Hsu-Hung Hsueh

Pulsed laser deposition of hexagonal GaN-on-Si(100) template for MOCVD applications

Growth of hexagonal GaN on Si(100) templates via pulsed laser deposition (PLD) was investigated for the further development of GaN-on-Si technology. The evolution of the GaN growth mechanism at various growth times was monitored by SEM and TEM, which indicated that the GaN growth mode changes gradually from island growth to layer growth as the growth time increases up to 2 hours. Moreover, the high-temperature operation (1000 °C) of the PLD meant no significant GaN meltback occurred on the GaN template surface. The completed GaN templates were subjected to MOCVD treatment to regrow a GaN layer. The results of X-ray diffraction analysis and photoluminescence measurements show not only the reliability of the GaN template, but also the promise of the PLD technique for the development of GaN-on-Si technology.

Performance of InGaN Light-Emitting Diodes Fabricated on Patterned Sapphire Substrates with Modified Top-Tip Cone Shapes

InGaN light-emitting diodes (LEDs) were fabricated on cone-shaped patterned sapphire substrates (PSSs) by using low-pressure metalorganic chemical vapor deposition. To enhance the crystal quality of the GaN epilayer and the optoelectronic performance of the LED device, the top-tip cone shapes of the PSSs were further modified using wet etching. Through the wet etching treatment, some dry-etched induced damage on the substrate surface formed in the PSS fabrication process can be removed to achieve a high epilayer quality. In comparison to the LEDs prepared on the conventional sapphire substrate (CSS) and cone-shaped PSS without wet etching, the LED grown on the cone-shaped PSS by performing wet etching for 3 min exhibited 55% and 10% improvements in the light output power (at 350 mA), respectively. This implies that the modification of cone-shaped PSSs possesses high potential for LED applications.

Fabrication of nitride LEDs using chemical lift-off from a GaN/sapphire template

Summary form only given. In this study, a nitride light-emitting diode (LED) with an electroplated Cu substrate was detached from a GaN/sapphire (Eco-GaN) template by chemical lift-off (CLO) using an AlN/strip-patterned-SiO2 intermediate sacrificial layer. To etch the patterned SiO2 and AlN layers, the HF and 80°C-KOH solutions were used, respectively. Moreover, a highly lateral etching rate of 0.5 um/hr was obtained as the etching treatment was performed to AlN layer. In comparison to the conventional LED, the vertical-type LED fabricated on the Cu substrate possessed a higher output power of 212 mW, at an injection current of 350 mA. From our evaluation, the output power of LED/Cu substrate had 86% enhancement as compared with that of conventional LED. It reveals the good optoelectronic performance of the LED device on Cu substrate is achieved through the CLO process.

Effect of Top-Region Area of Flat-Top Pyramid Patterned Sapphire Substrate on the Optoelectronic Performance of GaN-Based Light-Emitting Diodes

The flat-top pyramid patterned sapphire substrates (FTP-PSSs) have been prepared for the growth of GaN epilayers and the fabrication of lateral-type light-emitting diodes (LEDs) with an emission wavelength of approximately 470 nm. Three kinds of FTP-PSSs, which were denoted as FTP-PSS-A, FTP-PSS-B, and FTP-PSS-C, respectively, were formed through the sequential wet etching processes. The diameters of circle areas on the top regions of these three FTP-PSSs were 1, 2, and 3 ?m, respectively. Based on the X-ray diffraction results, the full-width at half-maximum values of rocking curves at (002) plane for the GaN epilayers grown on conventional sapphire substrate (CSS), FTP-PSS-A, FTP-PSS-B, and FTP-PSS-C were 412, 238, 346, and 357 arcsec, while these values at (102) plane were 593, 327, 352, and 372 arcsec, respectively. The SpeCLED-Ratro simulation results reveal that the LED prepared on FTP-PSS-A has the highest light extraction efficiency than that of the other devices. At an injection current of 350 mA, the output powers of LEDs fabricated on CSS, FTP-PSS-A, FTP-PSS-B, and FTP-PSS-C were 157, 254, 241, and 233 mW, respectively. The results indicate that both the crystal quality of GaN epilayer and the light extraction of LED can be improved via the use of FTP-PSS, especially for the FTP-PSS-A.

