Shi-Ming Chen

ESD engineering of nitride-based LEDs

GaN-based light emitting diodes (LEDs) with p-cap layers grown at various temperatures were fabricated. It was found that the LED with 900/spl deg/C-grown p-cap layer could only endure negative 1100 V electrostatic discharge (ESD) pulses while the LED with 1040/spl deg/C-grown p-cap layer could endure ESD pulses as high as negative 3500 V. It was also found that the ESD performances of the LEDs with 900 and 1040/spl deg/C-grown p-cap layers were limited by the V-shape defects and the bonding pad design, respectively.

GaN-Based Light-Emitting Diodes Grown on Photonic Crystal-Patterned Sapphire Substrates by Nanosphere Lithography

GaN-based light-emitting diodes (LEDs) grown on photonic crystal-patterned sapphire substrates (PCPSS) have been demonstrated. PCPSS was fabricated by nanosphere lithography, and the photonic crystal structure was the hexagonal-lattice pattern. The forward voltages of PCPSS and patterned sapphire substrates (PSS) LEDs were smaller than that of conventional sapphire substrates (CSS) LED, and it infers the epitaxial film quality of PCPSS and PSS LEDs has been slightly improved. The luminance intensity of PCPSS LED was 1.63 and 1.51 times higher than those of CSS and PSS LED at 20 mA injection current. The enhancement in the luminance intensity of PCPSS LED is attributed to the photonic crystal structure.

Nitride-based MQW LEDs with multiple GaN-SiN nucleation layers

Nitride-based light emitting diodes (LEDs) separately prepared with a conventional single low-temperature (LT) GaN nucleation layer and multiple GaN-SiN nucleation layers were both prepared. It was found that we could reduce defect density and thus improve crystal quality of the GaN-based LEDs by using multiple GaN-SiN nucleation layers. With a 20-V applied reverse bias, it was found that the reverse leakage currents measured from the LED with a single LT GaN nucleation layer and the one with 10-pair GaN-SiN nucleation layers were 1.5/spl times/10/sup -4/ and 2.5/spl times/10/sup -6/ A, respectively. It was also determined that we could use the multiple GaN-SiN nucleation layers to enhance the output intensity of near ultraviolet (UV) LEDs and to improve the reliability of nitride-based LEDs.

Dependence of ZnO films on sputtering parameters and saw device on ZnO/InP

Abstract To compensate the piezoelectrical properties of InP-based material for the applications of monolithic acousto-optic devices and systems, a high quality ZnO film with a highly preferred orientation and fine structure should be deposited onto on InP substrate. The dependence of the quality of ZnO films on RF sputtering parameters was investigated. The optimal deposition conditions are obtained as substrate temperature of 250°C, sputtering power of 350 W, and oxygen content of 20 vol%. A SAW device with center frequency of 105 MHz fabricated on the ZnO/InP was demonstrated.

Thermal management and novel package design of high power light-emitting diodes

Thermal management and package materials in high power light emitting diodes (HPLEDs) are now critical design issues to limit their luminous intensity, reliability, and applications. In this paper electroless and electroplating techniques (EET) were both applied in fabrication of the red, green, and blue HPLEDs (RGB HPLEDs) chips. The HPLEDs with conventional package structures were fixed on the lead frames by adhesives, but the HPLEDs using EET were fixed on copper substrates without any adhesive resin. In our work, the results show that the thermal resistance of HPLED using EET is much less than one of the HPLED using adhesive resin. The maximum luminous intensity of the single chip HPLED using EET is larger than HPLED with resin/MCPCB (metal core printed circuit board) in room temperature.

InGaN/GaN Light Emitting Diodes with a Lateral Current Blocking Structure

The light output of InGaN/GaN light-emitting diodes (LEDs) was improved by introducing a current blocking hole between the n-type and p-type bonding pads. The injected current was forced to spread out instead of directly passing along the nearest path between the p-type and n-type bonding pads. The light output of the LED with a current blocking hole at 20 mA was 7.2% higher than that of the conventional LED. The forward voltage of the LED with the blocking hole was 3.29 V at 20 mA, which is slightly higher than that of the conventional LED (3.26 V). LEDs with different current blocking hole sizes were also studied.

Two-mode InGaSb/GaSb strained-layer superlattice infrared photodetector

An interesting two-mode photodetector was constructed using an In/sub 0.19/Ga/sub 0.81/Sb/GaSb strained-layer superlattice (SLS). Such a structure is, at the same time, of type I for heavy hole and type II for light hole. The mini-subbands of this In/sub 0.19/Ga/sub 0.81/Sb/GaSb SLS are calculated using the modified Kronig-Penney model, as a function of well width at 300 K. A ten-period In/sub 0.19/Ga/sub 0.81/Sb/GaSb SLS structure can be applied as a two-mode photodetector with near-zero and reverse bias. This phenomenon can be proved by the spectral response of the structure grown by low-pressure metalorganic chemical vapor deposition (MOCVD). The wavelengths of dominant absorption peaks are 1.92 and 1.77 mu m at near-zero and reverse bias, respectively. The experimental data are in good agreement with the theoretical deductions.<<ETX>>

Nitride-based LEDs with MQW active regions grown by different temperature profiles

Nitride-based light-emitting diodes (LEDs) with multiple quantum-well active regions were separately prepared by metal-organic vapor phase epitaxy in different temperature profiles. Compared with conventional samples, the reduced reverse leakage current and improved electrostatic discharge characteristics of the LEDs can both be achieved using temperature ramping and temperature cycling methods. However, using the temperature ramping may degrade the optical properties of devices due to desorption of In atoms and/or impurity incorporation. With an emission wavelength of 465 nm, the 20-mA output powers measured were 5.5, 6.0, and 7.9 mW for temperature ramping LED, conventional LED, and temperature cycling LED, respectively.

AlGaInP Light Emitting Diode with a Modulation-Doped Superlattice

AlGaInP light-emitting diode (LED) with a GaP/In0.5Ga0.5P modulation-doped superlattice was grown by metal organic chemical vapor deposition (MOCVD). The luminous intensity was increased by a factor of 1.16 at 20 mA and of 1.5 at 100 mA with the benefit of the modulation-doped superlattice. The enhanced current-spreading ability offered by the modulation-doped superlattice was demonstrated by the analysis of dynamic resistance under different operation voltage. In addition, the superior current spreading also brought about less generation of heat, which can be manifested by the electroluminescence (EL) spectrum with increase of the injection current.

Improvement of AlGaInP Multiple-Quantum-Well Light-Emitting Diodes by Modification of Ohmic Contact Layer

A meshed contact layer was proposed to enhance the current-spreading ability of AlInGaP light-emitting diodes (LEDs). Via the modification of the contact layer, the luminous intensity was increased by a factor of 1.16 compared with that of the conventional LEDs at a wavelength of 570 nm. Moreover, the brightness reliability of such a new structure was found to be superior to that of conventional structures.