PVT法氮化铝晶体铝面、氮面生长对比分析

在氮气环境下用PVT方法生长氮化铝过程中,氮面和铝面由于表面化学性质不同,生长的主要化学反应速度存在差异。原子在生长表面的迁移能力不同造成单晶表面生长方式差异较大。在基本相同条件下(生长温度、生长温差、生长气压、类似的籽晶、同一台生长设备)进行了铝、氮面氮化铝单晶晶体生长。为了更明显地表现铝氮面的差异,将同一片籽晶分为两半,翻转其中一半让铝氮面同时生长。铝面生长较好的区域形成了明显的晶畴,而氮面生长时生长较好的部分出现了明显的生长台阶,并出现了晶畴边界被生长台阶湮灭的生长现象,进一步通过AFM观测到铝面生长台阶平整但被缺陷所阻隔,晶畴发育明显为各晶畴独立生长。氮面生长台阶没有铝面规则但连续性较强,在原来晶畴边界位置也出现了连续的生长台阶(或台阶簇)。所以籽晶质量不高时氮面生长更容易提高晶体质量,后续的XRD测量结果也证明了氮面生长后的晶体质量明显高于铝面生长的晶体质量。

Growth Comparative Analysis of Aluminum Nitride Crystal by PVT Method on Al Surface and N Surface

For the growth of AlN crystal by PVT method in nitrogen environment, the growth rate is different due to the different surface chemical properties between Al-polar and N-polar. And differentiated growth behaviors were observed within these surfaces due to the disparate migration behaviors of atoms. AlN growth on Al and N surfaces were carried out under the same conditions, i.e., growth temperature, thermal gradients, pressure, seeds and in the same apparatus. With the purpose of evidently exhibiting the discrepancy of Al and N surfaces, an Al-N growth within one growth cycle was realized by turning half of the seed crystal. For the Al-polar growth, domain boundaries merely within the well-grown planes were found. While for the growth on N surface, morphologies with well-aligned steps were observed, and grain boundaries are covered by these steps at the secondary growth.The growth step of Al surface is smooth but obstructed by defects, and the domain development is obviously independent of each domain growth which were further observed by AFM. The growth step of N surface is not regular but more continuous than that of Al surface, and the continuous growth step (or step cluster) also appears at the original boundary of crystal domain. Consisted with the XRD results, it can be figured out that, N growth is an effective approach to obtain an improved crystalline quality for AlN seeds with lower crystallinity.