Optoelectronic Properties of Improved GaN Semiconductor on Si(111) Using Growth Approaches And Different Interlayer′s (original) (raw)
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physica status solidi (a), 2001
High-quality GaN films were grown on Si(111) substrate using 3C-SiC intermediate layer by metalorganic chemical vapor deposition. The 3C-SiC intermediate layer was grown on the Si(111) substrate by chemical vapor deposition using tetramethylsilane as a single source precursor. We have investigated the effect of chemical etching of SiC intermediate layer surface under different conditions. SiC layer was etched using potassium carbonate (K 2 CO 3), hydrochloric acid (HCl), and hydrofluoric acid (HF), respectively. The surface roughness of 3C-SiC intermediate layer decreased as the chemical etching time was increased. GaN films with local atomically flat surfaces were obtained and the X-ray diffraction full-width at half maximum of (0002) peak was 664.5 arcsec for a 1.56 mm thick film. The reduced SiC surface roughness decreased the defect density in GaN epilayers. In the photoluminescence spectra at room temperature, the yellow band emission peak at around 2.2 eV disappeared.
Cubic GaN epilayers grown by molecular beam epitaxy on thin β-SiC/Si (001) substrates
Applied Physics Letters, 2000
The molecular beam epitaxy of cubic GaN on Si͑001͒ substrates, which were covered by a 4 nm thick -SiC layer, is reported. The structural and optical properties of the cubic GaN epilayers were studied by transmission electron microscopy, high-resolution x-ray diffraction, and low-temperature photoluminescence measurements. We find clear evidence for the growth of cubic GaN layers almost free of hexagonal inclusions. The density of extended defects and the near band edge photoluminescence of the cubic GaN layers grown at substrate temperatures of 835°C is comparable to that of high quality cubic GaN epilayers grown by molecular beam epitaxy on GaAs ͑001͒ substrates.
Journal of Crystal Growth, 2002
The initial growth of hexagonal GaN films grown on Si(1 1 1) substrates coated with an ultra-thin SiC buffer layer was studied. It was found that a 2.5-nm-thick SiC layer is an effective buffer layer for GaN growth on an Si(1 1 1) substrate. Under Ga-rich growth conditions, Ga adatoms, in comparison to those under N-rich growth conditions, were highly mobile. Consequently, the GaN films had a flat surface and an almost stacking-fault-free microstructure. The initial GaN nucleations quickly coalesced laterally to submicron-sized grains. Under N-rich growth conditions, the initial GaN nucleations saturated at a diameter of about 50 nm (measured at the film surface). The grown GaN films showed statistical roughening of the surface and a characteristic columnar structure. The yellow-band luminescence (YL) was sensitive to the microstructures of the GaN films prepared under almost the same growth conditions, suggesting that the Ga-vacancy is not the sole source of YL.
Study of the optical and structural properties of GaN films grown on Si substrates with a SiC layer
Thin Solid Films, 2003
GaN films were grown on Si(100) substrates by molecular beam epitaxy employing an RF activated N-plasma source. The substrates were coated with a thin SiC layer to reduce the reaction of N with Si. The substrate temperature was set at 750 8C, and the flux of Ga atoms was varied by changing the Ga-Knudsen cell temperature (T) from 950 to 1100 8C. The effects of Ga the different growth conditions on the optical and structural characteristics of the films were studied by X-ray diffraction, atomic force microscopy, photoluminescence and photoreflectance spectroscopy. The results show that for T s950 8C, the films Ga presented a very poor crystal quality with a mixture of hexagonal (a) and cubic (b) GaN phases. By increasing T the crystal Ga quality improved. The films presented predominately the b-GaN phase for an optimal temperature T of 1050 8C.
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.
Optoelectronic properties of GaN epilayers in the region of yellow luminescence
Journal of Applied Physics, 2006
We studied a GaN epitaxial wafer grown by metal organic chemical vapor deposition, in which a lateral variation in the density of dislocations and associated defects was induced by a special preparation of the GaN buffer layer. Electron beam induced current and photocurrent measurements reveal lateral variations in the electrical properties of the GaN epilayer corresponding to the gradient in the defect density. The photocurrent spectra show four well distinct peaks separating the well known defect related yellow band in a blue, a green, a yellow, and a red component. In particular, we observe a strong dependence of the green component on the density of the a-type threading dislocations. There is evidence that the green and the yellow components are also significantly influenced by point defects.
