Jyh-Rong Gong

Performance of InGaN/GaN MQW LEDs Using Ga-Doped ZnO TCLs Prepared by ALD

Heavily Ga-doped ZnO (n±-GZO) films prepared by atomic layer deposition were used as transparent conducting layers (TCLs) on InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs). It was found that N₂-annealed n⁺-GZO-coated InGaN/GaN MQW LEDs exhibited reduced forward voltage and enhanced light extraction under certain conditions. A forward voltage of 3.1 V at 20 mA was achieved for a 400°C N₂-annealed n⁺-GZO-coated InGaN/GaN MQW LED with a specific contact resistance of the n⁺-GZO on p-GaN contact being 4.1 × 10^-3 Ω cm². Compared to the same InGaN/GaN MQW LED structure with a commercial grade indium tin oxide (ITO) TCL, the 400 °C N₂-annealed n⁺-GZO-coated InGaN/GaN MQW LED shows an increment of light output power by 15% at 20 mA. It is believed that the enhanced light extraction of the n⁺-GZO-coated InGaN/GaN MQW LED is a consequence of a higher refractive index of n⁺-GZO than that of ITO.

Observation of compositional pulling phenomenon in AlxGa1-xN (0.4<x<1.0) films grown on (0001) sapphire substrates

High Al content AlxGa1−xN (0.4<x<1.0) films were grown at 1050 °C either on (0001) sapphire substrates or on AlN films by alternative supply of group III metalorganics (trimethylaluminum and trimethylgallium) and NH3 in an inductively heated quartz reactor operated at atmospheric pressure. θ–2θ x-ray diffraction data show a compositional separation in the AlxGa1−xN films grown on low-temperature (LT) aluminum nitride (AlN) buffer layer-coated (0001) sapphire substrates. Absorption spectroscopic measurements also reveal double cutoff edges in the AlxGa1−xN sample grown directly on a LT AlN-coated (0001) sapphire substrate while only one absorption edge having higher energy was observed in the AlxGa1−xN film grown on a 0.1-μm-thick high-temperature (HT) AlN intermediate layer, which was deposited on top of the (0001) sapphire substrate. Cross-sectional transmission electron microscopic observations show the bilayer nature of the AlxGa1−xN films grown directly on the LT AlN-coated sapphire substrate. Such a ...

Growth and characterization of GaN films on (0001) sapphire substrates by alternate supply of trimethylgallium and NH3

Abstract GaN films were grown on (0001) sapphire substrates in a temperature range of 500∼950°C by exposing the substrates to trimethylgallium (TMG) and NH 3 one at a time. High quality GaN films were achieved at 800∼900°C with a thin GaN buffer layer predeposited at 500°C. The linewidth of the (0004) double-crystal rocking curve X-ray diffraction (DCXRD) of a 2.0 μm thick GaN film is about 250∼500 arcsec. Increment in growth temperature over a temperature range of 800∼900°C is helpful to suppress the intensity of yellow luminescence and to enhance the luminescence intensity of the near band-to-band emission. Typically, the room temperature photoluminescence intensity ratio of the near band edge emission to the yellow luminescence for an as-grown high quality GaN film is more than one order of magnitude. The best GaN films with superior optical behavior were achieved at ∼900°C with a V/III ratio of 5000. Photoluminescence measurements of these GaN films at 9 K show strong and sharp near band-to-band emission with almost no yellow luminescence.

Effects of Al-containing Intermediate III-nitride Strained Multilayers on the Threading Dislocation Density and Optical Properties of GaN Films

We report the influence of intermediate AlN/GaN, AlGaN/GaN or AlN/AlGaN strained multilayer structures on the threading dislocation (TD) density and optical properties of GaN films. A series of GaN films were deposited at 1050°C on (0001) sapphire substrates using intermediate AlN/GaN, AlGaN/GaN or AlN/AlGaN strained multilayer structures. Etching pit density (EPD) counts and transmission electron microscopic (TEM) studies show that the implementation of AlN/GaN and AlGaN/GaN in GaN films enables the blocking of TDs in the films very efficiently. Photoluminescence (PL) measurements exhibit the increment of near band edge emission intensity in the GaN films having Al0.5Ga0.5N/GaN or AlN/GaN intermediate strained multilayer structures. Cross-sectional TEM observations show that TD annihilation and de-multiplication processes play important roles in the TD density reduction in the GaN films having Al-containing strained multilayer structures.

Electro-colorimetric hydrogen gas sensor based on Pt-functionalized In 2 O 3 nanopushpins and InGaN/GaN multiple quantum wells

A novel electro-colorimetric gas sensing technique based on the catalytic metal nanoparticles decorated metal oxide nanostructures integrated with multiple quantum wells (MQWs) has been proposed. The working principle has been demonstrated by the sensing device derived from the composite consisting of In0.15Ga0.85N/GaN MQWs and Pt-functionalized In2O3 nanopushpins for the detection of hydrogen gas. The pronounced changes in emission as well as Raman scattering spectra of InGaN/GaN MQWs under different target gas concentrations clearly illustrate the feasibility of our newly designed composites for the derivative of contact-free, simple and highly sensitive gas sensors with optical detection

Characteristics and interactions of threading dislocations in GaN films grown on (0001) sapphire substrates with or without short-period superlattice insertion

In this study, transmission electron microscopy was employed to investigate the characteristics of threading dislocations (TDs) in GaN films grown on the (0001) sapphire substrates with or without the insertion of Al0.3Ga0.7N (2 nm)/GaN (2 nm) short period superlattices (SPSLs). By using gb = 0 invisibility criterion, it was found that most of the TDs were type a TDs in a GaN film either containing SPSL or having no SPSL insertion. Type a + c TDs were found to nucleate through the interactions between type a and type c TDs in GaN near the GaN/sapphire interface. Some of the type a TDs were observed to bend along GaN basal plane because of the influence of biaxial strain near the GaN/SPSL interface.

On the physical properties of In2O3 films grown on (0001) sapphire substrates by atomic layer deposition

The properties of In2O3 films grown on (0001) plane sapphire substrates by atomic layer deposition using trimethylindium and nitrous oxide were investigated. Using x-ray diffraction and scanning and transmission electron microscopies, In2O3 films were found to deposit on sapphire substrates with their (222) planes parallel to the (0001) planes of sapphire. It was found that there were twin structures inside the In2O3 film with twin boundaries along the {112¯} planes. Most In2O3 films deposited on thermally annealed low-temperature-In2O3 buffer-layer-coated substrates exhibited high optical transmittance, low electron concentration, and high electron mobility. The best In2O3 film achieved shows an average transmittance of ∼90% in the visible regime with electron concentration and mobility being ∼2×1016 cm−3 and ∼60 cm2/V s, respectively, at room temperature.

Comparison of the performance of InGaN/AlGaN MQW LEDs grown on c-plane and a-plane sapphire substrates

We report a comparative study on the performance of InGaN/AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) fabricated on c- and a-plane sapphire substrates, respectively. It was found that the LEDs grown on a-plane sapphire substrates exhibited enhanced electroluminescence intensity, decreased double crystal X-ray diffraction linewidth, reduced etching pit density, and smaller ideality factor compared to those deposited on c-plane sapphire substrates. The improved LED characteristics are attributed to threading dislocation density decrement inside the LEDs due to the reduced mismatch between LED structure and a-plane sapphire substrate.

Cu3Ge Schottky contacts on n-GaN

AbstractThe electrical properties and thermal stability of