Nomarski microscopy images from the surfaces of Si-doped GaN/AlGaN films. Clearly, the increase of Al content or Si content leads to the cracked epilayers.
scans of the (006)-reflection of the films with different Si concentrations. The c-lattice constant of the doped films shrinks with increasing Si concentration.
RSM of (105) reflection from samples A, B, C, and D (): An increase of the a-lattice constant ( of the doped layers in comparison to the undoped AlGaN buffer layer is visible. The opposite scenario is valid for the c-lattice constants (, correlating with the symmetric HRXRD measurements in Fig. 2.
RSM of (105) reflection from the Si-doped GaN epilayer (sample Ein Fig. 6) with a nominal Si content of . Similar to the case of AlGaN:Si films (Fig. 3), GaN:Si films have visibly a larger a-lattice constant compared to that of undoped GaN buffer layer, as shown schematically in the inset.
Schematic structure of samples S and W. Sample (W) without the nano-mask has a significantly higher density of edge-type dislocations.
Nomarski microscopy images from the surfaces of the two heavily Si-doped AlGaN films: samples S and W.
Weak beam dark field TEM micro-graphs of sample S. The yellow line indicates the interface between the undoped buffer and the doped top-layer. The top and bottom images are from the same sample area showing edge/mixed dislocation and screw/mix dislocations, respectively. Almost all dislocations are of edge-type, getting inclined at the beginning of doping.
In-situ measured temperature and reflectance () of samples S and W during growth. The dotted arrows denote the beginning of the Si-doping for each sample.
The corrected in-situ curvature measurement of samples S and W. The strain of every epilayer during the growth was calculated using Stoney formula (Eq. (1)).
Room temperature ex-situ RSM of samples S and W recorded by the (105) reflection, showing similar strain situation as the in-situ recorded curvature in Fig. 9.
Strain dipole around an edge type dislocation (extra half plane) plotted without the prefactors in Eq. (2).
Microphotoluminescence area scan around an edge dislocation across the surface of an undoped GaN sample. The contour plots depict the energy deviations of the near-band-edge PL from the same region. An almost symmetric strain dipole around the dislocation is visible.
Microphotoluminescence area scan across the surface of a Si doped GaN sample. Dislocations appear as dark spots (number 1–4) in the images of the integrated near-band-edge intensity. The adjacent contour plots depict the energy deviations of the near-band-edge PL from the same region. Formation of asymmetric strain dipoles due to the reduction of compressive pole is visible.
Two possible directions for dislocation climb, both resulting from a series of dislocation jogs during growth. The response of an edge-type dislocation to compressive (left) and tensile strain (right) by climbing “backward” and “forward,” respectively.
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