Kwang Ki Choi

Wafer-level fabrication of GaN-based vertical light-emitting diodes using a multi-functional bonding material system

We first report on the fabrication of 2 inch wafer-level GaN-based vertical light-emitting diodes (LEDs) by using a multi-functional bonding material system, which is composed of a thick Cu diffusion barrier and a bonding layer. The bonding material system superbly absorbs laser-induced stress and also effectively serves as a barrier to the indiffusion of Sn to the active region. Fully packaged vertical LEDs fabricated with indium tin oxide (ITO)/AgCu contact and the bonding material system give an operating voltage of 3.35 V at 350 mA. After over 1800 h, the operating voltages remain stable, and the reverse currents are in the range 3–8 × 10−7 A at −5 V.

Design of high-efficiency GaN-based light emitting diodes with vertical injection geometry

The authors report on the design and fabrication of high-efficiency GaN-based light emitting diodes (LEDs) with vertical-injection geometry. Based on the analyses of LED test patterns fabricated with various n-electrode dimensions, a design rule for vertical LEDs is proposed. It is found that the suppression of the vertical current under n electrodes and the efficient injection of the spreading current across the n layers are essential to fabricate high-efficiency LEDs. Introduction of the current blocking layer along with well-designed branched n electrodes results in a large enhancement of power efficiency by a factor of 1.9, compared with that of reference LEDs.

Improvement of the Light Output Power of GaN-Based Vertical Light Emitting Diodes by a Current Blocking Layer

The light output characteristics of GaN-based vertical light emitting diodes (1 ×1 mm) fabricated by the multifunctional bonding material system have been investigated as a function of the linewidth of a SiO 2 current blocking layer (CBL). As the CBL width increases from 0 to 20 μm, the forward voltage increases from 2.82 to 2.88 V at 350 mA, whereas the reverse leakage current decreases from 4.90 × 10 -7 to 3.05 × 10 -7 A at -10 V. The output power increases with increasing CBL linewidth. Furthermore, the output power of all the samples continuously increases without saturation across the current range of 0-1000 mA.

Improved Electrostatic Discharge Protection in GaN-Based Vertical Light-Emitting Diodes by an Internal Diode

We first fabricated GaN-based vertical light-emitting diodes (LEDs) with electrostatic discharge (ESD) protection internal diode. Despite the reduced emitting area due to the internal diode, the LEDs with the internal diode give a forward voltage of 3.42 V at 350 mA similar to that (3.40) of LEDs without the internal diode. It is shown that the output power of the LEDs with the internal diode is reduced by about 6% at 350 mA compared to reference LEDs without the internal diode. It is, however, further shown that the LEDs without the internal diode give a yield of 0% at the reverse voltages above 400 V, while the LEDs with the internal diode show a yield of ~ 90% at reverse voltages of 2-4 kV.

Effect of oxygen plasma-induced current blocking on the performance of GaN-based vertical light-emitting diodes

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 charac...

Fabrication of High Performance GaN-Based Vertical Light-Emitting Diodes Using a Transparent Conducting Indium Tin Oxide Channel Layer

We fabricate blue GaN-based vertical light-emitting diodes (LEDs) using transparent insulating SiO 2 and conducting indium tin oxide (ITO) channel layers connected to the passivation layer by a combined process of electroplated deposition and a laser lift-off technique. It is shown that unlike the SiO 2 layer, the ITO layer effectively serves as current spreading and injection layers. LEDs fabricated with the ITO channel layer exhibit a slightly higher reverse current when the voltage exceeds ―10 V. However, LEDs fabricated with the ITO layer produce higher output power (by ∼20% at 100 mA) compared to LEDs with the SiO 2 layers.

Improved Output Power of GaN-Based Vertical Light Emitting Diodes Fabricated with Current Blocking Region Formed by O2 Plasma Treatment

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 plasma-treated LEDs is degraded by less than 2% of the initial value after 500 h.