MOCVD生长的未掺杂GaN的结晶特性与补偿度关系的研究

Relationship Between Structural Characteristics and Compensation Ratio in Unintentionally Doped GaN Grown by MOCVD

对本实验室用 MOCVD方法生长的未故意掺杂的 Ga N单晶膜进行了结晶性能、电学性能研究。结果表明 ,室温时 Ga N的 X射线双晶衍射半高宽与其补偿度有较强的依赖关系。高补偿的 Ga N的 X射线双晶衍射半高宽较宽 ,低补偿的 Ga N的 X射线双晶衍射半高宽较窄。

The correlation of the crystalline quality with the electrical characteristics of the unintentionally doped GaN films has been studied. The growth of unintentionally doped GaN films was performed by MOCVD method using a home made vertical reactor operating at atmospheric pressure. The growth was carried out on (0001) oriented sapphire substrates using trimethylgallium (TMGa) and blue ammonia (NH 3) as Ga and N sources, respectively. The mixed gases of hydrogen and nitrogen were used as the carrier gases. A thin buffer layer with thickness of about 15nm was grown at 520℃ and recrystallized at 1060℃ for 6 minutes. The GaN films were grown at 1060℃. The crystalline quality was analyzed by the Full width at half maximum (FWHM) of double crystal X ray diffraction (DXRD). The electrical properties were measured by Van der Pauw Hall method at the room temperature. Table 1 shows the FWHM of X ray double crystal diffraction and the electrical parameters for GaN films grown by MOCVD on sapphire (0001). Fig.1 shows the function of the electron drift (solid curves) and Hall (dashed curves) mobility on the compensation ratios of 0.00, 0.15, 0.30, 0.45, 0.60, 0.75 and 0.90 for 300K. Fig.2 shows the double crystal X ray rocking curve for unintentionally doped GaN grown by MOCVD on sapphire (0001). These results indicate that there is no obvious relationship between the mobility and the carrier concentration, and neither between the FWHM and the mobility or the carrier concentration. However, there exist an obvious correlation of the FWHM of double crystal X ray diffraction to the compensation ratio at room temperature for the unintentionally doped GaN/Al 2O 3 films. Fig.3 shows the dependence of FWHM on the compensation ratio in unintentionally doped GaN. The FWHM of heavily compensated GaN is broad while that of lightly compensated GaN is narrow. The FWHM becomes wider from 5.6 to 17 minutes with the increasing of the compensation ratios from 0.46 to 0.79. Some possible mechanisms responsible for those phenomena have been analyzed. As for unintentionally doped GaN films with high compensation ratio, the existence of many acceptors and donors will result in deformation in the crystal lattice, so the FWHMs of these samples will be broad. For the samples with low compensation ratio, the lattice deformation is relatively small, and the FWHM is also relatively narrow.