Search results

The purpose of this paper is to investigate the effect of growth temperature on the evolution of indium incorporation and the growth process of InGaN/GaN heterostructures.

To examine this effect, the InGaN/GaN heterostructures were grown using Taiyo Nippon Sanso Corporation metal-organic chemical vapor deposition (MOCVD) SR4000-HT system. The InGaN/GaN heterostructures were epitaxially grown on 3.4 µm undoped-GaN (ud-GaN) and GaN nucleation layer, respectively, over a commercial 2” c-plane flat sapphire substrate. The InGaN layers were grown at different temperature settings ranging from 860°C to 820°C in a step of 20°C. The details of structural, surface morphology and optical properties were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), atomic force microscopy and ultraviolet-visible (UV-Vis) spectrophotometer, respectively.

InGaN/GaN heterostructure with indium composition up to 10.9% has been successfully grown using the MOCVD technique without any phase separation detected within the sensitivity of the instrument. Indium compositions were estimated through simulation fitting of the XRD curve and calculation of Vegard’s law from UV-Vis measurement. The thickness of the structures was determined using the Swanepoel method and the FE-SEM cross-section image.

This paper report on the effect of MOCVD growth temperature on the growth process of InGaN/GaN heterostructure, which is of interest in solid-state lighting technology, especially in light-emitting diodes and solar cell application.

This study aims to investigate the effects of indium composition on surface morphology and optical properties of indium gallium nitride on gallium nitride (InGaN/GaN) heterostructures.

The InGaN/GaN heterostructures were grown on flat sapphire substrates using a metal-organic chemical vapour deposition reactor with a trimethylindium flow rate of 368  sccm. The indium composition of the InGaN epilayers was controlled by applying different substrate temperatures. The surface morphology and topography were observed using field emission scanning electron microscope (F.E.I. Nova NanoSEM 450) and atomic force microscopy (Bruker Dimension Edge) with a scanning area of 10 µm × 10 µm, respectively. The compositional analysis was done by Energy Dispersive X-Ray Analysis. Finally, the ultraviolet-visible (UV-Vis) spectrophotometer (Agilent Technology Cary Series UV-Vis-near-infrared spectrometer) was measured from 200 nm to 1500 nm to investigate the optical properties of the samples.

The InGaN/GaN thin films have been successfully grown at three different substrate temperatures. The indium composition reduced as the temperature increased. At 760 C, the highest indium composition was obtained, 21.17%. This result was acquired from the simulation fitting of ω−2θ scan on (0002) plane using LEPTOS software by Bruker D8 Discover. The InGaN/GaN shows significantly different surface morphologies and topographies as the indium composition increases. The thickness of InGaN epilayers of the structure was ∼300 nm estimated from the field emission scanning electron microscopy. The energy bandgap of the InGaN was 2.54 eV – 2.79 eV measured by UV-Vis measurements.

It can be seen from this work that changes in substrate temperature can affect the indium composition. From all the results obtained, this work can be helpful towards efficiency improvement in solar cell applications.

The aims of this paper is to study the effects of the V/III ratio of indium gallium nitride (InGaN) quantum wells (QWs) on the structural, optical and electrical properties of near-ultraviolet light-emitting diode (NUV-LED).

InGaN-based NUV-LED is successfully grown on the c-plane patterned sapphire substrate at atmospheric pressure using metal organic chemical vapor deposition.

The indium composition and thickness of InGaN QWs increased as the V/III ratio increased from 20871 to 11824, according to high-resolution X-ray diffraction. The V/III ratio was also found to have an important effect on the surface morphology of the InGaN QWs and thus the surface morphology of the subsequent layers. Apart from that, the electroluminescence measurement revealed that the V/III ratio had a major impact on the light output power (LOP) and the emission peak wavelength of the NUV-LED. The LOP increased by up to 53% at 100 mA, and the emission peak wavelength of the NUV-LED changed to a longer wavelength as the V/III ratio decreased from 20871 to 11824.

This study discovered a relation between the V/III ratio and the properties of QWs, which resulted in the LOP enhancement of the NUV-LED. High TMIn flow rates, which produced a low V/III ratio, contribute to the increased LOP of NUV-LED.

This paper aims to report on the use of radio frequency nitrogen plasma‐assisted molecular beam epitaxy (RF‐MBE) to grow high‐quality n‐type In_0.47Ga0.53N/GaN on Si(111) substrate using AlN as a buffer layer.

Structural analyses of the InGaN films were performed by using X‐ray diffraction, atomic force microscopy, and Hall measurement. Metal‐semiconductor‐metal (MSM) photodiode was fabricated on the In_0.47Ga0.53N/Si(111) films. Electrical analysis of the MSM photodiodes was carried out by using current‐voltage (I‐V) measurements. Ideality factors and Schottky barrier heights for Ni/In_0.47Ga0.53N, was deduced to be 1.01 and 0.60 eV, respectively.

