Growth of Semi-Polar (101¯3) AlN Film on M-Plane Sapphire with High-Temperature Nitridation by HVPE

Abstract

Aluminum nitride (AlN) films were grown on the m-plane sapphire by high-temperature hydride vapor phase epitaxy (HVPE). The effect of high-temperature nitridation on the quality of AlN film was studied. The high-temperature nitridation is favorable for the formation of semi-polar single (101¯3) orientation AlN film, the quality of which shows strong dependence on the nitridation temperature. The full width at half maximum of X-ray diffraction for (101¯3) AlN film was only 0.343° at the optimum nitridation temperature of 1300 °C. It is found that the nano-holes were formed on the surface of substrates by the decomposition of sapphire in the process of high-temperature nitridation, which is closely related to the quality improvement of AlN. At the critical nitridation temperature of 1300 °C, the average size of the nano-holes is about 70 nm, which is in favor of promoting the rapid coalescence of AlN micro-grains in the early stages. However, the size of nano-holes will be enlarged with the further increase of nitridation temperature, which begins to play a negative role in the coalescence of AlN grains. As a result, the grain size will be increased and extended to the epilayer, leading to the deterioration of the AlN film.

Effect of High-Temperature Nitridation and Buffer Layer on Semi-Polar (10–13) AlN Grown on Sapphire by HVPE

“…The FWHM values are 0.359 • and 0.356 • for (0002) and (10-13) diffraction, respectively. It is very close to the value of literature [6].…”

“…The FWHM values are 0.359° and 0.356° for (0002) and (10-13) diffraction, respectively. It is very close to the value of literature [6]. Figure 3 shows the cross-sectional SEM images of the four samples.…”

“…Moreover, in sample A, there are many holes as large as 200 nm at the growth interface. In the case of low-temperature nitridation and buffer layer, high density of AlN defects appear and AlN grains are not easy to merge at the initial growth stage [6], resulting in that sapphire can't be completely covered by AlN film. During the high-temperature (1500 • C) growth, due to lack of AlN protective layer, the exposed sapphire surface is decomposed, leading to large holes in sample A as shown in Figure 1a.…”

“…However, the strong spontaneous and piezoelectric polarization along c-axis will weaken the recombination of carriers in the quantum wells [4], which in turn decrease the luminescence efficiency of devices. The use of semi-polar substrates and epitaxial layers [5][6][7][8][9], such as (10)(11), (10)(11)(12) and (10-13) AlN, can effectively solve this problem since the polarization field is greatly weakened [10,11]. According to the energy band structure, other semi-polar plane, such as (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), can produce a negative polarization field across multiple quantum wells used in optoelectronic devices, which can reduce the confinement of hole states and increase the carrier loss.…”

“…Semi-polar nitride films were generally grown on M-plane sapphire [5,6], silicon [7,8] and ZnO [13,14]. It is also reported that native semi-polar AlN substrate were used for homoepitaxial semi-polar AlN [15].…”