Se Yeon Jung

Formation of low-resistance Ohmic contacts to N-face n-GaN for high-power GaN-based vertical light-emitting diodes

We report on the formation of low-resistance Ohmic contacts to N-face n-GaN for high-power vertical light-emitting diodes using an Al–Ga solid solution (50 nm)/Ti(30 nm)/Al(200 nm) scheme and compare them with Ti(30 nm)/Al(200 nm) contacts. The Al–Ga solid solution layer is introduced to minimize the formation of Ga vacancies near the N-face n-GaN surface. It is shown that, unlike the Ti/Al contacts, the Al–Ga solid solution/Ti/Al contacts exhibit Ohmic behavior with a resistivity of 4.1×10−4 Ω cm2, even after annealing at 250 °C. X-ray photoemission spectroscopy and secondary ion mass spectrometry examinations are performed to understand the temperature dependence of the electrical properties.

Electrical Characteristics of V/Ti/Au Contacts to Ga-Polar and N-Polar n-GaN Prepared by Different Methods

We have investigated the electrical properties of V (20 nm)/Ti (60 nm)/Au (20 nm) contacts to Ga- and N-polar n-GaN. Regardless of the crystal polarities, all the samples exhibit similar electrical characteristics. The as-deposited samples are ohmic. However, they become nonohmic when annealed at 300-500°C. The samples are ohmic again at 700°C. Based on the X-ray photoemission spectroscopy and Auger electron spectroscopy results, the ohmic and degradation behaviors are explained in terms of the formation of donorlike surface defects and Ga vacancies, which are generated by dry etching, the out-diffusion of Ga, and the formation of nitride phases.

Improved Light Output Power of GaN-Based Light Emitting Diodes by Enhancing Current Spreading Using Single-Wall Carbon Nanotubes

Single-wall carbon nanotubes (SWCNTs) have been combined with indium tin oxide (ITO) to improve the output power of GaN-based light emitting diodes (LEDs). LEDs fabricated with the SWCNT/ITO contacts give a forward voltage of 3.61 V at 350 mA, which is slightly higher than that of LEDs with ITO-only contacts. The SWCNT/ITO and ITO-only contacts produce transmittance values of 91.5 and 94.4% at 460 nm, respectively. However, LEDs with SWCNTs show a higher output power by 60% at 20 mA compared to those without SWCNTs. Photoemission microscope analyses show that the well-dispersed SWCNT bundle efficiently serves as a current spreader.

Electrical properties of Ti/Al ohmic contacts to sulfur-passivated N-Face n-type GaN for vertical-structure light-emitting diodes

We investigate the electrical properties of Ti/Al ohmic contacts on (NH 4 ) 2 S x -passivated N-face n-GaN:Si (4.2 X 10 18 cm ―3 ) grown by molecular beam epitaxy. It is shown that the passivation results in an increase in the photoluminescence intensity of n-GaN. Current―voltage (I-V) measurements show that the passivated samples experience a slight degradation in the electrical properties upon annealing at 300°C, while the untreated samples show some improvement although still nonohmic. Based on the I-V and X-ray photoemission spectroscopy results, we describe the possible mechanisms for the passivation and annealing dependence of the electrical properties of the Ti/Al contacts to the N-face n-GaN.

Di-block copolymer directed anodization of hexagonally ordered nanoporous aluminum oxide

Porous anodized aluminum oxide (AAO) nanostructures have been extensively investigated as versatile templates for nanodots and nanowires for many applications. Such self-ordered AAO structures are often achieved by so-called two-step anodization. Ordered pore arrangements can be obtained in the second step after removing the AAO layer formed in the first anodizing step, during which hexagonally ordered, concave-pored Al surface is formed so as to serve as vertical pore nucleation sites for the subsequent anodization step. Although such a two-step anodization process has proven useful for bulk Al surface, the relatively large amount of Al material that needs to be used up to obtain a well ordered AAO template is an issue when the starting material is a thin film layer of Al rather than a bulk Al foil. In this paper, we demonstrate successful fabrications of ordered and vertically aligned AAO nanopore patterns directed by a hexagonally patterned poly(styrene-b-4-vinylpyridine) di-block copolymer layer place...