Dept. of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ.
Phys Chem Chem Phys. 2012 Jul 21;14(27):9558-73. doi: 10.1039/c2cp40998d. Epub 2012 Jun 8.
The optimisation of GaN-based electronic and optoelectronic devices requires control over the doping of the material. However, device performance, particular for lateral transport electronic devices, is degraded by the presence of unintentional doping, which for heteroepitaxial GaN layers grown in the polar (0001) orientation is mainly confined to a layer adjacent to the GaN/substrate interface. The use of scanning capacitance microscopy (SCM) has demonstrated that this layer forms due to the high rate of incorporation of gas phase impurities, primarily oxygen, during the early stages of growth, when N-rich semi-polar facets are often present. The presence of such facets leads to additional unintentional doping when defect density reduction strategies involving a three-dimensional growth phase (such as epitaxial lateral overgrowth) are employed. Many semi-polar epitaxial layers, on the other hand, exhibit significant unintentional doping throughout their thickness, except when a three-dimensional growth phase is introduced to aid in defect density reduction resulting in the presence of (0001) and non-polar facets which incorporate less dopant. Non-polar epitaxial samples exhibit behaviour more similar to (0001)-oriented material, but oxygen diffusion from the sapphire substrate along prismatic stacking faults also locally affects the extent of the unintentional doping in this case.
优化基于 GaN 的电子和光电设备需要控制材料的掺杂。然而，设备性能，特别是对于横向传输电子设备，由于存在非故意掺杂而降低，对于在极性（0001）取向外延生长的异质 GaN 层，这种非故意掺杂主要局限于与 GaN/衬底界面相邻的一层。扫描电容显微镜（SCM）的使用表明，由于在生长的早期阶段气相杂质（主要是氧）的高掺入速率，当存在富 N 半极性晶面时，通常会形成这种层。当采用涉及三维生长相（例如外延横向过生长）的减少缺陷密度策略时，这些晶面的存在会导致额外的非故意掺杂。另一方面，许多半极性外延层在其整个厚度上都表现出明显的非故意掺杂，除非引入三维生长相以帮助减少缺陷密度，从而导致（0001）和非极性晶面的存在，这些晶面掺入的掺杂剂较少。非极性外延样品表现出与（0001）取向材料更相似的行为，但氧从蓝宝石衬底沿着棱柱形位错的扩散也会在这种情况下局部影响非故意掺杂的程度。
