Topological Analysis of Defects in Epitaxial Nitride Films and Interfaces

Abstract

The present work is a review of the topological theory of defects and interfaces in crystalline materials, aimed at illustrating cases that have been studied under this framework in nitride films and interfaces. The review adresses crystallographic calculations in hexagonal and trigonal crystals using the Frank system. It also presents the principal methods of a priori and a posteriori defect characterization in a unified manner, showing their equivalence, the circumstances under which they are applicable, and practical aspects of their deployment. A number of experimental observations are analysed, and useful conclusions are extracted, for example, concerning admissible defects, structure-mechanism relations, and the influence of defects on properties. These include (i) threading, stacking-fault and interfacial dislocations in GaN epilayers, (ii) the influence of the epitaxial interface on the systematic appearance of inversion and stacking disorder, (iii) structural transformations of inversion domain boundaries due to their intersections with stacking faults, and (iv) double-positioning twinning in TiN contact layers deposited on GaN.

Anisotropic strain relaxation and abnormal zigzag shape planar defects in nonpolar a-GaN grown by metalorganic chemical vapor deposition

“…This corresponds to a pure edge dislocation with a low angle boundary. Typically, it is modeled such that pure edge dislocations are formed with different core configurations of 4, 8, and 5/7 atom cycles, which may induce a misorientation of a few degrees [23][24][25]. According to the model of atom cycles, the 5/7 model agrees well with our HRTEM image result, as shown in Fig.…”

Transmission electron microscopy study of a defected zone in GaN on a SiC substrate grown by hydride vapor phase epitaxy

“…The majority of defects found within the GaN layer are threading dislocations ͑TDs͒ that originate near the GaN/substrate interface and extend to the outer surface of the GaN layer. [7][8][9][10][11][12] The threading dislocations tend to be aligned in the growth direction, and their density is usually about 10 10 cm Ϫ2 . The majority of dislocations are reportedly of a type ͑edge dislocations with bϭ1/3͗1120͘); however, both c-type ͑screw dislocations with bϭ1/2͓0001͔) and mixed a ϩc dislocations are also typically observed.…”

“…7 The density of TDs can be significantly reduced by using epitaxial lateral overgrowth ͑ELOG͒ methods. 2 Other defects often present in GaN layers include inversion domain boundaries ͑IDBs͒ which separate domains of opposite polarity, (0001) stacking fault boundaries that result from mismatch of stacks of closepacked layers in hexagonal wurtzite GaN, [7][8][9][10][11][12][13] and planar ͕1120͖ defects a called double positioning boundaries ͑DPBs͒ or stacking mismatch boundaries ͑SMBs͒. 2,7,14,15 In good quality GaN layers, planar defects in IDBs and SMBs are absent at the top of the layers.…”

Anodic Etching of n-GaN Epilayer into Porous GaN and Its Photoelectrochemical Properties

“…A heteroepitaxial GaN film contains various structural defects at the surface like vacancies, dislocations, and pits. 29,30 These defects, particularly threading dislocations, are influenced by the local strain and layer coalescence during epitaxial growth 31 , and therefore distribute non-uniformly. The AlGaN intermediate layers used in our stack is known to reduce the threading dislocation density at the GaN surface to the range of 1-3×10 9 cm -2 .…”

“…37 GaN grown by heteroepitaxy is well known for the rich intrinsic defects at the surface. 29,30 Some of these intrinsic surface defects may facilitate carrier recombination efficiently. During anodic etching, these intrinsic surface defect sites can be preferentially etched due to weak atomic bonding and high chemical activity.…”