Hyun Gi Hong

Enhancement of the light output of GaN-based ultraviolet light-emitting diodes by a one-dimensional nanopatterning process

We have demonstrated the enhancement of the output power of ultraviolet GaN-based light-emitting diodes (LEDs) by using one-dimensionally nanopatterned Cu-doped indium oxide(CIO)/indium tin oxide (ITO) p-type contact layers. The one-dimensional (1D) nanopatterns (250nm in width and 100nm in depth) are defined using a TiO2 1D nanomask fabricated by means of a surface relief grating technique. When fabricated with the nanopatterned p-contact layers, the output power of LEDs is improved by 40 and 63% at 20mA as compared to those fabricated with the unpatterned CIO/ITO and conventional Ni∕Au contacts, respectively.

Highly Reflective and Low Resistance Indium Tin Oxide/Ag Ohmic Contacts to p-Type GaN for Flip-Chip Light Emitting Diodes

Highly Reflective and Low Resistance Indium Tin Oxide/Ag Ohmic Contacts to p-Type GaN for Flip-Chip Light Emitting Diodes Woong-Ki Hong,* June-O Song, Hyun-Gi Hong, Keun-Yong Ban, Takhee Lee, J. S. Kwak, Y. Park, and Tae-Yeon Seong Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea School of Electric and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0250, USA Department of Materials Science and Metallurgical Engineering, Sunchon National University, Chonnam 540-742, Korea Samsung Advanced Institute of Technology, Photonics Laboratory, Suwon 440-600, Korea

Enhanced light output of GaN-based near-UV light-emitting diodes by using nanopatterned indium tin oxide electrodes

We report on the enhancement of the light output of near-UV (298 nm) GaN-based light-emitting diodes (LEDs) by using nanopatterned indium tin oxide (ITO) p-type contact layers. One-dimensional (1D) and two-dimensional (2D) nanopatterns are defined using a TiO2 nano-mask, fabricated by means of a surface relief grating technique. The LEDs fabricated with the 1D and 2D nanopatterned p-type electrodes produce higher output powers by 33–48% (at 20 mA) as compared to those fabricated with the unpatterned contacts. The pattern-induced improvement of the output power is described in terms of the formation of the sidewalls of p-type electrodes.

In/ITO p-Type Electrode for High-Brightness GaN-Based Light Emitting Diodes

Indium interlayers (10 nm thick) were used to form highly transparent and low-resistance indium-tin oxide (ITO) (200 nm) ohmic contacts to p-GaN for high-brightness light emitting diodes (LEDs). The In/ITO contacts became ohmic with a specific contact resistance of 1.46 × 10 -3 Ω cm 2 and produced transmittance of 95.8% at wavelength of 460 nm when annealed at 530°C. Blue LEDs fabricated with the annealed In/ITO p-type contact layers exhibited a forward-bias voltage of 3.42 V at an injection current of 20 mA. The light output power of LEDs with the In/ITO contacts was enhanced 91% at 20 mA compared to LEDs with the oxidized Ni/Au contacts.

Possible Ohmic Mechanisms of Ag/Indium Tin Oxide p-Type Contacts for High-Brightness GaN -Based Light Emitting Diodes

We have investigated the Ag (1 nm)/indium tin oxide (ITO) (200 nm) contacts by scanning transmission electron microscopy (STEM), Auger electron spectroscopy (AES), and X-ray photoemission spectroscopy (XPS) to understand its ohmic mechanism. The Ag/ITO contacts exhibit ohmic behaviors, when annealed at 400-600°C. The effective Schottky barrier heights depend on the annealing temperatures. STEM and AES results reveal the formation of Ag nanodots (5-35 nm across) and Ga-Ag solid solution. Based on the STEM, AES, and XPS results, the ohmic contact formation is described in terms of the formation of the Ga-Ag solid solution and the inhomogeneous interfaces with nanodots.

