Efficacy of single and double SiN[sub x] interlayers on defect reduction in GaN overlayers grown by organometallic vapor-phase epitaxy (original) (raw)
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MRS Internet Journal of Nitride Semiconductor Research
Discrete and coalesced monocrystalline GaN and AlxGa1−xN layers grown via pendeo-epitaxy (PE) originated from side walls of GaN seed stripes with and without SiNx top masks have been grown via organometallic vapor phase deposition on GaN/AlN/6H-SiC(0001) and GaN(0001)/AlN(0001)/3C-SiC(111)/Si(111) substrates. Scanning and transmission electron microscopies were used to evaluate the external microstructures and the distribution of dislocations, respectively. The dislocation density in the laterally grown sidewall regions and in the regions grown over the SiNx masks was reduced by at least five orders of magnitude relative to the initial GaN seed layers. Tilting of 0.2° in the coalesced GaN epilayers grown over the SiNx masks was determined via X-ray and selected area diffraction; however, tilting was not observed in the material suspended above the SiC substrate and that grown on unmasked stripes. A strong, low-temperature photoluminescence band-edge peak at ~3.45 eV with a FWHM of &...
Reduction of the dislocation density in HVPE-grown GaN epi-layers by an in situ SiNx treatment
Journal of Crystal Growth, 2010
A new method has been approached to reduce the dislocation density in hydride vapor phase epitaxy (HVPE)-grown GaN epi-layers. By this method, state of the art quality, GaN layers were grown on sapphire substrates with an in situ treatment of SiN x in HVPE process. It was found out that the in situ treatment worked most effectively when introduced after the deposition of the nucleation layer (NL). Amorphous SiN x served as a mask allowing only selective growth of GaN seeds as confirmed by scanning electron microscopy (SEM) analysis and thus a reduction of the dislocation density (down to 10 6 cm À 2) with one order of magnitude lower compared to the standard samples (grown without the SiN x treatment) was obtained. Transmission electron microscopy (TEM) studies revealed that dislocations with a mixed (both screw and edge component) character mostly thread into the GaN layer. Low-temperature photoluminescence showed good optical quality of the layers grown with optimal position of SiN x treatment.
Materials Science and Engineering: B, 2000
GaN films of different thicknesses grown on 6H-SiC (00.1) by hydride vapor-phase epitaxy(HVPE) method were characterized by high resolution X-ray diffractometry and synchrotron X-ray topography. Calculations of thermal stresses gave approximately same results as experimental stress indicating that most of the stress in the film is due to the difference in thermal expansion coefficient between the film and substrate. The lowest dislocation density (i.e. 6.64 ×10 8 cm − 2) in GaN was estimated for the sample, which has the highest thickness of GaN layer. Also comparing two different 6H-SiC substrates grown by sublimation and Lely techniques, the substrate grown by sublimation was found to be the better substrate to grow GaN thin film with lower dislocation density. Synchrotron X-ray topography revealed a number of defects including mosaic structure or local bending, low angle grain boundaries, cracks and micropores. Micropores originated at the 6H-SiC substrate went all the way through GaN films as revealed in the reflection topographs.
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
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.
Current Applied Physics, 2009
In the present paper, the effects of nitridation on the quality of GaN epitaxial films grown on Si(1 1 1) substrates by metal-organic chemical vapor phase deposition (MOCVD) are discussed. A series of GaN layers were grown on Si(1 1 1) under various conditions and characterized by Nomarski microscopy (NM), atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD), and room temperature (RT) photoluminescence (PL) measurements. Firstly, we optimized LT-AlN/HT-AlN/Si(1 1 1) templates and graded AlGaN intermediate layers thicknesses. In order to prevent stress relaxation, step-graded AlGaN layers were introduced along with a crack-free GaN layer of thickness exceeding 2.2 lm. Secondly, the effect of in situ substrate nitridation and the insertion of an Si x N y intermediate layer on the GaN crystalline quality was investigated. Our measurements show that the nitridation position greatly influences the surface morphology and PL and XRD spectra of GaN grown atop the Si x N y layer. The X-ray diffraction and PL measurements results confirmed that the single-crystalline wurtzite GaN was successfully grown in samples A (without Si x N y layer) and B (with Si x N y layer on ). The resulting GaN film surfaces were flat, mirror-like, and crack-free. The full-width-at-half maximum (FWHM) of the X-ray rocking curve for (0 0 0 2) diffraction from the GaN epilayer of the sample B in x-scan was 492 arcsec. The PL spectrum at room temperature showed that the GaN epilayer had a light emission at a wavelength of 365 nm with a FWHM of 6.6 nm (33.2 meV). In sample B, the insertion of a Si x N y intermediate layer significantly improved the optical and structural properties. In sample C (with Si x N y layer on Al 0.11 Ga 0.89 N interlayer). The in situ depositing of the, however, we did not obtain any improvements in the optical or structural properties.
