Direct measurement of twist mosaic in GaN epitaxial films as a function of growth temperature

Abstract

Direct measurements of the mosaic twist in GaN films have been carried out using grazing incidence in-plane x-ray diffraction (GIIXD) on a commercially-available diffractometer in the laboratory. The GaN 11.0 in-plane diffraction was measured to obtain the twist mosaic directly, while the GaN 00.2 surface-symmetric rocking curve was used to measure the tilt mosaic. For GaN growth temperatures between 1002°C and 1062°C, the tilt mosaic decreased monotonically with increased temperature, while the twist mosaic showed a minimum at 1022°C, a temperature previously selected empirically as giving the best device yield and optimum optical domain size. A substantial fall in twist and tilt mosaic was observed on annealing of the nucleation layers, the lowest twist mosaic occurring at an annealing temperature of 1002°C, where it was almost equal to the tilt mosaic. A weak minimum in the tilt mosaic variation was seen at an annealing temperature of 1023°C.

Effect of thickness on structural and electrical properties of GaN films grown on SiN-treated sapphire

“…For all the growth stages, the twist mosaic is greater than the tilt mosaic, and the Ayers' model fit [20] shows that the ratio between edge and screw dislocation densities is constant with layer thickness, as also found in Ref. [14] (mixed-type dislocations excluded since the density of these is expected to be very low, as found by Metzger et al [21]). The ratio of edge to screw dislocations is $4.671-lower than has been previously reported.…”

“…To check the reliability of the extrapolated values, GIIXD was used for the direct measurement of in plane twist mosaic. The method was successfully used in previous works [14][15][16]. Fig.…”

“…X-ray measurements were performed with high-resolution diffractometer equipped with a fourfold Ge (2 2 0) monochromator, delivering a pure CuKa 1 line of wavelength (l ¼ 0.154 nm). The GIIXD geometry was detailed in previous works [14][15][16]. Hall effect measurements were conducted by using the standard Van der Pauw configuration.…”

Influence of alloy composition and interlayer thickness on twist and tilt mosaic in AlxGa1−xN/AlN/GaN heterostructures

“…Similarly, in the GIIXD measurements, the shape and FWHM of the 10.0, 20.0 and 11.0 rocking curves were almost equal, showing that the FWHM here determines the twist mosaic, associated with threading edge dislocations. 9 In GIIXD, where the incident beam incidence angle is below the critical angle for total external reflection, the evanescent wave does not penetrate more than a few nanometers and the 11.0 reflection rocking curve FWHM corresponds to the value of the twist mosaic spread of the AlGaN buffer. We note in Fig.…”

“…Our measurements show that the FWHM is constant in angular space. 9 If the reduction in domain size results in an increased FWHM, then it must also indicate an increase in the threading edge dislocation density associated with the smaller diffracting element boundaries.…”