Wei Chih Peng

Improved luminance intensity of InGaN–GaN light-emitting diode by roughening both the p-GaN surface and the undoped-GaN surface

The InGaN–GaN epitaxial films were grown by low-pressure metal-organic chemical vapor deposition on a sapphire substrate, and then the light-emitting diode (LED) with double roughened (p-GaN and undoped-GaN) surfaces was fabricated by surface-roughening, wafer-bonding, and laser lift-off technologies. It was found that the front side luminance intensity of double roughened LED was 2.77 times higher than that of the conventional LED at an injection current of 20mA. The backside luminance intensity was 2.37 times higher than that of the conventional LED. This is because the double roughened surfaces can provide photons multiple chances to escape from the LED surface, and redirect photons, which were originally emitted out of the escape cone, back into the escape cone.

Effects of laser sources on the reverse-bias leakages of laser lift-off GaN-based light-emitting diodes

The KrF pulsed excimer laser (248nm) and the frequency-tripled neodymium doped yttrium aluminum garnet laser (355nm) have been used to separate GaN thin films from sapphire substrates and transfer to bond other substrate. However, these processes would increase the dislocation density, resulting in an increase of the leakage current. In this study, the effects of these two laser sources on the reverse-bias leakages of InGaN–GaN light-emitting diodes were studied.

Enhanced performance of an InGaN-GaN light-emitting diode by roughening the undoped-GaN surface and applying a mirror coating to the sapphire substrate

An InGaN–GaN light-emitting diode (LED) with a roughened undoped-GaN surface and a silver mirror on the sapphire substrate was fabricated through a double transfer method. It was found that, at an injection current of 20mA, its luminance intensity was 100% larger than conventional LEDs. Its output power was 49% larger than conventional LEDs.

Performance of InGaN-GaN LEDs fabricated using glue bonding on 50-mm Si substrate

Vertical InGaN-GaN light-emitting diodes (LEDs) epitaxial films were successfully fabricated on a 50-mm Si substrate using glue bonding and laser liftoff technology. A high-temperature stable organic film, rather than a solder metal, was used as the bonding agent. It was found that the light output of the vertical InGaN LED chip exceeded that of the conventional sapphire-substrate LEDs by about 20% at an injection current of 20 mA. The vertical InGaN LEDs operated at a much higher injection forward current (280 mA) than sapphire-substrate LEDs (180 mA). The radiation pattern of the vertical InGaN LEDs is more symmetrical than that of the sapphire-substrate LEDs. Furthermore, the vertical InGaN LEDs remain highly reliable after 1000 h of testing

High-power AlGaInP light-emitting diodes with metal substrates fabricated by wafer bonding

High-power light-emitting diodes (LEDs) fabricated on Cu substrates were investigated in this study. The AlGaInP LED structure was bonded to a Cu substrate by using indium-tin-oxide as the diffusion barrier layer. It was found that Cu-substrate-bonded LED devices could be operated in a much higher injection forward current, 800 mA, which was eight times higher than that used in traditional GaAs-substrate LEDs. The luminous intensity of the Cu-substrate LEDs could reach as high as 1230 mcd, which was three times higher than that of the GaAs-substrate LEDs.

Effects of Laser Sources on Damage Mechanisms and Reverse-Bias Leakages of Laser Lift-Off GaN-Based LEDs

In this study, three types of LEDs were investigated. Samples designated as “CV-LED” were conventional LEDs without any laser treatment. Samples designated as “KrF-LED” were CV-LEDs treated with KrF pulsed excimer laser, while “YAG-LEDs” were CV-LEDs treated with Nd:YAG laser. The basic fabrication processes of these LEDs were almost the same. 7 The LED structures were grown by low pressure metallorganic chemical vapor deposition. The structures comprised a 5 nm thick Si-doped n + -InGaN layer, a 400 nm thick Mg-doped p-GaN layer, an InGaN‐GaN multiple quantum well MQW ,a2 m thick Si-doped n-GaN layer, a 2 m thick undoped-GaN layer film, and a buffer layer on the sapphire substrate. For the CV-LED, the device mesa with a chip size of 350 350 m was defined by an inductively coupled plasma which removed the Mg-doped GaN and MQW until the Si-doped GaN was exposed. Then, the indium tin oxide ITO layer was deposited on the n + -InGaN layer using an E-beam coater to form a p-side contact layer and a current spreading layer. The Cr/Au layer was deposited onto the ITO layer to form the p- and n-side electrodes. The fabrication processes of KrF-LED and YAG-LED are shown in Fig. 1. Before the LLO process, the CV-LED wafer was bonded to a host substrate covered with an adhesive/glue layer, and the sapphire substrate of KrF-LED was polished using a diamond paper. The KrF laser beam spot size of 700 700 m four chips were lifted off in etch pulse was scanned without overlap from pulse to pulse. The 355 nm Nd:YAG LLO system was constructed by a series of lens, the laser beam was near circle shape, and the lateral energy of the converged laser beam was a Gaussian distribution. The Nd:YAG laser beam spot size of 500 m was scanned with a 20% overlap from pulse to pulse. The pulse length of the KrF laser was 35 ns, which was longer than that of the YAG laser 5n s. The energy densities of the KrF laser were in the range between 700 and 1000 mJ/cm 2 , while those of the YAG laser were in the range between 100 and 400 mJ. These wafers were then bonded to a sapphire substrate with an adhesive layer at 200°C for 60 min with a comprehensive load of 10 kg/cm 2 . The host substrate and glue layer were subsequently removed.

Enhanced Light Output in Double Roughened GaN Light-Emitting Diodes via Various Texturing Treatments of Undoped-GaN Layer

An InGaN–GaN light-emitting diodes (LEDs) with double roughened (p-GaN and undoped-GaN) surfaces were successfully fabricated by surface-roughening, wafer-bonding and laser lift-off technologies. The effect of the roughness of the undoped-GaN layer on the performance of double roughened LEDs was investigated. It was found that the rms roughness of the undoped-GaN layer increased from 18.6 to 146.7 nm, the output power increased from 7.2 to 10.2 mW, and view angle decreased from 133.6 to 116°.