Hunsoo Jeon

Characterization of the InGaN/GaN Multi-Quantum-Wells Light-Emitting Diode Grown on Patterned Sapphire Substrate with Wide Electroluminescence Spectrum

We report the characterization of the InGaN/GaN multi-quantum-well (MQW) light-emitting diode (LED) grown on a patterned sapphire substrate by metal organic chemical vapor deposition (MOCVD) using the selective area growth (SAG) method. The SAG patterns were designed to be circular and their diameters were 700 and 200 µm. After the growth, the InGaN/GaN MQW LED of 200 µm diameter had various crystal facets and a shape similar to volcanic craters, which were not observed in the 700-µm-diameter sample. We obtained an active layer with compositional nonuniformity and superior optical properties. We found wide electroluminescence (EL) spectral peaks near 470, 570, and 600 nm. The distribution of the EL spectrum of the sample was similar to that of a conventional phosphor-converted white LED.

Mechanism of light emission and manufacturing process of vertical-type light-emitting diode grown by hydride vapor phase epitaxy

We developed a vertical-type light-emitting diode (LED) in which the substrate is removed using a hydride vapor phase epitaxy (HVPE) apparatus consisting of a multi-graphite boat filled with a mixed source and a high-temperature (T ≈ 900 °C) RF heating coil outside the source zone. The new chip-growth process with a significant reduction in the number of production steps is completed in only four steps, namely, photolithography, epitaxial layer growth, sorting, and metallization. We analyze the emission mechanism of these lights from measurement results to validate the characteristics of the light emitted from these vertical-type blue LEDs and white LEDs (WLEDs) without substrates, and propose that this mixed-source HVPE method may be a promising production technique for LEDs.

Growth of AlN layer on patterned sapphire substrate by hydride vapor phase epitaxy

Even though a patterned sapphire substrate (PSS) has been used for the growth of a high-quality epilayer because of its many advantages, it has not been successfully used to grow an AlN epilayer for ultraviolet (UV) light-emitting diodes (LEDs) on a PSS up to now. We report the growth of a high-quality AlN epilayer on a PSS, as a substrate for the manufacture of UV LEDs, by hydride vapor phase epitaxy (HVPE). The X-ray diffraction (XRD) peaks for the AlN epilayer grown on the PSS indicate that crystalline AlN with a wurtzite structure was grown successfully on the PSS. Furthermore, HVPE combining both in situ HVPE technology and liquid-phase epitaxy (LPE) using a mixed source is proposed as a novel method for the growth of a flat AlN epilayer on a PSS.

The properties of AlGaN epi layer grown by HVPE

The AlGaN layer has direct wide bandgaps ranging from 3.4 to 6.2 eV. Nowadays, it is becoming more important to fabricate optical devices in an UV region for the many applications. The high quality AlGaN layer is necessary to establish the UV optical devices. However, the growth of AlGaN layer on GaN layer is difficult due to the lattice mismatch and difference thermal expansion coefficient between GaN layer and AlGaN layer. In this paper, we attempted to grow the LED structure on GaN template by mixed-source HVPE method with multi-sliding boat system. We tried to find the optical and lattice transition of active layer by control the Al content in mixed-source. For the growth of epi layer, the HCl and gas were flowed over the mixed-source and the carrier gas was . The temperature of source zone and growth zone was stabled at 900 and , respectively. After the growth, we performed the x-ray diffraction (XRD) and electro luminescence (EL) measurement.

Crystal Orientation of GaN Nanostructures Grown on Al2O3 and Si(111) with a Zr Buffer Layer

We studied the crystallographic orientation of GaN nanostructures grown on Si(111) and Al2O3 substrates. We evaluated Zr metal as a novel alternative to conventional buffer layers such as AlN and ZnO. One-dimensional structures (nanorods and nanoneedles) were grown by hydride vapor phase epitaxy at 650 and 600 °C, and investigated using field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis. FE-SEM images showed that the GaN nanorods had a uniform diameter along the growth direction. XRD results indicated that the nanostructures had a hexagonal crystal structure, and pole figure measurements revealed that GaN nanostructures grown on the Si(111) substrate had a stronger c-axis crystallographic orientation than those grown on the Al2O3 substrate.

