Chip Development Group

Paju, South Korea

Chip Development Group

Paju, South Korea
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Park S.-H.,Korea University | Jeon J.-W.,Korea University | Seong T.-Y.,Korea University | Oh J.-T.,Chip Development Group
Journal of the Korean Physical Society | Year: 2011

We investigated Rh-Zn solid solution (3 nm)/Ag(200 nm) schemes in order to produce thermally stable and low-resistance p-type Ohmic reflectors for high-performance flip-chip light-emitting diodes (LEDs). The Rh-Zn solid solution/Ag contacts show a specific contact resistance of 1.2 × 10-4 Ωcm2 and a reflectance of about 78% at a wavelength of 395 nm when annealed at 500 °C for 1 min in air. Scanning electron microscopy results show that unlike Ag only contacts, the Rh-Zn solid solution/Ag contacts experience insignificant morphological degradation even after annealing at 500 °C for 1 min. Near-UV InGaN/GaN LEDs (1200 × 600 μm2 in chip size) fabricated with the annealed Rh-Zn solid solution/Ag reflectors give a forward-bias voltage of 3.43 V at an injection current of 80 mA, which is lower than that (3.65 V) of LEDs with Ag only reflectors. LEDs with the annealed RhZn solid solution/Ag reflectors exhibit 43% higher light output power (at 80 mA) than the LEDs with annealed Ag contacts. X-ray photoemission spectroscopy examinations were performed to investigate possible Ohmic formation behaviors.

Jeon J.-W.,Korea University | Lee S.Y.,Chip Development Group | Song J.O.,Chip Development Group | Seong T.-Y.,Korea University
Current Applied Physics | Year: 2012

We investigated the electrical properties of Cr(30 nm)/Al(200 nm) contacts to N-polar n-type GaN for high-performance vertical light-emitting diodes and compare them with those of Ti(30 nm)/Al(200 nm) contacts. Before annealing, both the samples show ohmic behaviors with a contact resistivity of 1.9-2.3 × 10-4 Ωcm2. Upon annealing at 250 °C for 1 min in N2 ambient, the Ti/Al contacts become non-ohmic, while the Cr/Al contacts remain ohmic with a contact resistivity of 1.4 × 10-3 Ωcm2. Based on X-ray photoemission spectroscopy and secondary ion mass spectrometry results, ohmic formation and degradation mechanisms are briefly described and discussed. © 2011 Elsevier B.V. All rights reserved.

Lee S.Y.,Chip Development Group | Choi K.K.,Chip Development Group | Jeong H.H.,Chip Development Group | Kim E.J.,Chip Development Group | And 3 more authors.
Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics | Year: 2011

We investigated the effect of O2 plasma-induced current blocking regions (O2 -CBRs) on the performance of GaN-based vertical light-emitting diodes (VLEDs) as a function of the O2 plasma rf power. The VLEDs fabricated with the O2 -CBRs give forward voltages in the range 3.41-3.48 V at 350 mA, which are slightly higher than those in the case of VLEDs with and without SiO2 current-blocking layers (CBLs). The output powers of VLEDs with O2 -CBRs for rf powers of 50 and 100 W are 400.2 and 399.4 mW, respectively, which are slightly higher than those of the VLEDs with SiO2 CBLs. Indium tin oxide (ITO)-based contacts to p-GaN show rectifying behaviors with Schottky barrier heights of 1.89 and 2.78 eV, when treated at rf powers of 50 and 100 W, respectively. X-ray photoemission spectroscopy (XPS) results show that for the samples treated at 50 W, the Ga 2p core level moves toward the higher binding-energy side as compared to that of the reference sample without plasma treatment. On the basis of the electrical characteristics and XPS results, we state that the O2-CBR effect is due to the generation of donor-like defects at the p-GaN surface. © 2011 American Vacuum Society.

Lee S.Y.,Chip Development Group | Choi K.K.,Chip Development Group | Jeong H.H.,Chip Development Group | Kim E.J.,Chip Development Group | And 5 more authors.
Japanese Journal of Applied Physics | Year: 2011

We report on the formation of current blocking regions by O2 plasma treatment to reduce current crowding at the active region above the p-type electrodes of GaN-based vertical light emitting diodes (LEDs). The forward voltage and reverse current (at -5 V) of the plasma-treated LEDs slightly increase with increasing aging time. The output power (at 350 mA) of the plasma-treated LEDs is enhanced by 26% as compared to that of reference LEDs and is comparable to that of LEDs with SiO2 current blocking layers. It is shown that the output power (at 700 mA) of the plasmatreated LEDs is degraded by less than 2% of the initial value after 500 h. © 2011 The Japan Society of Applied Physics.

Byeon K.-J.,Korea University | Park H.,Korea University | Cho J.-Y.,Korea University | Lee S.-H.,Korea University | And 3 more authors.
Current Applied Physics | Year: 2011

Hexagonal arrays of submicron polymer patterns with a high refractive index were fabricated on a vertical light-emitting diode (LED) device by means of nanoimprint lithography (NIL) to improve the light extraction efficiency. An organic-inorganic hybrid resin containing a polymeric titanium dioxide precursor was spin-coated on the n-GaN top layer of a vertical LED wafer. The coated layer was then imprinted for 10 min with an elastomeric polydimethylsiloxane stamp at 200 °C and 5 atm. The NIL process formed pillar patterns on the n-GaN layer of the vertical LED wafer. The pillar patterns have a high refractive index (n ≈ 2.0) in the visible wavelength range; they also have a diameter of 200 nm and a pitch of 700 nm. The light output power of the patterned vertical LED device is 28% greater than that of a non-patterned vertical LED device with a driving current of 350 mA. The I-V characteristics of the vertical LED device confirm that the patterning process induces no electric degradation. © 2011 Elsevier B.V. All rights reserved.

Byeon K.-J.,University of Michigan | Cho J.-Y.,Korea University | Song J.O.,Chip Development Group | Lee S.Y.,Chip Development Group | Lee H.,Korea University
IEEE Photonics Journal | Year: 2013

A high-brightness GaN-based vertical light-emitting diode (VLED) was demonstrated by introducing a large-area low-cost direct printing process. A hexagonally close-packed micrometer convex array was fabricated on the n-GaN top layer of the VLED by direct printing using a hydrogen silsesquioxane solution and subsequent inductively coupled plasma etching. To confirm that the enhancement of light extraction by this structure, a conventional wet-chemical-etched structure was also fabricated on the n-GaN top layer of the VLED, yielding randomly oriented pyramid structures on the layer. Both VLEDs showed much stronger electroluminescence emission than an unpatterned VLED. However, the micrometer convex array improved the light extraction significantly more than the random pyramid structure owing to its greater ability to enlarge the light escape cone, attributed to its 50°-tapered profile and large extraction area. After chip packaging with silicone encapsulation, the light output power of the micropatterned VLED was 11.4% and 106% greater than those of the wet-etched and unpatterned VLEDs, respectively, under a 350-mA drive current. © 2009-2012 IEEE.

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