contrasts (@ 405 nm) of the GeCu and the Ge/GeCu films were 26.0% and 47.5%, respectively. This reveals that the Ge/GeCu bilayer is more suitable for the recording film of a write-once blu-ray disc (BD-R) in comparison with the GeCu film. Based on the dynamic tests performed for 2× and 4× recording speeds, the optimum jitter values of the BD-R with the Ge/GeCu recording film were 7.4% at 6.3 mW and 7.6% at 8.6 mW, respectively.

9.
Opt Express ; 23(19): A1167-78, 2015 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-26406747

RESUMO

This study demonstrates the flexible white LED structure with high lumen efficiency and uniform optical performance for neutral white and warm white CCT. Flip-chip LEDs were attached on a polyimide substrate with copper strips as electrical and thermal conduction paths. Yellow phosphors are mixed with polydimenthysiloxane (PDMS) to provide mechanical support and flexibility. The light efficiency of this device can reach 120 lm/W and 85% of light output uniformity of the emission area can be achieved. Moreover, the optical simulation is employed to evaluate various designs of this flexible film in order to obtain uniform output. Both the pitch between the individual devices and the thickness of the phosphor film are calculated for optimization purpose. This flexible white LED with high lumen efficiency and good reliability is suitable for the large area fixture in the general lighting applications.

10.
Opt Express ; 23(14): 18156-65, 2015 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-26191874

RESUMO

In this study, the thin-film vertical-type AlGaInP LEDs on Cu substrates were fabricated. By performing the epitaxial lift-off (ELO) process, the LED device can be transferred from GaAs to Cu substrate. Then the GaAs substrate was separated and the ELO-LED was completed. To overcome the drawback of crack formation in the epilayer during the ELO process, various patterned Cu substrates were designed. Moreover, the finite element method was used to simulate the stress distribution in the LED sample during the ELO process. From the simulation results, an optimum structure of patterned Cu substrate was obtained since its maximum stress can be confined to the chip edges and the stress was decreased significantly during the ELO process, resulting in an apparent reduction of crack generation after separating the GaAs substrate. This optimum patterned Cu substrate was employed for the fabrication of ELO-LED. In addition, the chemical etching process was also used to etch the GaAs substrate, and this device transferred to Cu substrate was denoted as CE-LED. Based on the measurements of device performances, the forward voltages (@350 mA) of the CE-LED and ELO-LED were measured to be 2.20 and 2.29 V, while the output powers (@350 mA) of these two devices were 49.9 and 48.2 mW, respectively. Furthermore, the surface temperatures (@350 mA) of these two samples were 46.9-48.3 and 45.2-47.0 °C, respectively. Obviously, the device characteristics of the ELO-LED are very similar to those of the CE-LED. It confirms that the design of patterned Cu substrate is very helpful to obtain the thin-film vertical-type AlGaInP LEDs. Additionally, via the ELO process, the separated GaAs substrate can be reused for production cost down.

11.
ACS Appl Mater Interfaces ; 7(4): 2546-53, 2015 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-25562635

RESUMO

In this study, a spin coating process in which the grating structure comprises an Ag nanoparticle layer coated on a p-GaN top layer of InGaN/GaN light-emitting diode (LED) was developed. Various sizes of plasmonic nanoparticles embedded in a transparent conductive layer were clearly observed after the deposition of indium tin oxide (ITO). The plasmonic nanostructure enhanced the light extraction efficiency of blue LED. Output power was 1.8 times the magnitude of that of conventional LEDs operating at 350 mA, but retained nearly the same current-voltage characteristic. Unlike in previous research on surface-plasmon-enhanced LEDs, the metallic nanoparticles were consistently deposited over the surface area. However, according to microstructural observation, ITO layer mixed with Ag-based nanoparticles was distributed at a distance of approximately 150 nm from the interface of ITO/p-GaN. Device performance can be improved substantially by using the three-dimensional distribution of Ag-based nanoparticles in the transparent conductive layer, which scatters the propagating light randomly and is coupled between the localized surface plasmon and incident light internally trapped in the LED structure through total internal reflection.

12.
Opt Express ; 22 Suppl 1: A179-87, 2014 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-24921994

RESUMO

Light extraction of GaN-based light-emitting diodes grown on Si(111) substrate (GaN-on-Si based LEDs) is presented in this study. Three different designs of GaN-on-Si based LEDs with the lateral structure, lateral structure on mirror/Si(100) substrate, and vertical structure on mirror/Si(100) substrate were epitaxially grown by metalorganic chemical vapor deposition and fabricated using chemical lift-off and double-transfer techniques. Current-voltage, light output power, far-field radiation patterns, and electroluminescence characteristics of these three LEDs were discussed. At an injection current of 700 mA, the output powers of LEDs with the lateral structure on mirror/Si(100) substrate and vertical structure on mirror/Si(100) substrate were measured to be 155.07 and 261.07 mW, respectively. The output powers of these two LEDs had 70.63% and 187.26% enhancement compared to that of LED with the lateral structure, respectively. The result indicated this vertical structure LED was useful in improving the light extraction due to an enhancement in light scattering efficiency while the high-reflection mirror and diffuse surfaces were employed.

