Evolution of the mosaic structure in InGaN layer grown on a thick GaN template and sapphire substrate

Abstract

Cataloged from PDF version of article.The InxGa1-xN epitaxial layers, with indium (x) concentration changes between 0.16 and 1.00 (InN), were grown on GaN template/(0001) Al2O3 substrate by metal organic chemical vapour deposition. The indium content (x), lattice parameters and strain values in the InGaN layers were calculated from the reciprocal lattice mapping around symmetric (0002) and asymmetric (10-15) reflection of the GaN and InGaN layers. The characteristics of mosaic structures, such as lateral and vertical coherence lengths, tilt and twist angle and heterogeneous strain and dislocation densities (edge and screw dislocations) of the InGaN epilayers and GaN template layers were investigated by using high-resolution X-ray diffraction (HR-XRD) measurements. With a combination of Williamson-Hall (W-H) measurements and the fitting of twist angles, it was found that the indium content in the InGaN epilayers did not strongly effect the mosaic structures' parameters, lateral and vertical coherence lengths, tilt and twist angle, or heterogeneous strain of the InGaN epilayers

Buffer effects on the mosaic structure of the HR-GaN grown on 6H-SiC substrate by MOCVD

“…In order to precisely determine the lattice constants (a and c) of the hexagonal GaN crystal, the symmetric and skew symmetric XRD 2h/x-scans can be used in Eq. 1with combining Bragg's law (nk = 2d hkl sin h) [17][18][19].…”

“…Because of two unknowns (a and c) in Eq. 1, at least two different plane reflections (d hkl ) measurements are needed [17][18][19].The symmetric and skew symmetric x-2h scans for all basic crystallographic directions were measured. Generally, lattice constants c of the layer perpendicular to the interface are calculated from the one or two high-angle symmetric (000l) reflections such as (0004), (0006), and (0008) plane measurements.…”

“…Generally, lattice constants c of the layer perpendicular to the interface are calculated from the one or two high-angle symmetric (000l) reflections such as (0004), (0006), and (0008) plane measurements. On the other hand, the lattice constants a parallel to the film interface can be derived using the one or two diffraction peaks of the highangle asymmetrical reflections, such as (10)(11)(12)(13)(14), (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24), (10)(11)(12)(13)(14)(15), and (20-24) [17][18][19]. In this study, the c and a values calculated from the (0004), (0006) symmetric plane reflections, and (10-12), (10-13), (10)(11)(12)(13)(14), and (20-21) asymmetric plane reflections measurements, respectively.…”

“…As it is known, the crystal system of the GaN is the wurtzite hexagonal [17][18][19][20][21]. When a GaN epitaxial layer is grown on a SiC substrate it is form a columnar mosaic structure [17][18][19]. The axes of the hexagonal shape columns is coincide with the crystallographic c-axis of GaN film and these columns are oriented about the c-direction of the SiC substrate with an effective small angle of about a few arcminutes.…”

“…For this reason, the GaN epilayer exhibits in-plane isotropic elastic properties, and its in-plane deformation state can be described by one strain component. Therefore, in-plane strain (e a ) and out-of-plane (e c ) strain components of the GaN epileyers can be calculated by the equations given below [17][18][19][20][21],…”