Light emitting diodes reliability review

Recent advances in ultraviolet photodetectors

Microstructures produced during the epitaxial growth of InGaN alloys

We report a dramatic increase in the light extraction efficiency of GaN-based blue light-emitting diodes(LEDs) by ZnOnanorod arrays on a planar indium tin oxide (ITO) transparent electrode.ZnOnanorods were grown into aqueous solution at the low temperature of 90 ° C . With 20 mA current injection, the light output efficiency of the LED with ZnOnanorod arrays on ITO was increased by about 57% with no increase in a forward voltage over the conventional LEDs with planar ITO. The increased light extraction by the ZnOnanorod arrays is due to the formation of sidewalls and a rough surface, resulting in a multiple photon scattering at the LEDsurface.

Enhanced light extraction efficiency of GaN-based light-emitting diodes with ZnO nanorod arrays grown using aqueous solution

In this letter, metal-semiconductor-metal (MSM) TiO2 ultraviolet (UV) detectors with Ni electrodes have been fabricated. TiO2 thin films were prepared by sol-gel method. At 5 V bias, the dark current of the detector with Ni electrode was 1.83 nA. High photoresponse of 889.6 A/W was found under irradiation of 260 nm UV light, which was much higher than those of other wide bandgap UV detectors with MSM structure. The high photoresponse was due to the great internal gain caused by the hole trapping at interface. The rise time of the device was 13.34 ms and the fall time was 11.43 s.

/pdf/metal-semiconductor-metal-tio2-ultraviolet-detectors-with-ni-2zooirzdk1.pdf

Metal-semiconductor-metal TiO2 ultraviolet detectors with Ni electrodes

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.

/pdf/nitride-based-light-emitting-diodes-with-indium-tin-oxide-48d3ckc6o6.pdf

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

In this letter, a GaN/sapphire light-emitting diode (LED) structure was designed with improved electrostatic discharge (ESD) performance through the use of a shunt GaN ESD diode connected in inverse-parallel to the GaN LED. Thus, electrostatic charge can be discharged from the GaN LED through the shunt diode. We found that the ESD withstanding capability of GaN/sapphire LEDs incorporating this ESD-protection feature could be increased from several hundreds up to 3500 V in the human body model. Furthermore, flip-chip (FC) technology was also used to produce ESD-protected LEDs to further improve light output power and reliability. At a 20-mA current injection, the output power of the FC LEDs showed an improvement of around 60%. After a 1200-h aging test, the luminous intensities of the FC LEDs featuring an internal ESD-protection diode decreased by 4%. This decay percentage was far less than those of non-FC LEDs

Improved Reliability and ESD Characteristics of Flip-Chip GaN-Based LEDs With Internal Inverse-Parallel Protection Diodes

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.

/pdf/nitride-based-leds-with-an-insulating-sio2-layer-underneath-3hycwdzj4u.pdf

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

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.

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

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.

C. F. Shen

Papers

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

Improved Reliability and ESD Characteristics of Flip-Chip GaN-Based LEDs With Internal Inverse-Parallel Protection Diodes

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

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

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