Structural properties of sapphire single crystal wafers of 6 inch large-diameter used for LED substrate and AlxGa1-xN thin-films for LED active layers were investigated with high-resolution XRD (HRXRD). Optical properties of AlGaN thin-films were also analyzed with photoluminescence (PL).
Wafer mapping of rocking curve measurements for commercial sapphire wafers grown by Cz(Czochralski), Ky(Kyropoulos), VHGF(vertical horizontal gradient freezing) was carried out, and crrystalline quality in terms of peak FWHMs of rocking curves were compared. Crystalline quality of both VHGF and Ky sapphire wafers were from 4 to 7 arcsec, but that of Cz wafer was from 4 to 20 arcsec, indicating that the quality and the wafer uniformity of VHGF and Ky wafers are better than those of Cz wafer. Using KRISS method, the surface orientation of a sapphire wafer was determined, and the result was compared with the result by the ASTM method. Standard deviation of the result of KRISS method was smaller than the value of the ASTM method. Residual surface damage for 0.85, 1, 1.3 mm thick sapphire wafers of different processing conditions was also measured by a reciprocal space mapping (RSM) technique, and the damage was quantified. Surface damage of 0.85 and 1 mm thick sapphire wafers was approximately 4 arcsec, but the damage of 1.3 mm thick wafer was 23 arcsec, showing that the damage of 1.3 mm thick wafer is much larges than that of 0.85 and 1 mm thick wafers.
AlGaN thin-films were grown on GaN/LT-GaN/sapphire(0001) substrate by metal organic chemical vapor deposition (MOCVD). The growth temperature, pressure, time and TMGa source flow rate were fixed around 1030℃, 100 Torr, 40 min and 120 μmol/min, respectively. TMAl source flow rate were varied from 60 μmol/min to 120 μmol/min. Al compositions of AlGaN thin-films were analyzed with RSM. Al composition increased from 17 to 30 % as TMAl source flow rate increased. As Al composition increased, thicknesses of AlGaN thin-films decreased. Band-gap bowing parameter of the AlGaN active layers was determined by PL and high-resolution XRD results, and the bowing parameter is 1.30±0.02 eV, which is similar to the reported value.