AlN and AlGaN layers grown on Si(111) substrate by mixed-source hydride vapor phase epitaxy method

High Al-composition AlGaN and AlN epilayers were grown directly on Si(111) substrate by a hydride vapor phase epitaxy (HVPE) method with a melted mixed source in a graphite boat set in a source zone with high temperatures of T = 700 and 800 °C, respectively. The presence of the Ga material in the mixed source of Ga and Al promoted the growth of AlN and AlGaN epilayers in the growth zone. When the temperature in the source zone was 800 °C, the crystalline quality of the AlN and AlGaN epilayers increased as the ratio of Ga to Al increased, and the optimum mix ratio of Ga to Al for the growth of AlN epilayers was approximately 0.35–0.42, obtained from a numerical fitting analysis of the X-ray diffraction (XRD) data for these epilayers. It appears that they can be grown directly by our melted-mixed-source HVPE method in a high-temperature source zone.

Nonphosphor White Light Emitting Diodes by Mixed-Source Hydride Vapor Phase Epitaxy

In this paper, we approached a novel fabrication for non phosphor white light emitting diodes (LEDs) by the growth of AlGaN/InAlGaN double-hetero structures using by mixed-source hydride vapor phase epitaxy (HVPE) system with multi-sliding boat. It is unique crystal growth technology different from conventional HVPE and metal organic chemical vapor deposition (MOCVD) system using mixed metal source of aluminum, indium and gallium. The characterization of non phosphor white LEDs was examined by photoluminescence (PL) and electroluminescence (EL). The results of EL were found green and yellow emissions as spectrum peaks near 500, 550, and 610 nm definitely. The CIE chromaticity coordinates of white LEDs was measured at injection current 30 mA. Our results are nearly positions; at x = 0.28 and y = 0.31. Even though the LED needs more improved in optical properties, we demonstrated achieving phosphor-free solid-state white lighting.

Fabrication of the CuInGaSe Pellet and Characterization of the Thin Film

CuInGaSe (CIGS) mixed-source was prepared by hydride vapor transport method (HVT). The new source synthesis method was attempted by mixing several metals such as Cu, In, Ga, and Se with 3:5:1:4 mass ratios. This mixed-source was soaked at 1090 °C for 90 min in nitrogen atmosphere. Then, the CIGS was grinded up and formed the state of powder and the CIGS pellet was made by pressure machine. The diameter of pellet is 10 mm. The CIGS thin film was deposited on soda lime glass with evaporated molybdenum layer by e-beam evaporating this CIGS pellet. For crystallization of CIGS thin film, we measured scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). High intensity X-ray peaks diffracted from (112), (204)/(220), (116)/(312), and (400) of CIGS thin film and from (110) of Mo were confirmed by XRD measurement.

Fabrication of selective-area growth InGaN LED by mixed-source hydride vapor-phase epitaxy

We prepared InGaN light-emitting diodes (LEDs) with the active layers grown from a mixed source of Ga–In–N materials on an n-type GaN substrate by a selective-area growth method and three fabrication steps: photolithography, epitaxial layer growth, and metallization. The preparation followed a previously developed experimental process using apparatus for mixed-source hydride vapor-phase epitaxy (HVPE), which consisted of a multi-graphite boat, for insulating against the high temperature and to control the growth rate of epilayers, filled with the mixed source on the inside and a radio-frequency (RF) heating coil for heating to a high temperature (T > 900 °C) and for easy control of temperature outside the source zone. Two types of LEDs were prepared, with In compositions of 11.0 and 6.0% in the InGaN active layer, and room-temperature electroluminescence measurements exhibited a main peak corresponding to the In composition at either 420 or 390 nm. The consecutive growth of InGaN LEDs by the mixed-source HVPE method provides a technique for the production of LEDs with a wide range of In compositions in the active layer.

Characterization of carbon microspheres grown by HVPE

The carbon microspheres of a core-shell type were grown by the method of mixed-source hydride vapor phase epitaxy (HVPE). The surface and the cross section of the carbon microsphere grown by a new method were observed by scanning electron microscope (SEM). The characteristics of the carbon microsphere were investigated by X-ray photoelectron spectroscopy (XPS) and a high resolution-transmission electron microscope (HR-TEM). From these measurements, the diameters of carbon sphere were about few hundred micrometers. Furthermore, we show that the carbon microsphere of the core-shell type by mixed-source HVPE method can be grown successfully with the larger size than those of the existing one. This mixed-source HVPE method is proposed a new method for making of carbon microsphere.