AFM pictures of GaN nanostructures (nominal GaN ML) grown with increasing the ammonia beam equivalent pressure ( BEP) during the growth interruption procedure: (a) BEP , (b) BEP , and (c) BEP .
AFM images of (a) GaN quantum dashes (nominal GaN ML and BEP ) and (b) GaN quantum dots (nominal GaN ML and BEP ).
Plane-view schematics of the shape of dot-type (a) and dash-type (b) islands used to calculate the ratio area/volume of the different nanostructures.
Low temperature photoluminescence spectra (8 K) and corresponding photographs of the light emitted from the different samples of QDots (a) and QDashes (b) as a function of the nominal GaN thickness. The samples were excited by an unfocused frequency-doubled Ar laser at an excitation power of .
High-resolution off-axis TEM images of two neighboring GaN QDs embedded in an matrix for samples with: (a) a nominal GaN thickness of 8 ML, with QD heights of 3.5 and 4.1 nm, for the left-side and the right-side QDs, respectively; and (b) a nominal GaN thickness of 12 ML, with QD height of 5.3 and 5.1 nm, for the left-side and the right-side QDs, respectively.
High-resolution off-axis TEM image of two GaN QDashes embedded in an matrix (for a nominal GaN deposited thickness of 12 ML): the height and lateral dimensions are 6.1 and 35.5 nm, and 5.8 and 53.8 nm for the left-side and the right-side QDashes, respectively.
Calculated transition energies as a function of the nanostructure average height (including the wetting layer thickness) for different electric field values . Comparison with the experimental data of GaN QD (black squares) and QDash (empty circles) PL energies. The QD height was measured by TEM and the QDash height was deduced by considering a similar height variation than for QDs. Black dashed lines are guides to the eye.
Dimensions and densities (determined by AFM) of GaN nanostructures grown on as a function of their shape (nominal GaN ML). corresponds to the diameter of the dot. The letters (A, B, and C) refer to the different samples and the corresponding nanostructure density is reported as a function of the island shape.
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