Dislocation reduction in GaN grown on porous TiN networks by metal-organic vapor-phase epitaxy (original) (raw)
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Applied Physics Letters, 2005
We report on the reduction of threading dislocations in GaN overlayers grown by organometallic vapor phase epitaxy on micro-porous TiN networks. These networks were obtained by in situ annealing of thin Ti layers deposited in a metalization chamber, on the ͑0001͒ face of GaN templates. Observations by transmission electron microscopy indicate dislocation reduction by factors of up to 10 in GaN layers grown on TiN networks compared with the control GaN. X-ray diffraction shows that GaN grown on the TiN network has a smaller ͑102͒ plane peak width ͑4.6 arcmin͒ than the control GaN ͑7.8 arcmin͒. In low temperature photoluminescence spectra, a narrow excitonic full-width-at-half-maximum of 2.4 meV was obtained, as compared to 3.0 meV for the control GaN, confirming the improved crystalline quality of the overgrown GaN layers.
Reduction of threading dislocation density in GaN grown on strain relaxed nanoporous GaN template
2007
Although suitable for the reduction of the threading dislocation density in GaN layers the widely used two-step MOCVD method does not work as efficiently for AlGaN. This is due to slow surface diffusion of the Al species. In the present paper, the previously reported in situ multistep method for MOCVD growth of high-quality GaN films is adopted for the growth of Al 0.12 Ga 0.88 N films on c-plane sapphire. The developed method for AlGaN growth is virtually GaN free in the sense that no continuous film of GaN is needed near the substrate interface. Crack-free layers of Al 0.12 Ga 0.88 N with a thickness of about 2 mm are grown by the method. A sparse distribution of 3D GaN nucleation islands and stimulation of threading dislocation reactions enable a reduction of the threading dislocation density down to 5 Â 10 8 cm À2 in the Al 0.12 Ga 0.88 N films. The threading dislocation density is evaluated by etch-pit density measurements. Highresolution X-ray diffraction and transmission electron microscopy are used to study the crystallinity of the Al 0.12 Ga 0.88 N layers. Reflectometry is utilized to analyze film growth in situ. The surface morphology of GaN nucleation layers and Al 0.12 Ga 0.88 N epilayers is characterized by atomic force microscopy. r
Dislocation density reduction in GaN using porous SiN interlayers
physica status solidi (a), 2005
The influence of a thin porous SiN X interlayer on the growth of GaN by metalorganic chemical vapor deposition (MOCVD) has been studied. The interlayer is deposited on a GaN template by introducing silane in the presence of ammonia into the MOCVD chamber, and a GaN overlayer is deposited on the interlayer. The SiN X interlayer produces inhomogeneous nucleation and lateral growth of the overlayer, causing bending of dislocations towards facet walls, and it also blocks some dislocations from entering the overlayer. The dislocation density for a GaN overlayer grown on a SiN X interlayer was reduced to 7 × 10 8 cm-2 , which is an order of magnitude less than that for a control sample grown without an interlayer.
Design and fabrication of enhanced lateral growth for dislocation reduction in GaN using nanodashes
Journal of Crystal Growth, 2017
The semiconductor gallium nitride is the material at the centre of energy-efficient solid-state lighting and is becoming increasingly important in high-power and high-frequency electronics. Reducing the dislocation density of gallium nitride planar layers is important for improving the performance and reliability of devices, such as light-emitting diodes and high-electron-mobility transistors. The patterning of selective growth masks is one technique for forcing a three-dimensional growth mode in order to control the propagation of threading defects to the active device layers. The morphology of the three-dimensional growth front is determined by the relative growth rates of the different facets that are formed, and for GaN is typically limited by the slow-growing {1 À1 0 1} facets. We demonstrate how the introduction of nanodash growth windows can be oriented in an array to preserve fast-growing {1 1 À2 2} facets at the early stage of growth to accelerate coalescence of three-dimensional structures into a continuous GaN layer. Cathodoluminescence and Electron Channelling Contrast Imaging methods, both used to measure the threading dislocation density, reveal that the dislocations are organised and form a distinctive pattern according to the underlying mask. By optimising the arrangement of nanodashes and the nanodash density, the threading dislocation density of GaN on sapphire epilayers can be reduced significantly from 10 9 cm À2 to 3.0 Â 10 7 cm À2. Raman spectroscopy, used to monitor the strain in the overgrown GaN epilayers, shows that the position of the GaN E 2 H phonon mode peak was reduced as the dash density increases for a sample grown via pendeo-epitaxy whilst no obvious change was recorded for a sample grown via more conventional epitaxial lateral overgrowth. These results show how growth mask design can be used to circumvent limitations imposed by the growth dynamics. Moreover, they have revealed a greater understanding of the influence of the growth process on the dislocation density which will lead to higher performing electronic and optoelectronic devices as a result of the lower dislocation densities achieved.
Reduction of dislocation density in heteroepitaxial GaN: role of SiH4 treatment
Journal of Crystal Growth, 2004
TEM and AFM data show that a significant reduction of threading dislocations in heteroepitaxial GaN/Al 2 O 3 grown by MOCVD has been achieved. The reduction has been obtained by growth interruption followed by annealing in silane (SiH 4 ). Density of threading dislocations in the GaN layer above the silane-exposed surface decreased to 5 Â 10 7 cm À2 in comparison to 10 9 cm À2 in the layer below this surface. TEM data showed the existence of pyramidal pits at the silane-exposed surface. They were overgrown by the subsequent GaN layer. The presence of these pits indicates that the GaN surface was selectively etched during the silane flow. These pits were sites where dislocations drastically changed propagation direction from parallel to the c-axis to horizontal. Horizontal propagation of dislocations above the surface treated by silane (where formation of SiN was expected) suggests that the GaN layer in this region was grown in the lateral epitaxial overgrowth mode. EDX measurements performed at the interface between the SiH 4 -treated GaN layer and the subsequently grown GaN did not show any presence of Si. Therefore, it is believed that the dislocation reduction is related to the lateral overgrowth above the pits and not to the formation of a SiN interlayer. r
Gallium Nitride Materials and Devices, 2006
We report on the structural, electrical, and optical characterization of GaN epitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) on SiN x and TiN x porous templates in order to reduce the density of extended defects. Observations by transmission electron microscopy (TEM) indicate an order of magnitude reduction in the dislocation density in GaN layers grown on TiN x and SiN x networks (down to ~10 8 cm -2 ) compared with the control GaN layers. Both SiN x and TiN x porous network structures are found to be effective in blocking the threading dislocation from penetrating into the upper layer. Supporting these findings are the results from X-Ray diffraction and low-temperature photoluminescence (PL) measurements. The linewidth of the asymmetric X-Ray diffraction (XRD) (1012) peak decreases considerably for the layers grown using SiN x and TiN x layers, which generally suggests the reduction of edge and mixed threading dislocations. In general, further improvement is observed with the addition of a second SiN x layer. The room temperature decay times obtained from biexponential fits to time-resolved photoluminescence (TRPL) data are increased with the inclusion of SiN x and TiN x layers. TRPL results suggest that primarily point-defect and impurity-related nonradiative centers are responsible for reducing the lifetime. The carrier lifetime of 1.86 ns measured for a TiN x network sample is slightly longer than that for a 200 µm-thick high quality freestanding GaN. Results on samples grown by a new technique called crack-assisted lateral overgrowth, which combines in situ deposition of SiN x mask and conventional lateral overgrowth, are also reported.