Mengyao Xie

Effects of strain and composition on the lattice parameters and applicability of Vegard's rule in Al-rich Al1-xInxN films grown on sapphire

The lattice parameters and strain evolution in Al1−xInxN films with 0.07⩽x⩽0.22 grown on GaN-buffered sapphire substrates by metal organic vapor phase epitaxy have been studied by reciprocal space mapping. Decoupling of compositional effects on the strain determination was accomplished by measuring the In contents in the films both by Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). Differences between XRD and RBS In contents are discussed in terms of compositions and biaxial strain in the films. It is suggested that strain plays an important role for the observed deviation from Vegard’s rule in the case of pseudomorphic films. On the other hand, a good agreement between the In contents determined by XRD and RBS is found for Al1−xInxN films with low degree of strain or partially relaxed, suggesting applicability of Vegard’s rule in the narrow compositional range around the lattice matching to GaN.

Lattice parameters, deviations from Vegard’s rule, and E2 phonons in InAlN

The lattice parameters of InxAl1-xN in the whole compositional range are studied using first-principle calculations. Deviations from Vegards rule are obtained via the bowing parameters, delta(a)=0. ...

Structural anisotropy of nonpolar and semipolar InN epitaxial layers

We present a detailed study of the structural characteristics of molecular beam epitaxy grown nonpolar InN films with a- and m-plane surface orientations on r-plane sapphire and (100) γ-LiAlO2, respectively, and semipolar (101¯1) InN grown on r-plane sapphire. The on-axis rocking curve (RC) widths were found to exhibit anisotropic dependence on the azimuth angle with minima at InN [0001] for the a-plane films, and maxima at InN [0001] for the m-plane and semipolar films. The different contributions to the RC broadening are analyzed and discussed. The finite size of the crystallites and extended defects are suggested to be the dominant factors determining the RC anisotropy in a-plane InN, while surface roughness and curvature could not play a major role. Furthermore, strategy to reduce the anisotropy and magnitude of the tilt and minimize defect densities in a-plane InN films is suggested. In contrast to the nonpolar films, the semipolar InN was found to contain two domains nucleating on zinc-blende InN(11...

Effect of Mg doping on the structural and free-charge carrier properties of InN films

We study the structural and free-charge carrier properties of two sets of InN films grown by molecular beam epitaxy doped with different Mg concentrations from 1x1018 cm-3 to 3.9x1021 cm-3. We dete ...

Unintentional incorporation of hydrogen in wurtzite InN with different surface orientations

We have studied hydrogen impurities and related structural properties in state-of-the-art wurtzite InN films with polar, nonpolar, and semipolar surface orientations. The effects of thermal annealing and chemical treatment on the incorporation and stability of H are also discussed. The near-surface and bulk hydrogen concentrations in the as-grown films increase when changing the surface orientation from (0001) to (0001¯) to (11¯01) and to (112¯0), which may be associated with a decrease in the grain size and change of the growth mode from 2D to 3D. Thermal annealing at 350oC in N2 leads to a reduction of H concentrations and the intrinsic levels of bulk H are found to correlate with the structural quality and defects in the annealed films.

Unravelling the free electron behavior in InN

Precise measurement of the optical Hall effect in InN using magneto-optical generalized ellipsometry at IR and THz wavelengths, allows us to decouple the surface accumulation and bulk electron densities in InN films by non-contact optical means and further to precisely measure the effective mass and mobilities for polarizations parallel and perpendicular to the optical axis. Studies of InN films with different thicknesses, free electron densities and surface orientations enable an intricate picture of InN free electron properties to emerge. Striking findings on the scaling factors of the bulk electron densities with film thickness further supported by transmission electron microscopy point to an additional thickness dependent doping mechanism unrelated to dislocations. Surface electron accumulation is observed to occur not only at polar but also at non-polar and semi-polar wurtzite InN, and zinc blende InN surfaces. The persistent surface electron density shows a complex behavior with bulk density and surface orientation. This behavior might be exploited for tuning the surface charge in InN.