The In_0.47Ga0.53N MSM photodiode shows a sharp cut‐off wavelength at 840 nm. A maximum responsivity of 0.28 A/W was achieved at 839 nm. The detector shows a little decrease in responsivity from 840 to 200 nm. The responsivity of the MSM drops by nearly two orders of magnitude across the cut‐off wavelength.

Focuses on III‐nitride semiconductors, which are of interest for applications in high temperature/power electronic devices.

The purpose of this paper is to enhance the efficiency of the LED by introducing three-step magnesium (Mg) doping profile. Attention was paid to the effects of the Mg doping concentration of the first p-GaN layer (i.e. layer close to the active region). Attention was paid to the effects of the Mg doping concentration of the first p-GaN layer (i.e. layer close to the active region).

Indium gallium nitride (InGaN)–based light-emitting diode (LED) was grown on a 4-inch c-plane patterned sapphire substrate using metal organic chemical vapor deposition. The Cp₂Mg flow rates for the second and third p-GaN layers were set at 50 sccm and 325 sccm, respectively. For the first p-GaN layer, the Cp₂Mg flow rate varied from 150 sccm to 300 sccm to achieve different Mg dopant concentrations.

The full width at half maximum (FWHM) for the GaN (102) plane increases with increasing Cp₂Mg flow rate. FWHM for the sample with 150, 250 and 300 sccm Cp₂Mg flow rates was 233 arcsec, 236 arcsec and 245 arcsec, respectively. This result indicates that the edge and mixed dislocations in the p-GaN layer were increased with increasing Cp₂Mg flow rate. Atomic force microscopy (AFM) results reveal that the sample grown with 300 sccm exhibits the highest surface roughness, followed by 150 sccm and 250 sccm. The surface roughness of these samples is 2.40 nm, 2.12 nm and 2.08 nm, respectively. Simultaneously, the photoluminescence (PL) spectrum of the 250 sccm sample shows the highest band edge intensity over the yellow band ratio compared to that of other samples. The light output power measurements found that the sample with 250 sccm exhibits high output power because of sufficient hole injection toward the active region.

Through this study, the three steps of the Mg profile on the p-GaN layer were proposed to show high-efficiency InGaN-based LED. The optimal Mg concentration was studied on the first p-GaN layer (i.e. layer close to active region) to improve the LED performance by varying the Cp₂Mg flow rate. This finding was in line with the result of PL and AFM results when the samples with 250 sccm have the highest Mg acceptor and good surface quality of the p-GaN layer. It can be deduced that the first p-GaN layer doping has a significant effect on the crystalline quality, surface roughness and light emission properties of the LED epi structure.

To design and optimize the traditional aluminum gallium nitride/gallium nitride high electron mobility transistor (HEMT) device in achieving improved performance and current handling capability using the Synopsys’ Sentaurus TCAD tool.

Varying material and physical considerations, specifically investigating the effects of graded barriers, spacer interlayer, material selection for the channel, as well as study of the effects in the physical dimensions of the HEMT, have been extensively carried out.

Critical figure-of-merits, specifically the DC characteristics, 2DEG concentrations and mobility of the heterostructure device, have been evaluated. Significant observations include enhancement of maximum current density by 63 per cent, whereas the electron concentration was found to propagate by 1,020 cm⁻³ in the channel.

This work aims to provide tactical optimization to traditional heterostructure field effect transistors, rendering its application as power amplifiers, Monolithic Microwave Integrated Circuit (MMICs) and Radar, which requires low noise performance and very high radio frequency design operations.

Analysis in covering the breadth and complexity of heterostructure devices has been carefully executed through extensive TCAD modeling, and the end structure obtained has been optimized to provide best performance.

The purpose of this study is to identify and explore what leadership characteristics constitute humanistic leadership in the South Korean context. Moreover, this study examines how these leadership characteristics are connected to Korean culture.

Based on the information gathered from semi-structured interviews and other sources, including books, case study articles and news articles, this study captures a more comprehensive perspective of Mr. Kook-Hyun Moon, the former CEO of Yuhan–Kimberly.

The key characteristics of Mr. Moon's humanistic leadership that are identified in this study are: respect for all mankind, benevolence (seeking the greater good), sincerity (building trusting relationships with stakeholders) and continuous learning and innovation (developing self and others). These key characteristics set Mr. Moon apart from other leaders and are connected to the fundamental values and philosophies of Korean culture.

This study contributes to the current leadership literature by identifying and exploring Mr. Moon's humanistic leadership characteristics that enable him to gain respect and contribute to communities and society in the South Korean context. This study also finds that the humanistic leadership characteristics of Mr. Moon reflect three major attributes of Korean culture: the ideology of the Dangun mythology, the principle of Neo-Confucianism in Korea and jeong – an indigenous cultural concept in Korea (these attributes will be discussed in detail in the South Korean values and philosophies section). Such reflection suggests that investigating how humanistic leadership characteristics are connected to local cultural roots is important to enhance the understanding of humanistic leadership.

