6Mechanism of Selective Area Growth by MBE
Katsumi Kishino
Department of Engineering and Applied Science, Sophia University, Tokyo, 102‐8554, Japan
6.1 Background
GaN‐based nanocolumns, which are also referred to as nanowires, nanorods, and nanopillars, were first self‐organized on (0001) sapphire substrates by RF plasma‐assisted molecular beam epitaxy (RF‐MBE) [1]. Recently, nanocrystals have attracted considerable attention among researchers, because their properties enable high crystalline quality, such as dislocation‐free nature [2], high light extraction efficiency, and strain relaxation [3]. Using self‐organized nanocolumns on Si, blue to red light‐emitting diodes (LEDs) have been fabricated. However, we have frequently observed near‐field images of nanocolumn LEDs with multicolor emissions, in which micrometer‐scale spots of various colors, including red, green, blue, and yellow (RGBY), were observed in the vicinity of each other [4]. The self‐organization of nanocolumns occurs through random and spontaneous crystal nucleation, which introduces fluctuations in their diameter and position, resulting in the variation of emission color among InGaN‐based nanocolumns. In contrast, the uniform arrays of GaN nanocolumns, which are achieved through precise control in the size and position of nanocolumns [5,6], can resolve the problem.
In this section, the mechanism of selective area growth (SAG) by RF‐MBE of GaN nanocolumns using nanomask patterns is described. By flowing nitrogen gas ...