Effects of N+-implanted sapphire (0001) substrate on GaN epilayer

Ab initio-based approach to elemental nitridation process of α-Al2O3

“…It can be clearly seen that the adsorption of N atoms occur only below 240 K. This reflects that the adsorption energy for the N adatoms ( À 0.55 eV) is very high. Thus, N atoms cannot adsorb at all on the surface at experimental temperature range [1][2][3][4][5][6][7][8][9]. This result suggests that the nitridation process cannot only be interpreted by N itself but another contribution should also be taken into account.…”

“…We thus take account of the surfaces in which O atoms in the second layer are replaced by N atoms. Based on the experimental results which show the formation of AlN layer [1][2][3][4][5][6][7][8], we also consider the desorption of O atoms in the second layer. and N atoms, so that AlN layer is formed by the desorption of O atoms.…”

“…The nitridation is intuitively understood by structural and chemical changes caused by nitrogen on a-Al 2 O 3 surfaces. Several experimental studies have reported that AlN layers are formed on a a-Al 2 O 3 (0001) surface by exposing ammonia (NH 3 ) [1,2], N-radical [3] or N 2 -plasma [4,5] in molecular beam epitaxy as well as in metal-organic vapor phase epitaxy (MOVPE) [6,7] and hydride vapor phase epitaxy [8]. In contrast to these findings, Uchida et al have found that amorphous AlN x O 1 À x layer is formed on a a-Al 2 O 3 (0001) surface by heating at 1050 1C in NH 3 ambient conditions in the MOVPE [9].…”

The effects of strained sapphire (0001) substrate on the structural quality of GaN epilayer

“…However, it is difficult to obtain high-quality GaN on a sapphire substrate with an atomically flat growth surface and low density of threading dislocations because of differences in lattice constant and thermal expansion coefficient between the sapphire substrate and the GaN epilayer. Hence, many researchers have reported the surface pretreatment of sapphire, which is known to play a critical role in determining the crystal quality of the overgrown GaN epilayer by metal-organic chemical vapor deposition (MOCVD) [6][7][8][9][10][11].…”

Effects of patterned ion implanted sapphire substrate for LED

“…Recently, the N + -ion-implantation process applied directly to the sapphire substrate was reported to be effective as a pretreatment technique in order to grow high-quality GaN [5]. The ex-situ N + -ion implantation process can provide a convenient and reliable method of forming a quasibuffer layer made of materials such as disordered AlN or AlON, which are stable and easy to handle in the process of GaN epilayer growth [6]. Moreover, the GaN grown by the epitaxial lateral overgrowth method on patterned sapphire substrates were successfully used to grow GaN LEDs [7,8].…”