This study aims to focus on roughening N-face (backside) GaN substrate prior to GaN-on-GaN light-emitting diode (LED) growth as an attempt to improve the LED performance.

The N-face of GaN substrate was roughened by three different etchants; ammonium hydroxide (NH4OH), a mixture of NH₄OH and H₂O₂ (NH₄OH: H₂O₂) and potassium hydroxide (KOH). Hexagonal pyramids were successfully formed on the surface when the substrate was subjected to the etching in all cases.

Under 30 min of etching, the highest density of pyramids was obtained by NH4OH: H₂O₂ etching, which was 5 × 10⁹ cm^–2. The density by KOH and NH₄OH etchings was 3.6 × 10⁹ and 5 × 10⁸ cm^–2, respectively. At standard operation of current density at 20 A/cm², the optical power and external quantum efficiency of the LED on the roughened GaN substrate by NH₄OH: H₂O₂ were 12.3 mW and 22%, respectively, which are higher than its counterparts.

This study demonstrated NH₄OH: H₂O₂ is a new etchant for roughening the N-face GaN substrate. The results showed that such etchant increased the density of the pyramids on the N-face GaN substrate, which subsequently resulted in higher optical power and external quantum efficiency to the LED as compared to KOH and NH₄OH.

The purpose of this paper is to study the structural and optical characterization of Al_x In_y Ga_1−x−y N quaternary epilayers, which were grown on c‐plane (0001) sapphire substrates with AlN as buffer layers using plasma assisted molecular beam epitaxy technique with indium (In) mole fraction y ranging from 0.0 to 0.1 and constant aluminum (Al) mole fraction x=0.06.

High‐resolution X‐ray diffraction rocking curve (HRXRD‐RC), scanning electron microscopy (SEM), energy dispersive X‐ray spectrometry (EDX), and photoluminescence (PL) spectroscopy have been measured on quaternary Al_x In_y Ga_1−x−y N thin films at room temperature.

HRXRD‐RC measurements confirmed that the Al_x In_y Ga_1−x−y N alloys had wurtzite structure. SEM images, element composition analysis by EDX, provided the evidence to show the existence of defects inside the samples contaminated by silicon from previous growth leading to nonuniformity of the epilayers, which caused decreased in the quality of the samples. PL spectra show reducing of the integrated intensity and an increasing red shift with increasing in content with reference to the ternary sample Al_0.06Ga_0.94N. The existence of a large amount of nonradiative recombination centers are responsible for the reduced the luminescence and the red shift provided evidence to an increase in composition inside the Al_x In_y Ga_1−x−y N quaternary alloys. Photoluminescence is used to determine the behavior of the near band edge emission represent the energy band gap of the quaternary films. The energy band gap decreases with increasing In composition from 0.01 to 0.1 mole fraction. This trend is expected since the incorporation of in reduced the energy band gap of ternary Al_0.06Ga_0.94N (3.529 eV). We have also investigated the bowing parameter of the variation of energy band gaps and found it to be very sensitive on in composition. A value of b=10.95 have been obtain for our quaternary Al_x In_y Ga_1−x−y N alloys.

This study on quaternary samples described in this paper, clearly indicates that the present of defects due to impurity contaminations has a dominant role in determining the structural and optical properties of Al_x In_y Ga_1−x−y N quaternary alloys.

Porous silicon (Si) was fabricated by using three different wet etching methods, namely, direct current photo-assisted electrochemical (DCPEC), alternating CPEC (ACPEC) and two-step ACPEC etching. This study aims to investigate the structural properties of porous structures formed by using these etching methods and to identify which etching method works best.

Si n(100) was used to fabricate porous Si using three different etching methods (DCPEC, ACPEC and two-step ACPEC). All the samples were etched with the same current density and etching duration. The samples were etched by using hydrofluoric acid-based electrolytes under the illumination of an incandescent lamp.

Field emission scanning electron microscopy (FESEM) images showed that porous Si etched using the two-step ACPEC method has a higher porosity and density than porous Si etched using DCPEC and ACPEC. The atomic force microscopy results supported the FESEM results showing that porous Si etched using the two-step ACPEC method has the highest surface roughness relative to the samples produced using the other two methods. High resolution X-ray diffraction revealed that porous Si produced through two-step ACPEC has the highest peak intensity out of the three porous Si samples suggesting an improvement in pore uniformity with a better crystalline quality.

Two-step ACPEC method is a fairly new etching method and many of its fundamental properties are yet to be established. This work presents a comparison of the effect of these three different etching methods on the structural properties of Si. The results obtained indicated that the two-step ACPEC method produced an etched sample with a higher porosity, pore density, surface roughness, improvement in uniformity of pores and better crystalline quality than the other etching methods.