Growth and optical properties of GaN-based non- and semipolar LEDs

Abstract

The development of smooth (0001) GaN films on c-plane sapphire [1] and the activation of p-dopants in GaN [2] led very quickly to the realization of high brightness InGaN LEDs on c-plane sapphire substrates [3, 4]. Already at the end of the last century blue and green LEDs with tens and hundreds of milli-Watt output power levels were demonstrated. Today, blue InGaN LEDs boast record external quantum efficiencies exceeding 80% and the emission wavelength of c-plane InGaN QW LEDs has been pushed into the yellow and even red spectral range. Although the performance characteristics of c-plane LEDs seem excellent, the strong polarization fields at InGaN/GaN heterointerfaces can lead to a significant deterioration of the device performance. This polarization field is suppressed or reduced in LEDs with InGaN/GaN heterointerfaces of nonpolar or semipolar orientation, respectively. Triggered by the first demonstration of nonpolar GaN quantum wells grown on LiAlO $$:2$$ by Waltereit and colleagues in 2000 [5], impressive advancements in the field of non- and semipolar nitride semiconductors and devices have been achieved. Today, a large variety of heterostructures free of polarization fields exhibiting exceptional optical properties have been demonstrated, and the fundamental understanding of polar, semipolar, and nonpolar nitrides has made significant leaps forward. This chapter is intended to provide an overview on the epitaxial growth and optical properties of group-III-nitride LEDs on non- and semipolar surface orientations [6]. After introducing the physical origins of piezoelectric and spontaneous polarization effects in group-III nitrides, different approaches for the heteroepitaxial growth of low defect density non- and semipolar (Al, In)GaN layers and (Al, In)GaN/GaN heterointerfaces are presented, followed by a discussion of the effect of surface orientation on the indium incorporation efficiency in InGaN layers and quantum wells. In the third section, the polarized light emission characteristics and the optical properties of non- and semipolar InGaN QWs are discussed and finally the performance characteristics of non- and semipolar LEDs are presented including the effects on droop, wavelength shift, and external quantum efficiencies of state-of-the-art devices.