Abstract
A correlation study between the observed surface morphology using high-resolution scanning electron microscopy (HRSEM) and the observed structural imperfections using transmission electron microscopy (TEM) has been conducted for a-plane GaN. There are three different sized asymmetric surface pits: large pit of 500 nm–2 µm in side length, medium pit of 50 nm in side length, and small pit with side lengths of less than 5 nm, which originate from incomplete island coalescence, screw dislocation, and partial dislocation (PD), respectively. Both screw dislocation and PD can produce pits on the free surface because they have a perpendicular line tension to the surface, which must remain in balance with the surface tension. The two types of dislocation lead to distinctive pit sizes because the PD has a smaller Burgers vector component along the dislocation line than the pure screw dislocation. A pit that is produced in the island-coalescing process is much larger than those caused by dislocations because island coalescence is a kinetic process that involves large-scale mass transportation, whereas the dislocation mediates the surface in the local area. These three types of surface pits sometimes interact with one another in space. The coalescence of the island determines the surface morphology at large scales, whereas the defects affect the details.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Zhang B J, Liu Y. A review of GaN-based optoelectronic devices on silicon substrate. Chin Sci Bull, 2014, 59: 1251–1275
Zhang G Y, Shen B, Chen Z Z. GaN-based substrates and optoelectronic materials and devices. Chin Sci Bull, 2014, 59: 1201–1218
Li F H, Gao X, Yuan Y L, et al. GaN PIN betavoltaic nuclear batteries. Sci China Tech Sci, 2014, 57: 25–28
Huang Y, Li P X, Yang Z, et al. High efficiency and enhanced ESD properties of UV LEDs by inserting p-GaN/p-AlGaN superlattice. Sci China-Phys Mech Astron, 2014, 57: 887–891
Pan Z L, Chen L, Zhang G Z, et al. A single-photon fault-detection method for nanocircuits that use GaN material. Sci China Tech Sci, 2014, 57: 270–277
Pimputkar S, Kawabata S, Speck J S, et al. Photoluminescence evolution in GaAs/AlGaAs core/shell nanowires grown by MOCVD: Effects of core growth temperature and substrate orientation. J Cryst Growth, 2013, 368: 67–71
Fang H N, Zhang R, Liu B, et al. Temperature dependence of the point defect properties of GaN thin films studied by terahertz timedomain spectroscopy. Sci China-Phys Mech Astron, 2013, 56: 2059–2064
Nakamura S. The roles of structural imperfections in InGaN-Based blue light emitting diodes and laser diodes. Science, 1998, 281: 956–961
Wang E P, Bian J M, Qin F W, et al. Effect of TMGa flux on GaN films deposited on Ti coated on glass substrates at low temperature. Chin Sci Bull, 2013, 58: 3617–3623
Xu S R, Lin Z X, Xue X Y, et al. Comparative study of the characteristics of the basal plane stacking faults of nonpolar a-plane and semipolar (11-22) GaN. Chin Phys Lett, 2012, 29: 017803
Xu S R, Hao Y, Zhang J C, et al. Stress and morphology of a nonpolar a-plane GaN layer on r-plane sapphire substrate. Chin Phys B, 2011, 20: 107802
Zhang J, Tian W, Wu F, et al. The effects of substrate nitridation on the growth of nonpolar a-plane GaN on r-plane sapphire by metalorganic chemical vapor deposition. Appl Surf Sci, 2014, 307: 525–532
Song K M, Kim J M, Lee D H, et al. Growth behavior and growth rate dependency in LEDs performance for Mg-doped a-plane GaN. J Cryst Growth, 2011, 326: 135–139
Johnston C F, Kappers M J, Humphreys C J. Microstructural evolution of nonpolar (11-20) GaN grown on (1-102) sapphire using a 3D-2D method. J Appl Phys, 2009, 105: 073102
Hollander J L, Kappers M J, McAleese C, et al. Improvements in a-plane GaN crystal quality by a two-step growth process. Appl Phys Lett, 2008, 92: 101104
Ni X, Fu Y, Moon Y T, et al. Optimization of a-plane GaN growth by MOCVD on r-plane sapphire. J Cryst Growth, 2006, 290: 166–170
Kappers M J, Badcock T J, Hao R, et al. On the origin of blue-green emission from heteroepitaxial nonpolar a-plane InGaN quantum wells. Phys Status Solidi C, 2012, 9: 465–468
Moram M A, Johnston C F, Kappers M J, et al. Measuring dislocation densities in nonpolar a-plane GaN films using atomic force microscopy. J Phys D Appl Phys, 2010, 43: 055303
Kong B H, Sun Q, Han J, et al. Classification of stacking faults and dislocations observed in nonpolar a-plane GaN epilayers using transmission electron microscopy. Appl Surf Sci, 2012, 258: 2522–2528
Hao R, Kappers M J, Moram M A, et al. Defect reduction processes in heteroepitaxial non-polar a-plane GaN films. J Cryst Growth, 2011, 337: 81–86
Sun Q, Yerino C D, Leung B, et al. Understanding and controlling heteroepitaxy with the kinetic Wulff plot: A case study with GaN. J Appl Phys, 2011, 110: 053517
Du D, Srolovitz D J, Coltrin M E, et al. systematic prediction of kinetically limited crystal growth morphologies. Phys Rev Lett, 2005, 95: 155503
Sun Q, Yerino C D, Ko T S, et al. Understanding nonpolar GaN growth through kinetic Wulff plots. J Appl Phys, 2008, 104: 093523
Frank F C. Capillary equilibria of dislocated crystals. Acta Crystallogr, 1951, 4: 497–501
Heying B, Tarsa E J, Elsass C R, et al. Dislocation mediated surface morphology of GaN. J Appl Phys, 1999, 85: 6470–6474
Du D X, Srolovitz D J. Faceted dislocation surface pits. Acta Mater, 2004, 52: 3365–3370
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Gao, Z., Li, J., Xue, X. et al. Different structural origins for different sized surface pits observed on a-plane GaN film. Sci. China Technol. Sci. 59, 156–161 (2016). https://doi.org/10.1007/s11431-015-5959-0
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11431-015-5959-0