C. F. Shen

Nitride-based flip-chip ITO LEDs

Nitride-based flip-chip indium-tin-oxide (ITO) light-emitting diodes (LEDs) were successfully fabricated. It was found that the forward voltage and the 20 mA output power of the flip-chip ITO LED were 3.32 V and 14.5 mW, respectively. Although the operation voltage of such a flip-chip ITO LED was slightly larger, it was found that its output power was much larger than those of conventional nonflip-chip LEDs. It was also found that flip-chip ITO LEDs were more reliable.

Nitride-based light emitting diodes with indium tin oxide electrode patterned by imprint lithography

The authors propose a simple, low cost, and mass producible imprint lithography method to texture indium tin oxide (ITO) contact layer of nitride-based light emitting diodes (LEDs). Under 20mA current injection, it was found that forward voltages were 3.24, 3.25, and 3.24V while the LED output powers were 11.7, 12.6, and 13.3mW for the conventional ITO LED, ITO LED patterned with 1.75μm holes, and ITO LED patterned with 0.85μm holes, respectively.

Nitride-Based High-Power Flip-Chip LED With Double-Side Patterned Sapphire Substrate

A nitride-based high-power flip-chip (FC) light-emitting diode (LED) with a double-side patterned sapphire substrate (PSS) was proposed and realized. Under 350-mA current injection, it was found that forward voltages were 3.24, 3.26, and 3.25 V for the conventional FC LED, FC LED prepared on PSS, and FC LED with double-side PSS, respectively. It was found that the 350-mA LED output powers were 79.3, 98.1, and 121.5 mW for the conventional FC LED, FC LED prepared on PSS, and FC LED with double-side PSS, respectively. In other words, we can enhance the electroluminescence intensity by 53% without increasing operation voltage of the fabricated LED

Improved Performance of GaN-Based Blue LEDs With the InGaN Insertion Layer Between the MQW Active Layer and the n-GaN Cladding Layer

In this study, we demonstrate the effect of GaN-based blue light-emitting diodes (LEDs), using an InGaN layer inserted between the n-type GaN cladding layer and the active layer (InGaN/GaN multiple quantum well), on improving device performances. With a 20-mA current injection, the results indicate that the typical output power (or forward voltage) of light-emitting diodes grown with, and without, the InGaN insertion layer are approximately 18.1 (3.1) and 15.3(3.5) mW (V), respectively. This corresponds to an enhancement in output power (wall-plug efficiency) of around 18% (33%), with the use of the InGaN insertion layer. In addition, the electrostatic discharge (ESD) endurance voltages increased from 1000 V to 6000 V when the InGaN insertion layer was applied to the GaN/sapphire-based LEDs. The improvement of output power and ESD endurance voltage could be mainly due to the fact that the Si-doped InGaN insertion layer played the role of a current-spreading layer, which led to a lower possibility of junctions suffering a large current density in specific local sites.

Nitride-Based LEDs With a Hybrid Al Mirror

Nitride-based light-emitting diodes (LEDs) with a hybrid backside reflector combining a TiO2/SiO2 distributed Bragg reflector (DBR) and an Al mirror were proposed and realized. It was found that we can significantly enhance the 35% reflectivity of the 2-pair TiO2/SiO2 DBR to 94% by combining with Al mirror (hybrid reflector). Furthermore, reflectivity of the proposed reflector depends only slightly on incident light wavelength and the incident angle. With 350-mA current injection, it was found that the output powers were 145.7, 178.2, and 201.9 mW for the LEDs with 2-pair DBR, with an Al mirror and with a hybrid reflector, respectively, when packaged in TO-cups. It was also found that reliability for the LED with the hybrid reflector is good.

+ {\hbox {TiO}} _{2} /{\hbox {SiO}}_{2}

Nitride-based flip-chip light-emitting diodes (LEDs) with various transparent ohmic contacts and reflective mirrors were fabricated. At 470 nm, it was found that Ni could provide 92% transmittance while Ag could provide 92.4% reflectively. It was also found that the 20-mA forward voltages measured from LEDs with Ni+Ag, Ni+Al, and Ni+Pt were 3.15, 3.29, and 3.18 V while the output powers were 16, 13.3, and 11.6 mW, respectively. Furthermore, it was found that lifetimes of the fabricated flip-chip LEDs were good

DBR Backside Reflector

Nitride-based light emitting diodes (LEDs) with sidewall texture and pillar waveguides (STPW) were fabricated using conventional lithography method. With 20-mA injection current, it was found that forward voltages were 3.16 and 3.15 V for the conventional LED and the LED with STPW, respectively. It was also found that 20-mA LED output powers were 8.4 and 10.1 mW for conventional LED and the LED with STPW, respectively. The enhancement is attributed to the out-coupling of lateral waveguide mode in the near horizontal directions

Nitride-based flip-chip LEDs with transparent Ohmic contacts and reflective mirrors

Nitride-based large size (i.e. 1 mm×1 mm) indium-tin-oxide (ITO) light emitting diodes (LEDs) were successfully fabricated. In order to enhance the output intensity of power chips, Al reflector was deposited by e-beam evaporator on the chip backside. It was found that the 350 mA output power was 84.8 mW (W-P-E=7.2%) at 460 nm for the power chip with ITO as p-contacts and Al as back-side reflector. It was also found that ITO power chip with Al reflector was more reliable.

Nitride-Based Light Emitting Diodes With Textured Sidewalls and Pillar Waveguides

Al0.2Ga0.8N/GaN Schottky-barrier ultraviolet (UV)-B bandpass photodetectors (PDs) with indium–tin–oxide (ITO) contact on low-temperature (LT)-GaN cap layers were fabricated and characterized. It was found that dark currents of our PDs were low due to the highly resistive LT GaN cap layers. It was also found that we can realize UV-B PDs with different bandwidths by controlling thickness and annealing conditions. The detectivity, D ∗ , of the PDs with ITO contacts was also larger than the conventional PDs with Ni/Au contacts.

Nitride based Power Chip with Indium-Tin-Oxide p-Contact and Al Back-Side Reflector

Nitride-based light-emitting diodes (LEDs) with internal electrostatic-discharge (ESD) protection diodes emitting at 460 nm were proposed and realized. By building an internal GaN p-n junction diode, a negative ESD-induced pulse current is expected to flow through the protection diode without damaging the major LED. The ESD characteristic of the fabricated LEDs was obviously improved with this design. Furthermore, the dimension of the internal p-n diode would influence the capacity for tolerating the ESD stress. It was found that a negative ESD threshold could be significantly increased from 300-400 to 2000 V. On the other hand, the authors managed to bring down the 20-mA operation voltage to 3.29 V using the n-metal finger, which entails a good current spreading under operation as the result of a reduced current-crowding effect. Since a good current spreading beneficially alleviates the thermal effect under long-term operation, an effective pattern layout design clearly would also prolong the lifetime of the proposed LEDs