ABSTRACT
III-nitride compounds, especially gallium nitride (GaN), are prom-ising direct band-gap semiconductor materials for optoelectronic applications. In principle, it is easy to tune the emission wavelength of the III-nitride system: add indium to shift emission toward longer wavelength, or add aluminum to move into the UV region. Thus, one can fabricate III-nitride light emitting devices that cover the entire visible and (near-) UV spectrum [1,2].From the fabrication point of view, the substrate used for III-nitride growth is still one bottleneck for developing III-nitride optical devices. Sapphire and SiC are the most common substrates of choice due to the fact that bulk lattice-matched substrates are not readily available. However, both sapphire and SiC are difficult to manufacture. The laser lift-off from sapphire substrates is hardly suitable for mass production. SiC substrates are too expensive for low-cost applications. In recent years, a high-quality III-nitride-
on-silicon system has been developed by using an intermediate AlGaN/AlN buffer layer to reduce the crack density [3-6]. Silicon micromachining is a mature technique for removing the silicon substrate to generate freestanding III-nitride slabs. It is thus feasible to fabricate optical components on thin freestanding III-nitride slabs.The design, fabrication and characterization of III-nitride nanostructures are demonstrated in this chapter. The overall objective is to study the light matter interaction in III-nitride nanostructures. Fundamental studies as well as applied research are carried out with the aim of ultimately offering small, easy-tomanufacture, and efficient III-nitride nanostructures. The strong light-matter interaction is thus investigated in III-nitride nano-structures, and the subsequent realization of III-nitride photonic devices are developed for practical use.This chapter is divided into two parts. Part 1 is focused on III-nitride resonant structures, and is organized as: freestanding III-nitride resonant gratings [7,8], III-nitride resonant structures fabricated by a front-side process [9], and III-nitride resonant structures grown on freestanding HfO2 structures [10]. Part 2 describes the light extraction efficiency improved by III-nitride nanostructures, and includes freestanding circular III-nitride gratings [11], freestanding III-nitride subwavelength nanostructures [12], patterned growth of InGaN/GaN multiple quantum wells (MQWs) [13,14], and freestanding III-nitride nanocolumn slab with bottom subwavelength nanostructures [15,16].