Engineering and Technology Journal
Grown GAN thin film had a hexagonal crystalline structure and high-intensity peak at the (002) plane. The absorption spectrum of grown GaN film showed a high absorbance at a UV spectrum of 302.88, 435.26 nm. Three methods relations were used to estimate the optical energy gap of prepared P-Si substrate and grown GaN film. The optical energy gap of the P-Si substrate was 2.1 eV, while the grown GaN thin film had a multi-optical energy gap of 3.3 and 1.6 eV. The optical properties of a grown gallium nitride (GaN) thin film on a porous silicon (P-Si) substrate was investigated. A Photo-electrochemical etching method was used to synthesize the Psi substrate, and a physical deposition method (pulsed laser deposition) of 1064 nm Q-switch Nd: YAG laser with a vacuum of 10 −2 mbar was used to grow a thin layer of GaN on a prepared P-Si substrate. X-Ray diffraction displayed that GaN film has a high crystalline nature at the (002) plane. The photoluminescence of GaN film exhibited ultraviolet PL with a peak wavelength of 374 nm corresponding to GaN material and red PL with a peak wavelength of 730 nm corresponding to Psi substrate. The absorption coefficient of the P-Si substrate and grown GaN thin film was obtained from the absorption calculation of UV-Vis diffused spectroscopy at ambient temperature in the 230-1100 nm wavelength range. Extinction coefficients, optical energy gap, and refractive index of both the P-Si substrate and the grown GaN thin film have been determined, respectively. The direct optical energy gaps of both the P-Si substrate and grown GaN have also been determined using three methods: Plank's relation with photoluminescence (PL) spectroscopy, Tauc'relation, and Kubulka-Munk argument with Uv-Vis diffused spectroscopy. It was observed that the optical energy gap of the P-Si substrate was 2.1 eV, while the grown GaN thin film had a multi-optical energy gap of 3.3 eV and 1.6 eV. A good agreement has been obtained between these mentioned methods.
Growing GaN LEDs on amorphous SiC buffer with variable C/Si compositions
Scientific Reports, 2016
The epitaxy of high-power gallium nitride (GaN) light-emitting diode (LED) on amorphous silicon carbide (a-Si x C 1−x) buffer is demonstrated. The a-Si x C 1−x buffers with different nonstoichiometric C/Si composition ratios are synthesized on SiO 2 /Si substrate by using a low-temperature plasma enhanced chemical vapor deposition. The GaN LEDs on different Si x C 1−x buffers exhibit different EL and C-V characteristics because of the extended strain induced interfacial defects. The EL power decays when increasing the Si content of Si x C 1−x buffer. The C-rich Si x C 1−x favors the GaN epitaxy and enables the strain relaxation to suppress the probability of Auger recombination. When the Si x C 1−x buffer changes from Si-rich to C-rich condition, the EL peak wavelengh shifts from 446 nm to 450 nm. Moreover, the uniform distribution contour of EL intensity spreads between the anode and the cathode because the traping density of the interfacial defect gradually reduces. In comparison with the GaN LED grown on Sirich Si x C 1−x buffer, the device deposited on C-rich Si x C 1−x buffer shows a lower turn-on voltage, a higher output power, an external quantum efficiency, and an efficiency droop of 2.48 V, 106 mW, 42.3%, and 7%, respectively. Gallium nitride (GaN) is the most intriguing material beucase it exhibits large bandgap energy and high electronic saturation speed to utilize versatile optoelectronic applications including light-emitting diodes (LEDs) 1 , the laser diodes 2 , solar cells 3 , and field effect transistors 4. Specially, the blue GaN LED has been investigated to favor its important applications in the flat panel display 5 , the white lighting, and the visible light communication 6. In order to further enhance the performance of GaN LEDs, the substrate selection has emerged as a new research topic in recent years. The GaN LED has been considered to fabricate on versatile substrates such as the sapphire 7-9 , silicon (Si) 10-12 , zinc oxide 13-15 , silicon carbide (SiC) 16-18 , and GaN 19-21. In common, the GaN LED is grown on a sapphire substrate because the sapphire substrate shows the high chemical stability at low cost. In 1993, Nakamura et al. fabricated the high-power violet InGaN/GaN LED with its output power and external quantum efficiency of 90 μ W and 0.15%, respectively 7. In addition, Hwang et al. also utilzied the nonpolar GaN LED grown on the r-plane sapphire substrate 8. However, the large lattice mismatch between sapphire and GaN is 16% to degrade the device performance. Alternatively, Yoshida et al. employed the AlN film as buffer layer to improve the performance of strain relaxation 9. The Si substrate becomes another candidate to further decrease the manufacturing cost and large-area fabrication. When the Si substrate is used as the substrate, the GaN LED can be compatible and integrated with Si substrate to form all Si-based optoelectronic devices. In 1998, Guha et al. fabricated the ultraviolet and violet GaN LEDs with the peak wavelengths of 360 nm and 420 nm, respectively 10. Moreover, Tran et al. also tried to fabricate the multiple-quantum-well InGaN/GaN LED on Si substrate 11. In 2006, Dadgar et al. successfully grew the crack-free GaN LED on Si substrate by using the AIN buffer with thickness of 5.4 μ m. Unfortunately, the lattice