Low resistance and highly reflective Sb-doped SnO2/Ag ohmic contacts to p-type GaN for flip-chip LEDs

We have investigated high-quality Sb-doped SnO 2 /Ag ohmic contacts to p-GaN for use in flip-chip light emitting diodes (LEDs). The Sb-doped SnO 2 /Ag contacts produce specific contact resistances of ∼10 - 4 Ω cm 2 upon annealing at 430 and 530°C for 1 min in air. It is shown that InGaN blue LEDs fabricated with the Sb-doped SnO 2 /Ag contacts give a forward-bias voltage of 3.18 V at 20 mA, while LEDs with Ag contacts show 3.36 V. It is further shown that the LEDs made with the Sb-doped SnO 2 /Ag contact layers show higher light output power compared with the LEDs with the Ag contacts.

Effects of Oxygen Partial Pressure on the Electrical and Optical Properties of Pulsed-Laser-Deposited Sb-Doped SnO2 Films

We have investigated the electrical and optical properties of pulsed-laser-deposited Sb-doped SnO 2 films (250 nm thick) as a function of the oxygen partial pressure. The SnO 2 films were grown on glass substrates using a SnO 2 target containing 5 atom % Sb. The distance between the substrate and the target was 7 cm and working pressure varied from 1.1 to 13.3 Pa. The target was ablated using KrF excimer laser with energy density of 3.75 J/cm 2 . It is shown that the electrical and optical properties of the films grown at 480°C with 3000 pulses sensitively depend on the oxygen pressure. The electron concentration is maximum (5.6 X 10 20 cm -3 ) at 4 Pa, the electron mobility is maximum (8.5 cm 2 V -1 s -1 ) at 9.3 Pa, and the resistivity is minimum (2.5 X 10 -3 Ω cm) at 4 Pa. The transmittance is shown to depend on the oxygen pressures. X-ray diffraction results show that the crystalline quality of the films becomes improved with decreasing oxygen pressure. It is further shown that the sample grown at 1.1 Pa contains oxygen-deficient phases. The UV absorption edge of the films shifts toward the shorter wavelengths with decreasing oxygen pressure, which is attributed to Burstein-Moss shift.

Formation of Sb-doped SnO2 p-type ohmic contact for Near-UV GaN-based LEDs by a CIO interlayer

A Cu-doped In 2 O 3 (CIO) interlayer was introduced to enhance the electrical and optical properties of Sb-doped SnO 2 (ATO) p-type electrodes grown by pulsed laser deposition. CIO (2.5 nm)/ATO (250 nm) contacts become ohmic with specific contact resistance of 2.1 × 10 -3 Ω cm 2 and give transmittance of ∼81% at 400 nm, when annealed at 630°C for 1 min in air. Near-UV (400 nm) GaN-based light-emitting diodes (LEDs) fabricated with the CIO/ATO p-electrodes give forward-bias voltage of 3.91 V at injection current of 20 mA and show much higher output power compared to LEDs with conventional Ni/Au p-electrodes.

Use of an indium zinc oxide interlayer for forming Ag-based Ohmic contacts to p-type GaN for UV-light-emitting diodes

We have investigated indium-doped ZnO(IZO)/Ag Ohmic contacts to p-type GaN for use in UV-light-emitting diodes (LEDs). The as-deposited sample shows rectifying behaviour. However, the samples become Ohmic when annealed at temperature of 330–530 °C for 1 min in air. For example, the contact produces specific contact resistance of 5.51 × 10−4 Ω cm2 upon annealing at 530 °C. In addition, the 530 °C annealed IZO/Ag contacts give reflectance of 82.3% at a wavelength of 405 nm, which is better than that (70.6%) of the single Ag contacts. Near-UV LEDs fabricated with the IZO/Ag contacts give forward voltage of 3.24 V at an injection current of 20 mA, which is better than that with the single Ag contacts. On the basis of x-ray photoemission spectroscopy and scanning transmission electron microscopy results, possible Ohmic formation mechanisms are described.

Reflective and Low-Resistance Zn ∕ Rh Contacts to p-Type GaN for Flip-Chip Light-Emitting Diodes

Reflective and Low-Resistance Zn/Rh Contacts to p-Type GaN for Flip-Chip Light-Emitting Diodes June-O Song, Woong-Ki Hong, Hyun-Gi Hong, Kyoung-Kook Kim, Takhee Lee, and Tae-Yeon Seong* Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8586, Japan