采用微区拉曼光谱对生长在湿法腐蚀获得的无掩膜周期性图形蓝宝石衬底上GaN材料做了研究,结果显示,侧向外延生长区域具有较低的压应力。采用湿法腐蚀结合原子力显微镜对材料的位错进行了表征,侧向外延区域显示了低的位错密度,具有较高的晶体质量。另外通过对不同生长区域的拉曼纵光学声子与等离子体激元形成的耦合模高频支进行拟合,结果显示侧向外延区域具有较低的背底载流子浓度。研究认为,由于采用图形衬底,侧向外延区域悬空生长降低了位错密度,同时侧向外延区域不与蓝宝石接触,因此采用该方法生长的GaN材料具有较低的压应力和较低的背底载流子浓度。

Micro-Raman spectroscopy is performed to characterize GaN films grown on the patterned sapphire (0001) fabricated by wet chemical etching. The stress distributions are characterized by the frequency shift in the micro-Raman spectroscopy measurements. Residual stress state and carrier concentration in the mesa and wing region are assessed. The wing region shows lower compressive stress and less carrier concentration in comparison with mesa region. That is due to the interactions between sapphires and GaN as the result of diffe-rences in the coefficients of thermal expansion are excluded in the wing region by adopting maskless periodically grooved sapphire,thus less compressive stress and lower background carrier concentration can be achieved by this method.