13.
Opt Express ; 21(21): 24599-610, 2013 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-24150304

RESUMO

This study evaluates the effect of crystallinity and point defects on time-dependent photoresponsivity and the cathodoluminescence (CL) properties of ß-Ga2O3 epilayers. A synchrotron high-resolution X-ray technique was used to understand the crystalline structure of samples. Rutherford backscattering spectroscopy was used to determine the net chemical composition of the samples to examine the type and ratio of their possible point defects. The results show that in functional time-dependent photoresponsivity of photodetectors based on ß-Ga2O3 epilayers, point defects contribution overcomes the contribution of crystallinity. However, the crystalline structure affects the intensities and emission regions of CL spectra more than point defects.

14.
Opt Express ; 21(6): 7337-42, 2013 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-23546117

RESUMO

InGaN films with 33% and 60% indium contents were deposited by pulsed laser deposition (PLD) at a low growth temperature of 300 °C. The films were then annealed at 500-800 °C in the non-vacuum furnace for 15 min with an addition of N(2) atmosphere. X-ray diffraction results indicate that the indium contents in these two films were raised to 41% and 63%, respectively, after annealing in furnace. In(2)O(3) phase was formed on InGaN surface during the annealing process, which can be clearly observed by the measurements of auger electron spectroscopy, transmission electron microscopy and x-ray photoelectron spectroscopy. Due to the obstruction of indium out-diffusion by forming In(2)O(3) on surface, it leads to the efficient increment in indium content of InGaN layer. In addition, the surface roughness was greatly improved by removing In(2)O(3) with the etching treatment in HCl solution. Micro-photoluminescence measurement was performed to analyze the emission property of InGaN layer. For the as-grown InGaN with 33% indium content, the emission wavelength was gradually shifted from 552 to 618 nm with increasing the annealing temperature to 800 °C. It reveals the InGaN films have high potential in optoelectronic applications.


Assuntos
Gálio/química , Gálio/efeitos da radiação , Índio/química , Índio/efeitos da radiação , Lasers , Membranas Artificiais , Dureza , Temperatura Alta , Propriedades de Superfície/efeitos da radiação , Vácuo
15.
Opt Express ; 20 Suppl 5: A597-605, 2012 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-23037527

RESUMO

In this study, cup-shaped copper sheets were developed to improve heat dispassion for high-power light emitting diodes (LEDs) array module (3 × 3, 4 × 4, and 5 × 5) using an electroplating technique. The cup-shaped copper sheets were directly contacted with sapphire to enhance the heat dissipation of the chip itself. The lateral emitting light extraction and heat dissipation of high-power LEDs were enhanced and efficient. The surface temperature was not only decreasing but also uniform for each LED chip with the cup-shaped copper heat spreader adoption. The high thermal transmitting performance of cup-shaped copper heat spreader allows thermal resistance reducing 0.7, 0.6, and 0.7 K/W of 3 × 3, 4 × 4, and 5 × 5 LED array module, respectively. In addition, the light output power was increased of 14, 13, and 12% with 3 × 3, 4 × 4, and 5 × 5 LEDs array module using cup-shaped copper sheet at high current injection. High heat dissipation performance and light extraction were obtained by cup-shaped copper sheet with copper bulk and silver mirror.

16.
J Nanosci Nanotechnol ; 12(2): 1440-3, 2012 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-22629974

RESUMO

The single-layered Fe-Pt films with thickness of 30 nm are in-situ deposited directly on Si substrate at various substrate temperatures (Ts) of 350 to 590 degrees C. As the Fe-Pt film is sputtered at substrate temperature is 350 degrees C, it shows (111) preferred orientation and tends to in-plane magnetic anisotropy. The L1(0) Fe-Pt film with (001) texture is obtained and exhibited perpendicular magnetic anisotropy as the substrate temperature is increased to 470 degrees C. The perpendicular coercivity (Hc perpendicular), saturation magnetization (Ms) and perpendicular squareness (S perpendicular) of this film are 6.9 kOe, 674 emu/cm3 and 0.89, respectively, which reveal its significant potential as perpendicular magnetic recording media.

17.
Opt Express ; 19(17): 16244-51, 2011 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-21934987

RESUMO

In this study, indium-tin oxide (ITO)/Al-doped zinc oxide (AZO) composite films were fabricated by pulsed laser deposition and used as transparent contact layers (TCLs) in GaN-based blue light emitting diodes (LEDs). The ITO/AZO TCLs were composed of the thin ITO (50 nm) films and AZO films with various thicknesses from 200 to 1000 nm. Conventional LED with ITO (200 nm) TCL prepared by E-beam evaporation was fabricated and characterized for comparison. From the transmittance spectra, the ITO/AZO films exhibited high transparency above 90% at wavelength of 465 nm. The sheet resistance of ITO/AZO TCL decreased as the AZO thickness increased, which could be attributed to the increase in a carrier concentration, leading to a decrease in the forward bias of LED. The LEDs with ITO/AZO composite TCLs showed better light extraction as compared to LED with ITO TCL in compliance with simulation. When an injection current of 20 mA was applied, the output power for LEDs fabricated with ITO/AZO TCLs had 45%, 63%, and 71% enhancement as compared with those fabricated using ITO (200 nm) TCL for the AZO thicknesses of 200, 460, and 1000 nm, respectively.

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