AlN is promising among the III-nitride semiconductor for the buffer layer and the UV emitting diode as the template substrate due to its lattice constants close to that of GaN and 6.2eV large bandgap energy. AlN also has the high applicability with the high thermal conductivity and chemical stability for the power electronic device. In particular, the thick AlN epilayers can be used to grow the homo epitaxy layer as the free-standing substrate. For growing the thick AlN epilayer, it is essential to find the growth method with high growth rate like HVPE.
In this study, AlN epilayers were grown on the 2inch sapphire substrate using the horizontal HVPE. The temperature of the source zone and the growth zone of HVPE were set at 950℃ and 1145℃, respectively. The carrier gas was N2 and the growth time was 60min. The gaseous metal chlorides, which is reaction of metallic aluminum with HCl gas was used for III group source and V group source was NH3 gas. N2 gas was flowed for a stable growth atmosphere. The source boat was graphite in order to use the RF induction heating method.
The surface and cross-section images of AlN epilayers on sapphire substrate were observed by SEM. To analysis the components of AlN epilayers, we used EDS, which is attached to SEM. AFM was employed to observe the surface morphology of AlN epilayers. The RMS roughness was 294nm. The structural characteristics of AlN epilayers were studied by XRD using the FWHM and 2theta peak. The FWHM values of (002) and (102) were 0.27° and 1.16°, respectively. The lattice constants can be calculated with Bragg's formula and XRD results. We compared the calculated lattice constants and FTIR measurement. From these results, it was found that there is a strain in AlN epilayers.
Based on the study with the proper growth condition and V/III ratio, it is important to find the solutions for the high-quality AlN epilayers using HVPE. As a result we should improve the potential that HVPE with high growth rate can become a new AlN crystal growth method because the high-quality epilayers affect the performance and lifetime of device.