34 research outputs found
Distorted wurtzite unit cells: Determination of lattice parameters of non-polar a-plane AlGaN and estimation of solid phase Al content
Unlike c-plane nitrides, ``non-polar" nitrides grown in e.g. the a-plane or
m-plane orientation encounter anisotropic in-plane strain due to the anisotropy
in the lattice and thermal mismatch with the substrate or buffer layer. Such
anisotropic strain results in a distortion of the wurtzite unit cell and
creates difficulty in accurate determination of lattice parameters and solid
phase group-III content (x_solid) in ternary alloys. In this paper we show that
the lattice distortion is orthorhombic, and outline a relatively simple
procedure for measurement of lattice parameters of non-polar group III-nitrides
epilayers from high resolution x-ray diffraction measurements. We derive an
approximate expression for x_solid taking into account the anisotropic strain.
We illustrate this using data for a-plane AlGaN, where we measure the lattice
parameters and estimate the solid phase Al content, and also show that this
method is applicable for m-plane structures as well
Evaluation of Vertical Coherence Length, Twist and Microstrain of GaAs / Si Epilayers Using Modified Williamson-Hall Analysis
Modified Williamson-Hall (WH) analysis is used to determine the reliable values of the microstructures for
Zincblende epilayers grown on non-polar substrates. Systematic high resolution X-ray diffraction (HRXRD) experiments
are performed for several skew symmetric reflections which enable an accurate measurement of the
values of vertical coherence length (VCL) and microstrain of GaAs epilayers grown on Si. Furthermore, a simple
method based on the orientation of Burgers vector is proposed for estimating the ratio of tilt and twist. In this
method, the twist can be found easily once tilt is known. It is rather quick and the measured values of twist are
very similar to those which are otherwise estimated by acquiring numerous HRXRD scans along with tedious
fitting procedures. Presence of 60 mixed dislocations is confirmed from the cross sectional high resolution
transmission electron microscope images of GaAs / Si samples. Furthermore, the estimated value of VCL is
equivalent to the layer thickness measured by the surface profiler.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3598