Results on epitaxial lateral overgrowth of GaAs layers are reported. The methods of controlling the growth anisotropy, the effect of substrate defects filtration in epitaxial lateral overgrowth procedure and influence of the mask on properties of epitaxial lateral overgrowth layers will be discussed. The case of GaAs epitaxial lateral overgrowth layers grown by liquid phase epitaxy on heavily dislocated GaAs substrates was chosen as an example to illustrate the processes discussed. The similarities between our results and those reported recently for GaN layers grown laterally by metallorganic vapour phase epitaxy will be underlined.
X-ray rocking curve imaging technique was used to study crystallographic perfection of laterally overgrown epitaxial structures. We focus on rocking curve imaging studies of Si-doped GaAs and GaSb laterally overgrown layers grown by liquid phase epitaxy on SiO_{2} masked GaAs and GaSb/GaAs substrates, respectively. High spatial resolution offered by rocking curve imaging technique allows studying the effect of laterally overgrown epitaxial wing tilt towards the mask. Distribution of tilt magnitude over the area of laterally overgrown epitaxial stripes is easily determined. In heteroepitaxial GaSb/GaAs laterally overgrown epitaxial structures local mosaicity in the wing area was detected. Since individual grains are clearly visible on rocking curve imaging maps, their size and relative misorientation can be determined.
Spatially resolved X-ray diffraction is introduced and applied for micro-imaging of strain in GaAs and GaSb layers grown by epitaxial lateral overgrowth on GaAs substrates. We show that laterally overgrown parts of the layers (wings) are tilted towards the underlying mask. By spatially resolved X-ray diffraction mapping the direction of the tilt and distribution of tilt magnitude across the width of each layer can be readily determined. This allows measuring of the shape of the lattice planes in individual epitaxial stripes. In GaSb/GaAs heteroepitaxial laterally overgrown layers local mosaicity in the wing area was found. By spatially resolved X-ray diffraction the size of microblocks and their relative misorientation were analyzed. Finally, microscopic curvature of lattice planes confined between two neighboring slip bands in thermally strained Si wafers is measured. All these examples show advantages of spatially resolved X-ray diffraction over a standard X-ray diffraction when applied for analysis of crystalline microstructures.
In this work we present analysis of carriers dynamics in samples of GaN nanowires grown on silicon. The samples exhibit bright luminescence of bulk donor-bound excitons at 3.472 eV, surface defect-bound excitons at 3.450 eV (SDX) and a broad (0.05 eV) band centered at 3.47 eV caused probably by single free exciton and bi-exciton recombination. The SDX emission has long lifetime τ = 0.6 ns at 4 K and can be observed up to 50 K. At higher temperatures luminescence is dominated by free excitons. The broad excitonic band is best visible under high excitation, and reveals fast, non-exponential dynamics. We present mathematical model assuming exciton-exciton interaction leading to the Auger processes. The model includes n^2 (Langevin) term and describes well the non-exponential dynamics of the excitonic band.
We report on growth of GaN nanocolumns by plasma assisted MBE on (111) silicon substrates and on their characterization. The nanocolumns nucleate on the substrate spontaneously without use of any catalyst, probably by the Volmer-Weber mechanism. Transmission electron microscopy analysis shows high crystalline quality of GaN nanocolumns and their good alignment with the c-axis being perpendicular to the substrate. Preliminary results on use of GaN nanocolumns in gas sensor devices are presented.
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