In situ gravimetric monitoring of decomposition rate on the surface of (0001) c‐plane sapphire for the high temperature growth of AlN

Abstract

The thermal stability of (0001) sapphire was investigated at atmospheric pressure using the in situ gravimetric monitoring (GM) method. The weight change of a sapphire substrate was monitored at various hydrogen partial pressures in carrier gas (PH2) at temperatures over 1200 °C. Although the sapphire substrate was stable up to 1450 °C in an inert carrier gas (PH2 = 0.0 atm), sapphire decomposition started to occur at 1200 °C in H 2 carrier gas (PH2 = 1.0 atm). Moreover the activation energy and order of reaction for sapphire surface decomposition changed at approximately 1300 °C. These results indicate that the rate-limiting reaction for sapphire decomposition shifts near 1300 °C. 1 Introduction Group-III nitrides such as InN, GaN and AlN are very promising materials for potential use in optical devices and high-speed electronic devices. These materials and their alloys, such as InGaN and AlGaN, have a direct-transition band structure and cover the energy band gap range from 0.7 to 6.2 eV, which corresponds to the emission wavelength range from 200 nm (UV) to 1770 nm (IR). In particular, since AlN has the widest band gap energy (6.2 eV) and high thermal conductivity (3.3 W m

High-temperature growth of thick AlN layers on sapphire (0 0 0 1) substrates by solid source halide vapor-phase epitaxy

“…Conversely, the concentration of oxygen near the interface between AlN and sapphire is much higher (mid-10 19 cm À3 ) than that at the surface. According to the previous work, decomposition of c-plane sapphire starts to occur at 1450 1C in the inert carrier gas [18]. Therefore, we can conclude that the origin of highly incorporated oxygen in the AlN layer is caused by the diffusion of oxygen from the decomposed sapphire substrate at such a high temperature.…”

“…This is thought to be due to the decomposition of AlN and/or sapphire starting substrate. Actually, Akiyama et al [18] reported using gravimetric monitoring system that the thermal decomposition of c-plane sapphire started to occur at over 1200 and 1450 1C in the H 2 ambient and He (inert gas) ambient, respectively. Also, in the H 2 ambient, thermal decomposition of AlN started to occur at around 1400 1C [19].…”

Effects of AlN nucleation layers on the growth of AlN films using high temperature hydride vapor phase epitaxy

“…Several techniques for growing aluminum nitride layers on a variety of substrates have AlN deposition requires a high growth temperature above 1200 • C [14,17]. Nevertheless, thermal decomposition of c-plane sapphire starts to occur at 1200 • C [18] and AlN starts to decompose around 1400 • C [19] by reacting with hydrogen (H 2 ) used as a carrier gas, resulting in the formation of surface pits and in the degradation of AlN layer quality [20].…”

Growth of thin protective AlN layers on sapphire substrates at 1065 °C for hydride vapor phase epitaxy of AlN above 1300 °C

“…More recently, we have reported high-temperature growth of AlN on sapphire above 1300 ºC using a hybrid HVPE system having a resistance heating susceptor [11,12]. At such high temperatures, however, decomposition of the sapphire substrate occurs with the presence of H 2 [13]. Thus, it is essential to investigate a method for the protection of the sapphire substrate in order to grow AlN at high temperatures.…”

“…These droplets were found to be Al metal and/or alumina whose Al composition is higher than stoichiometry because they were dissolved in an aqueous hydrochloric acid solution. Recently, Akiyama et al investigated the decomposition of sapphire substrates in flowing H 2 [13]. The formation of Al droplets on the sapphire surface before AlN growth may influence AlN growth when AlN is grown directly on the sapphire substrate at high temperatures above 1300 ºC.…”