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Gate length of 1-μm enhancement-mode n-channel GaN MOSFET with MgO and hybrid MgO-TiO 2 stacked gate dielectrics were characterized. The leakage current of a stacked MgO and hybrid MgO-TiO 2 MOS capacitor can be as low as 6.2 × 10 −9 and 6.9 × 10 −9 A/cm 2 at ±1-V bias, respectively. Through a self-aligned process, superior I D -V D and I D -V G electrical characteristics of a MOSFET were obtained. The maximum drain current is 3.69 × 10 −5 A/μm at a gate voltage V g of 8 V and a drain voltage V D of 10 V. The subthreshold swing is 342 mV/dec, and the I ON /I OFF is 5.7 × 10 4 .

In this study, the epilayers of gallium nitride light-emitting diode grown by metallorganic chemical vapor deposition on the stripe-patterned sapphire substrate prepared by chemical wet etching were characterized. The stripe pattern on vertical GaN/Si surface transferred by wafer bonding and laser lift-off techniques from the patterned sapphire substrate contributes much stronger photoluminescence intensity.Gallium nitride ͑GaN͒ blue light-emitting diodes ͑LEDs͒ have been commercially available and widely used as the light sources for backlighting, traffic signals, outdoor displays, and head lamps of automobiles. It is well known that GaN grown on sapphire has high dislocation density due to 16% lattice mismatch, which will degrade GaN characteristics, such as electron mobility, optical quantum efficiency, and carrier and device lifetimes. Therefore, the reduction of dislocation density is an important issue for the improvement of GaN optical and electrical qualities. Many approaches were proposed to reduce the dislocation density of GaN. 1,2 The lateral epitaxial overgrowth with SiN x or SiO 2 stripe-type mask is a common technique and can decrease the dislocation density to the range of 10 7 cm −2 . 3,4 Meanwhile, the GaN epitaxial layer grown directly on the stripe-patterned sapphire substrate ͑GaN/PSS͒ along ͑11-20͒ 5 or ͑1-100͒ directions 6 can have lower dislocation density. By this technique, the contamination from the mask can be prevented and the epilayer growth process is simplified.The poor power dissipation of GaN/sapphire LEDs due to the poor thermal conductivity of sapphire substrate leads to higher junction temperature and degrades its performance. By using wafer bonding and laser liftoff ͑LLO͒ techniques ͑LLO GaN/Si͒, the GaN/sapphire LED can be transformed into a vertical-type GaN/silicon LED. This structure can provide higher performance due to higher thermal and electrical conductivities of silicon substrate. In addition, the larger light-emitting area of the vertical GaN/Si LED can increase the optical output power. [7][8][9] Meanwhile, the texture surface was used on GaAs LEDs to improve the light extraction efficiency. 10 The texture structure was also used on p-GaN 11,12 or n-GaN surfaces 13 of GaN/sapphire LED to improve the light extraction efficiency. However, an additional etching process is needed to form the texture structure and the reproducibility is also an issue. In this study, the stripe-patterned PSS substrate was prepared by chemical wet etching. The LLO technique was used to transform GaN/sapphire into a vertical-type GaN/Si ͑LLO-PSS GaN/Si͒. The stripe-patterned texture structure was obtained simultaneously. Higher optical quality from the stripepatterned texture structure on the surface of LLO-PSS GaN/Si was expected. ExperimentalThe GaN epilayers of a simple LED structure were used in this experiment. Figure 1 shows the fabrication of the GaN/Si structure prepared by sapphire chemical wet etching, GaN epilayer growth, wafer bonding, and LLO techniques. A 2 in., 430 m thick ...

A patterned sapphire substrate with shallow U-shaped stripe grooves along the ͗112 ¯0͘ direction prepared by chemical wet etching was used for the growth of high-quality gallium-nitride-based epilayers without air gap formation. From characterization by scanning electron microscopy, transmission electron microscopy, and micro-photoluminescence, it was determined that the crystalline and optical qualities of gallium-nitride-based epilayers grown on the groove region are better than those on the ridge region. In addition, the qualities of epilayers near the edge area are better than those near the center area on the groove region examined by cathodoluminescence. The growth evolution deduced from the orientations of threading dislocations on the ridge and groove regions was proposed.

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