Studies of Defect Structure in Epitaxial AlN/GaN Films Grown on (111) 3C-SiC
Nanomaterials
Several aspects such as the growth relation between the layers of the GaN/AlN/SiC heterostructure, the consistency of the interfaces, and elemental diffusion are achieved by High Resolution Transmission Electron Microscopy (HR-TEM). In addition, the dislocation densities together with the defect correlation lengths are investigated via High-Resolution X-ray Diffraction (HR-XRD) and the characteristic positron diffusion length is achieved by Doppler Broadening Spectroscopy (DBS). Moreover, a comparative analysis with our previous work (i.e., GaN/AlN/Si and GaN/AlN/Al2O3) has been carried out. Within the epitaxial GaN layer defined by the relationship F4¯3m (111) 3C-SiC || P63mc (0002) AlN || P63mc (0002) GaN, the total dislocation density has been assessed as being 1.47 × 1010 cm−2. Compared with previously investigated heterostructures (on Si and Al2O3 substrates), the obtained dislocation correlation lengths (Le = 171 nm and Ls =288 nm) and the mean distance between two dislocation...
MRS Proceedings, 2005
An alternative scheme to the growth of crack free, dislocation reduced III-Nitride layers on Silicon substrate has been previously introduced that relies on formation of an ion implanted defective layer in the substrate with implantation taking place in the presence of AlN buffer layer. Here, the effects of N+ ion implantation of AlN/Si (111) substrate on the structural and optical properties of the overgrown GaN epilayers have been investigated. Temperature dependent photoluminescence has been used to investigate the impact of the implantation conditions (energy and dose) on optical and structural quality of the GaN overgrown layers. A correlation between PL and high resolution x-ray diffraction (XRD) of the overgrown GaN layers show that the lowest FWHM of bandedge, the highest bandedge to deep defect blue luminescence band ratio, and the lowest symmetric rocking curve FWHM are achieved for the optimized implantation conditions. This correlates well with the results of etch pit de...
Applied Physics Letters, 2007
Significant improvement of structural and optical qualities of GaN thin films on sapphire substrates was achieved by metal organic chemical vapor deposition with in situ SiN x nanonetwork. Transmission electron microscope ͑TEM͒ studies revealed that screw-and edge-type dislocations were reduced to 4.4ϫ 10 7 and 1.7ϫ 10 7 cm −2 , respectively, for a ϳ5.5-m-thick layer. Furthermore, room temperature carrier lifetimes of 2.22 and 2.49 ns were measured by time-resolved photoluminescence ͑TRPL͒ for samples containing single and double SiN x network layers, respectively, representing a significant improvement over the previous studies. The consistent trends among the TEM, x-ray diffraction, and TRPL measurements suggest that in situ SiN x network reduces line defects effectively as well as the point-defect-related nonradiative centers.
Journal of Crystal Growth, 2002
We studied the initial growth of Si-doped GaN (GaN:Si) epilayers grown under both N-and Ga-rich conditions. Upon Si doping, the surface polarity changed from N-to Ga-polarity. The surface diffusion kinetics of the Ga adatoms of the GaN:Si epilayers depended strongly on the Ga/N flux ratio. GaN:Si films with good crystal quality were obtained for a Ga/N flux ratio slightly larger than 1. The dislocation density decreased about one order of magnitude, while the stacking fault and cubic phase density near the interfacial region increased. The main types of dislocations in the undoped GaN were mixed and edge dislocations. In the GaN:Si, the main dislocations were pure-edge dislocations. The dislocation-density reduction in the GaN:Si may have been due to a low density of mixed dislocations in the presence of a high density of stacking faults and cubic phase.