Abstract
GaN/InGaN based violet light emitting diodes (LEDs), emitting at 430 nm, have been grown on conventional single side polished (SSP) and patterned sapphire substrates (PSS). Characteristics of the epitaxial wafers and subsequently fabricated LEDs have been analyzed. The photoluminescence (PL) peaks have been observed at 428.1 nm 426.1 nm for the epitaxial layers on SSP and PSS respectively. The PL intensity is 2.9 times higher in the case of PSS. The electroluminescence (EL) peaks have been observed at 430.78 nm and 430.35 nm for the LEDs on SSP and PSS respectively. The light output from LED fabricated on the PSS is 2.15 times higher than that of the LED on SSP at a forward current of 100 mA.
Highlights
GaN is one of the most widely used direct band gap compound semiconductors with many optoelectronic applications
We investigated the performance of light emitting diodes (LEDs) grown by metal-organic chemical vapour deposition (MOCVD) on single side polished (SSP) sapphire substrate and patterned sapphire substrate (PSS)
The active region consists of 3 nm thick five quantum wells of InGaN separated by 10 nm thick GaN barriers. 15 nm thick Al0.15Ga0.85N was employed as an electron blocking layer followed by a 120 nm thick p-GaN layer with a carrier concentration of ~5 × 1017 cm−3
Summary
GaN is one of the most widely used direct band gap compound semiconductors with many optoelectronic applications. The main drawback for this material is the presence of a high threading dislocation density (TDD) due to the lattice mismatch between the sapphire substrate and the epitaxial GaN layer. Growth of epitaxial GaN on free-standing GaN substrate would reduce the TDD; the GaN substrates are much costly compared to the sapphire substrates. Another approach to alleviate this problem is the growth of GaN by epitaxial-lateral overgrowth (ELOG) technique, which involves several steps of processing the GaN wafer before the overgrowth. Growth of GaN on patterned sapphire substrate (PSS) is the simplest and most cost effective method to reduce the TDD. There has been a tremendous effort to increase
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