High Output Power Near-Ultraviolet and Violet Light-Emitting Diodes Fabricated on Patterned Sapphire Substrates Using Metalorganic Vapor Phase Epitaxy(<Special Issue>LED Lighting Technologies)

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Near-Ultraviolet (NUV) and violet light-emitting diodes (LEDs) with an InGaN multi-quantum-well (MQW) structure were fabricated on patterned-sapphire substrate (PSS) using a single growth process of metalorganic vapor phase epitaxy (MOVPE). The PSS with parallel grooves along the <112^^-0>_<GaN> direction or the <11^^-00>_<GaN> direction was fabricated by standard photolithography and subsequent reactive ion etching (RIE). In this study, the PSS with parallel grooves along the <112^^-0>GaN direction was used. The GaN layer grown by lateral epitaxy on a patterned substrate (LEPS) had dislocation density of 1.5×10^8 cm^<-2>. The LEPS-NUV (or violet)-LED chips were mounted on the Si bases in a flip-chip bonding arrangement. When the LEPS-NUV-LED (the emission peak wavelength λ_p: 382 nm) was operated at forward-bias current of 20 mA at room temperature, the output power (P_o) and the external quantum efficiency (η_e) were 15.6 mW and 24%, respectively. When the LEPS-violet-LED (λ_p: 405 nm) was operated at forward-bias current of 20 mA at room temperature, the output power and the external-quantum efficiency were 26.3 mW and 43%, respectively. The PSS is very effective in reducing the dislocation density and increasing the extraction efficiency in the LEDs because of the scattering of the emission light at the patterned GaN/sapphire interface.
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