Improved MOCVD growth of GaN on Si‐on‐porous‐silicon substrates (original) (raw)
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Characterization of GaN layers grown on porous silicon
Materials Science and Engineering: B, 2001
This work reports the first successful results of the growth of GaN on a porous silicon (PS) substrate. GaN layers have been grown on PS substrates by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. The growth rate (measured by laser reflectometry) was found to be dependent on the growth temperature. The surface morphology and crystallinity of the GaN films were characterized by atomic force microscopy (AFM), and X-ray diffraction (XRD). I-V and C -V characteristics of the GaN/PS structure measured at room temperature are reported. We found that the GaN/PS/Si heterojunction forms a diode-like structure with a rather good rectification behaviour.
Growth of GaN Films on Porous Silicon by MOVPE
physica status solidi (a), 2000
In this work, we report on the growth of GaN films on Porous Silicon (PS) substrates by the Metalorganic Vapour Phase Epitaxy (MOVPE) technique. The growth of GaN has been controlled by in-situ laser reflectometry. The growth rate was found to depend on growth temperature. X-ray Diffraction (XRD) patterns show that the epitaxial films correspond to that of GaN. The morphology and density of the nano-scale GaN layers were determined by atomic force microscopy (AFM) measurements. These first results show that PS is a promising candidate for obtaining GaN films.
Growth of GaN on porous SiC and GaN substrates
Journal of Electronic Materials, 2003
We have studied the growth of GaN on porous SiC and GaN substrates, employing both plasma-assisted molecular beam epitaxy (PAMBE) and metalorganic chemical vapor deposition (MOCVD). For growth on porous SiC, transmission electron microscopy (TEM) observations indicate that the epitaxial GaN growth initiates primarily from surface areas between pores, and the exposed surface pores tend to extend into GaN as open tubes and trap Ga droplets. The dislocation density in the GaN layers is similar to, or slightly less than, that observed in layers grown on non-porous substrates. For the case of GaN growth on porous GaN the overgrown layer replicates the underlying dislocation structure (although considerable dislocation reduction can occur as this overgrowth proceeds, independent of the presence of the porous layer). The GaN layers grown on a porous SiC substrate were found to be mechanically more relaxed than those grown on non-porous substrates; electron diffraction patterns indicate that the former are free of misfit strain or are even in tension after cooling to room temperature. Significant changes in the stress of the overgrown layers on porous GaN were also found, as seen in line shifts of low-temperature photoluminescence spectra.
Characterization of MOCVD grown GaN on porous SiC templates
physica status solidi (c), 2005
We have grown GaN layers by MOCVD on a set of nanoporous SiC templates with different porosity and morphology, produced by etching the anodized porous SiC starting material in a H 2 environment at temperatures ~1500 °C, in an effort to attain improved films. The hydrogen etching serves to remove surface damage caused during mechanical polishing prior to anodization, remove the skin layer associated with anodization, tune the pore size, and consolidate pore geometry. Growth conditions favoring lateral overgrowth of GaN were employed on this set of samples to obtian GaN to a thickness of 2 µm. Atomically smooth surfaces were obtained for the epitaxial GaN layers. The GaN quality is highly dependent on the specifics of the porous templates used. An intensity increase of up to a factor of 30 was observed in the GaN excitonic peak compared to GaN grown on standard SiC substrate. The I-V data indicated significant reduction in the leakage current (in reverse bias) compared to GaN grown on standard SiC. The dependence of optical properties, crystalline quality, and surface morphology on the particulars of porous SiC templates is discussed.
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.
Morphological properties of AlN and GaN grown by MOVPE on porous Si(111) and Si(111) substrates
Superlattices and Microstructures, 2006
Metal Organic Vapour Phase Epitaxy (MOVPE) of AlN and GaN layers at a temperature of 1080 • C were performed on porous Si(111) and Si(111) substrates. The thermal stability of porous silicon (PS) is studied versus growth time under AlN and GaN growth conditions. The surface morphology evolution of the annealed PS is revealed by scanning electron microscopy (SEM). Porous Si(111) with low porosity (40%) is more thermally stable than porous Si(100) with relatively high porosity (60%).
Epitaxial growth of (0001) oriented porous GaN layers by chemical vapour deposition
CrystEngComm, 2014
LEDs with enhanced light extraction efficiency and sensors with improved sensitivity have been developed using porous semiconductors. Here, the growth of porous GaN epitaxial layers oriented along the [0001] crystallographic direction on Al 2 O 3 , SiC, AlN and GaN substrates is demonstrated. A lattice mismatch between the substrate and the porous GaN layer directly affects the structure and porosity of the porous GaN layer on each substrate. Deposition of unintentionally doped n-type porous GaN on non-porous p-type GaN layers allows for the fabrication of high quality rectifying p-n junctions, with potential applications in high brightness unencapsulated GaN-based light emitting diodes and high surface area wide band gap sensor devices.
Optical properties of GaN grown on porous silicon substrate
physica status solidi (a), 2004
A photoluminescence (PL) study of GaN grown on Si(100) substrate using porous silicon (PS) as an intermediate layer is reported. The samples were characterized using PL for the temperature range 5 -300 K under various excitation powers from 5 to 50 mW. For growth temperatures below 800 °C, the room temperature PL shows a broad peak located around cubic GaN emission. This is in clear contradiction with previous scanning electron microscopy and X-ray measurements. At low PL temperature, the observed lines located at 3.306 and 3.364 eV have a narrow full width at half maximum of about 6 and 10 meV, respectively. When the excitation power was varied, no peak shift was observed. These peaks were assigned as deeply localized excitons related to stacking faults near the PS/GaN interface. Quantum confinement (type I or II) due to the presence of nanometric cubic inclusions is another possible explanation for the low-temperature PL.
Porous silicon as an intermediate buffer layer for GaN growth on (100) Si
Microelectronics Journal, 2001
We report preliminary results on the growth of GaN on (100) Si substrate using porous silicon (PS) as an intermediate buffer layer. The growth was in situ monitored by laser beam re¯ectivity. Analysis of the evolution of the re¯ectivity signal indicates a change from relativelȳ at surface to rough one as the growth temperature (T g ) is increased. At a temperature of about 10508C, the growth rate is very low and the re¯ected signal intensity is constant. When the growth temperature is varied, no drastic change of the porosity of the intermediate layer was detected. Scanning electron microscope (SEM) observations of the GaN/SP/Si structure revealed a good surface coverage at 5008C. When T g increases, the structure morphology changes to columnar like structure at 6008C, and well-developed little crystallites with no preferential orientation appear at 8008C. These observations agree well with the X-ray diffraction (XRD) analysis. A preferential hexagonal growth is obtained at low growth temperature, while cubic phase begin to appear at elevated temperatures. q