In situ Gravimetric Monitoring of Decomposition Rate on Surface of (1012) R-Plane Sapphire for High-Temperature Growth of Nonpolar AlN

Abstract

The thermal stability and reaction with H 2 of the surface of a (10 1 12) R-plane sapphire substrate at high temperatures were investigated using an in situ gravimetric monitoring system. Although the R-plane sapphire surface was stable up to 1400 C in an inert carrier gas, decomposition started at 1200 C in H 2 carrier gas. In addition, the activation energy for the decomposition of R-plane sapphire in H 2 carrier gas changed at approximately 1300 C, which indicates that the rate-limiting reaction for the decomposition of the R-plane sapphire substrate shifts near 1300 C. These results agree with those for the stability of the C-plane sapphire substrate, as described previously. However, it was found that decomposition rate of the R-plane sapphire substrate was significantly greater than that for the C-plane substrate. The relationship between the decomposition rate and the surface orientation of sapphire and detailed mechanisms for the decomposition of R-and C-plane sapphire in H 2 carrier gas are discussed.

In situ gravimetric monitoring of surface reactions between sapphire and NH3

“…1 shows a comparison of the decomposition rates in a flowing He [7], 0.1 atm NH 3 +He, and 0.1 atm H 2 +He. In a flowing He, the decomposition of sapphire was not observed below 1400 1C; however, a low rate of decomposition was observed above 1400 1C, which may be due to the direct desorption of Al, O 2 , and AlO x from the sapphire surface [7,8]. In the 0.1 atm NH 3 +He flow, decomposition and/or reaction started to occur from 1300 1C, indicating that NH 3 significantly facilitates the surface reaction of C-plane sapphire.…”

“…Recently, high-quality AlN was fabricated over 1400 1C on a C-plane sapphire substrate [4][5][6]; however, little is known about the stability of C-plane sapphire substrates at such high temperatures. In our previous study, the thermal stability of sapphire and the reaction mechanisms between a sapphire surface and H 2 at high temperatures above 1200 1C were investigated using the in situ gravimetric monitoring (GM) system [7,8]. It was clarified that the sapphire surface is stable up to 1400 1C in flowing He at atmospheric pressure, and decomposition of the surface occurs at 1200 1C in flowing H 2 .…”

“…In this study, the reaction mechanisms between sapphire surface and NH 3 at high temperatures above 1200 1C were investigated using the in situ GM system [7,8]. This system is a powerful tool for investigating the surface reaction mechanisms, because it provides direct information on the decomposition rate due to the surface reaction in real time with a monolayer level.…”

Investigation of void formation beneath thin AlN layers by decomposition of sapphire substrates for self-separation of thick AlN layers grown by HVPE

“…To develop a method for the in situ self-separation of thick AlN layers from sapphire substrates at high temperatures, we made detailed investigations into the stability of both AlN [25] and sapphire [26] in various gas flows, and found that both AlN and sapphire decompose by reaction with the H 2 contained in the carrier gas at temperatures above 1200 1C, with the order of decomposition rate (0 0 0 1)AlNo(0 0 0 1) sapphire o(1 0 1 2) sapphire. Furthermore, decomposition of AlN was found to be suppressed by the addition of NH 3 to the gas flow containing H 2 .…”

Controlled formation of voids at the AlN/sapphire interface by sapphire decomposition for self‐separation of the AlN layer

“…Input partial pressures of AlCl 3 and NH 3 were 5.0 × 10 -4 and 1.3 × 10 -3 atm, respectively. Then, heat treatment was performed at 1450 ºC for 0 to 60 min in a carrier gas (H 2 + N 2 ) containing NH 3 to suppress decomposition of the thin AlN layer [15] and to decompose the sapphire beneath the AlN layer by reacting it with hydrogen [16,17]. After that, the thick AlN layer growth was performed at 1450 ºC for 4 h on the thin AlN layers with an increased NH 3 input partial pressure of 2.0 × 10 -3 atm.…”