GaN-based LEDs Fabricated on Cone-Shaped Patterned Sapphire Substrates with Modified Top-Tip

GaN-based light emitting diodes (LEDs) structure were grown on the cone-shaped patterned sapphire substrates (PSSs) using metalorganic chemical vapor deposition. To improve the crystal quality of nitride epilayer and optoelectronic performance of LED device, the top-tip cone shapes of PSSs were further modified by wet etching. Using wet etching process, some dry-etched induced damage on substrate surface created during the PSS fabrication process could be removed, resulting in higher crystal quality of epilayer and better device performance. In comparison to the LEDs grown on the conventional sapphire substrate (CSS) and cone-shaped PSS without wet etching, the LED prepared on the cone-shaped PSS with wet etching for 3 minhad 55% and 10% improvement in output power at a driven current of 350 mA, respectively. It reveals that the technique of the modification in PSS shape is potentially useful in LEDs application.

The growth of hexagonal GaN-on-Si(100) using pulsed laser deposition

The growth of hexagonal GaN-on-Si(100) sample prepared by pulsed laser deposition (PLD) was employed in the development of GaN-on-Si technology. In contrast to common GaN-on-sapphire and GaN-on-Si(111) technologies, the use of the GaN film on Si(100) by PLD provides low-cost and large-area single crystalline GaN template for GaN applications, via a single growth process without any interlayer or interruption layer. The evolution of GaN growth mechanism on Si(100) substrate with various growth times is established by SEM and TEM data, which indicated that the growth mode of the GaN films gradually changes from island growth to layer growth when the growth time increases up to 2hrs. Moreover, no significant GaN meltback was found on the GaN sample surface due to the high-temperature operation of PLD. The GaN sample was subjected to MOCVD treatment to regrow a GaN layer. The results of X-ray diffraction analysis and photoluminescence measurement show the reliability of the PLD-GaN sample and are promising for the development of the GaN-on-Si technology using PLD technique.

Modified cone shapes on patterned sapphire substrates for high performance InGaN LED applications

In this study, GaN-based light emitting diodes (LEDs) were prepared on the cone-shaped patterned sapphire substrates (PSSs) by metal-organic chemical vapor deposition. To improve the epilayer quality and device performance of LEDs, the PSSs were further wet etched to form the modified top-tip cone shapes. With increasing the wet etching time to 3 min, the LED grown on the cone-shaped PSS has 53% and 8% enhancement in light output (@ 20 mA) as compared with that on conventional sapphire substrate (CSS) and the cone-shaped PSS without wet etching, respectively.

Study on GaN epilayer transferring to Cu substrate from sapphire substrate using Ga2O3 sacrificial layer

GaN epilayer can be grown on sapphire substrate with a Ga2O3 sacrificial layer. It was employed for the epilayer transferring from sapphire substrate to Cu substrate using the chemical lift-off process application. The (-201) oriented β-Ga2O3 thin film was first deposited on the c-plane sapphire substrate, followed by the GaN growth via metalorganic vapor phase epitaxy under N2 and H2 environment in sequence. The crystal quality of GaN epilayer can be improved dramatically with the regrowth in a H2 ambient. A GaN epilayer with an electroplated copper substrate was demonstrated using a chemical lift-off process where the Ga2O3 sacrificial layer can be laterally etched out with a hydrofluoric solution. It is worthy to mention that the separated sapphire substrate can be cleaned and reused for LED epitaxial growth next time. It is benefiting the cost down for the LED fabrication and Green Photonics Development.

Chemical Lift-Off of Blue Light-Emitting Diodes Grown on Sapphire Substrate with an Oxide-Patterned Sacrificial Layer

III-nitride semiconductors have become attractive materials for the fabrication of optoelectronic and electronic devices. In particular, high-brightness GaNbased light-emitting diodes (LEDs) have become popular for a number of applications. However, the high LEDs performance is still limited in the poor electrical and thermal conductivities of sapphire substrates. To improve this situation, a laser lift-off (LLO) technique was utilized to fabricate vertical GaN LEDs without sapphire. Unfortunately, the LLO technique has some disadvantages such as high cost, complex fabrication and irradiative damage and defects in the GaN layer. Recently, detaching sapphire substrate by chemical lift-off (CLO) processes has been reported, where CrN or ZnO is used as a sacrificial layer so that the LEDs are unaffected by any physical and thermal treatment during CLO process. This suggests that the CLO process may offer another choice for separating sapphire substrate in vertical LED applications.