W. S. Chen

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

Nitride-based LEDs with an insulating SiO2 layer underneath p-pad electrodes

We proposed a simple method to reduce the current crowding effect of nitride-based light emitting diodes (LEDs) without extra dry etching and refill. It was found that we can achieve much better current spreading by inserting an insulating SiO 2 layer between the epitaxial layer and the p-pad electrode. It was also found that we can enhance light output intensity by 22%. Furthermore, it was found that 20 mA forward voltage only increased slightly from 3.32 to 3.37 V with the insertion of the SiO 2 layer. The reliability of the proposed LED is also good.

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 p-i-n sensors with indium-tin-oxide electrodes on Mg-doped AlGaN/GaN strain layer superlattice structure were fabricated and characterized. It was found that the fabricated sensors exhibit small dark current and large reverse breakdown voltage. With an incident wavelength of 355 nm, we achieved a peak responsivity of 0.17 A/W which corresponds to 59% external quantum efficiency for sensors with 500/spl deg/C annealed ITO(70 nm) p-contacts.

DBR Backside Reflector

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

GaN-based p-i-n sensors with ITO contacts

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

The properties of indium-tin-oxide (ITO)/Ni films as transparent ohmic contacts of nitride-based flip chip (FC) light emitting diodes (LEDs) were studied. It was found that 300degC rapid thermal annealed (RTA) ITO(15 nm)/Ni(1 nm) could provide good electrical and optical properties for FC LED applications. It was also found that 20-mA operation voltage and output power of the 465-nm FC LEDs with ITO/Ni/Ag reflective mirror were 3.16 V and 21 mW, respectively. Furthermore, it was found that output intensity of the proposed LED only decayed by 5% after 1200 h under 30-mA current injection at room temperature.

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

A power light-emitting diode (LED) module has been successfully designed and demonstrated by combining GaN-based power LEDs with CMOS electrostatic discharge (ESD) protection circuits through a flip-chip process. It was found that we could enhance the power LED output intensity by 20% by using the flip-chip technology. Lifetimes of flip-chip power LEDs were also found to be better. It was also found that the use of CMOS ESD protection circuits did not degrade the output intensity and lifetime of flip-chip power LEDs. Furthermore, it was found that we could not only significantly enhance the reverse ESD characteristics but could also enhance the positive ESD characteristics of nitride-based LEDs by using the CMOS ESD protection circuits.

Highly Reliable High-Brightness GaN-Based Flip Chip LEDs

Nitride-based flip-chip (FC) light-emitting diodes (LEDs) emitting at 465 nm with Ni transparent ohmic contact layers and Ag reflective mirrors were fabricated. With an incident light wavelength of 465 nm, it was found that transmittance of normalized 300/spl deg/C rapid thermal annealed (RTA) Ni(2.5 nm) was 93% while normalized reflectance of 300/spl deg/C RTA Ni(2.5 nm)/Ag(200 nm) was 92%. It was also found that 300/spl deg/C RTA Ni(2.5 nm) formed good ohmic contact on n/sup +/ short-period-superlattice structure with specific contact resistance of 7.8/spl times/10/sup -4/ /spl Omega//spl middot/cm/sup 2/. With 20-mA current injection, it was found that forward voltage and output power were 3.15 V and 16.2 mW for FC LED with 300/spl deg/C RTA Ni(2.5 nm)/Ag(200 nm). Furthermore, it was found that reliabilities of FC LEDs were good.