Growth and Optical Properties of GaN-Based Non- and Semipolar LEDs

Light emitting diodes (LEDs) based on the (In, Al, Ga) N material system offer the possibility to generate light in the entire visible wavelength range, extending into the ultraviolet and the infrared regions. The widely tunable bandgap makes nitride based LEDs suitable devices for applications such as general energy efficient lighting, water purification, UV curing and medical applications. Conventionally, all group III-nitride based devices have been grown epitaxially on the polar (0001) c-plane of the wurtzite crystal structure. This leads to the formation of strong polarization fields pointing along the [0001] c-axis. These fields reduce the device efficiency through the quantum confined Stark effect (QCSE) and also cause other detrimental effects like wavelength-shifts and efficiency droop with increasing current densities. By growing InAlGaN heterostructures on non-and semipolar growth planes, these fields can be significantly reduced or even eliminated. In addition, due to the reduction of in-plane symmetry, a number of new heterostructure design options emerge to control the optoelectronic properties of non-and semipolar light emitters. Among these are the occurrence of anisotropic strain with the consequence of an anisotropic valence band structure and the possibility to generate strongly polarized light emission from LEDs. In this chapter we will discuss the origin of the polarization fields in III-nitrides and their control by growth on non-and semipolar crystal planes. Different approaches for the homo-and heteroepitaxial growth of non-and semipolar nitride heterostructures as well as structural properties, such as surface morphologies and indium incorporation efficiencies will be discussed. The influence of the crystal plane and the indium content on the valence band structure and the polarization state of the emitted light will be presented and the state-of-theart device characteristics of non- and semipolar LEDs will be reviewed.