Formation of m-plane AlN on plasma-nitrided m-plane sapphire

Abstract

Microwave plasma using a gas mixture of N 2 and H 2 has been applied for the nitridation of m-plane sapphire substrate to form a thick epitaxial AlN film. The X-ray diffraction results show that the AlN films formed on the sapphire surface by nitridation for a period from 10-60 min are in (1010) orientation and have an epitaxial relationship with the substrate. The thickness of the nitride film increases with nitridation time and approaches about 0.5 μm after nitridation for 1 h, while the film surface becomes rough. The film quality is reasonably good, as evaluated with the X-ray rocking curve of (1010) AlN. Faceted voids in the sapphire substrate underneath the AlN are also observed with inclined a-plane facets after nitridation.

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

“…In sample B, the buffer layer temperature is kept at 800 • C and the nitridation temperature is increased to 1300 • C. Although the additional diffraction peaks still exist, the (10-13) diffraction peak is narrowed as shown in Figure 1b. In contrast, for sample C, the nitridation temperature is 1050 • C, while the buffer layer temperature rises to 1300 • C. From Figure 1c, it is clearly to see that the intensity of impurity peaks of (10)(11) and (20)(21)(22) is significantly reduced. Comparing with sample A, B and C, we can conclude that high-temperature nitridation and high-temperature buffer layer are promising to improve the crystal quality of the semi-polar (10-13) AlN.…”

“…Low-temperature (1050 • C) nitridation and low-temperature (800 • C) buffer layer are first tried to grow semi-polar (10-13) AlN. In Figure 1a, (10)(11) and (20)(21)(22) diffraction peaks are also observed except the strong (10-13) diffraction peak, indicating that sample A is not the single crystal. In sample B, the buffer layer temperature is kept at 800 • C and the nitridation temperature is increased to 1300 • C. Although the additional diffraction peaks still exist, the (10-13) diffraction peak is narrowed as shown in Figure 1b.…”

“…(800 °C) buffer layer are first tried to grow semi-polar (10-13) AlN. In Figure 1a, (10)(11) and (20)(21)(22) diffraction peaks are also observed except the strong (10-13) diffraction peak, indicating that sample A is not the single crystal. In sample B, the buffer layer temperature is kept at 800 °C and the nitridation temperature is increased to 1300 °C.…”

“…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. In contrast, the (10-13) plane has a positive polarization field, which is favorable for the devices [12].…”

“…According to the epitaxial relationship, it can be determined that the lattice mismatch between m-plane sapphire and (10-13) AlN is the smallest [12]. When growing AlN on sapphire [16][17][18][19], nitridation is a common method to improve crystal quality [20,21]. Moreover, nitridation has a large impact on the crystal orientation of semi-polar AlN [22,23].…”