Structural properties of GaN(0001) epitaxial layers revealed by high resolution X-ray diffraction

Abstract

High-resolution X-ray diffraction has been used to analyze GaN(0001) epitaxial layers on sapphire substrates. Several structural properties of GaN, including the lattice constants, strains, and dislocation densities are revealed by the technique of X-ray dffraction (XRD). Lattice constants calculated from the omega/2theta scan are c=0.5185 nm and a=0.3157 nm. Also, the in-plane strain is −1.003%, while out of the plane, the epitaxial film is almost relaxed. Several methods are used to deduce the mosaicity and dislocation density of GaN, showing that the edge type dislocations are the overwhelming majority. GaN, XRD, dislocation, epitaxialGaN has been widely studied for years because of its wide band gap as well as efficient light emitting properties, which makes it suitable for optoelectronic devices [1, 2]. However, due to the large mismatch with substrates such as SiC, Si, and sapphire, strains and stresses are inevitable in group III-nitride thin films, and a proper treatment of strains and stresses in films is significant for understanding the modification of the band gap. Additionally, intense strains and stresses in GaN thin films lead to high densities of threading dislocations [3] (TDs), which can exceed values of 10 10 cm −2 . In this case, the high magnitude of dislocations would affect the electrical and optical properties of thin films, such as carriers' mobility [4], conductivity [5], and emitting efficiency [1, 6]. Consequently, strains and dislocations in thin films are usually researched with great enthusiasm.These sorts of epitaxial layers can be described by a mosaic model [7], as shown in Figure 1. The epitaxial layer is assumed to consist of many single crystallites, namely mosaic blocks, and their twist rotation (in-plane rotation) as well as tilt rotation (out of plane rotation) which would result in the edge-type dislocations and screw-type dislocations in the thin film, respectively. The vertical and lateral dimensions of the block are represented respectively by certain mean vertical (L // ) and lateral correlation lengths ( L ⊥ ). For wurtzite III-nitrides, screw-type dislocations with a Burgers vector b=[0001] result in a tilt of the lattice planes, which in turn are appearent in the full-width at halfmaximum (FWHM) of symmetric X-ray omega scans (rocking curves). More accurately, the Williamson-Hall plots of the FWHMs of the omega scans with increasing order are needed [ 8]. In addition, the tilt and lateral correlation length can be deduced from the slope and y intercept of these plots. Meanwhile, the tilt and lateral correlation of the mosaic blocks contributing to the broadening of the reciprocal lattice point (RLP) can also be determined from the reciprocal space map in asymmetric diffraction geometry [9].In fact, the dislocation density can be directly measured

Structural characterization of Al 0.55 Ga 0.45 N epitaxial layer determined by high resolution x-ray diffraction and transmission electron microscopy

“…[11] In addition, a mosaic twist can be extracted from rocking curves of asymmetric reflections in off-axis skew symmetric geometries with increasing lattice plane inclination. [14,15] Recently, some literature discussed the above mosaic model and estimated the structural quality of IIInitrides, [16][17][18][19][20][21][22][23][24] which proved the validity of this method.…”

Self-Powered Solar-Blind Photodetectors Based on Vertically Aligned GaN@Ga2O3 Core–Shell Nanowire Arrays

“…Initially, the GaN NAs on the GaN/sapphire templates were prepared by a fabrication process using Ni self-assembled nanomasks, which have been reported in detail elsewhere . The template was undoped GaN layers grown on c-plane sapphire using metal–organic chemical vapor deposition (MOCVD) . After the remaining mask layer was removed, a 300 nm thick SiO 2 layer was deposited on the GaN layer using e-beam evaporation by a shadow mask.…”

“…35 The template was undoped GaN layers grown on c-plane sapphire using metal−organic chemical vapor deposition (MOCVD). 36 After the remaining mask layer was removed, a 300 nm thick SiO 2 layer was deposited on the GaN layer using e-beam evaporation by a shadow mask. The SiO 2 cap layer was used as a protective mask for the selective thermal oxidation process.…”

A Selective Etching Route for Large-Scale Fabrication of β-Ga2O3 Micro-/Nanotube Arrays

“…A 4 µm-thick GaN epitaxial film used in this study was grown on c-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD) [28], and a 200 nmthick SiO 2 protective layer was deposited by plasma enhanced chemical vapor deposition (PECVD) on the GaN epitaxial wafer. The GaN micro-/nanowire arrays were fabricated by the top-down ICP etching process based on Ni masks.…”