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1.
In this work, we have comparatively investigated the effects of the GaN, AlGaN, and AlN low-temperature buffer layers (BL)
on the crystal quality of a-plane GaN thin films grown on r-plane sapphire substrates. Scanning electron microscopy images of the a-plane GaN epilayers show that using an AlGaN BL can significantly reduce the density of surface pits. The full-width at half-maximum
values of the x-ray rocking curve (XRC) are 0.19°, 0.36°, and 0.48° for the films grown using Al 0.15Ga 0.85N, GaN, and AlN BLs, respectively, indicating that an AlGaN BL can effectively reduce the mosaicity of the films. Room-temperature
photoluminescence shows that the AlGaN BL results in lower impurity incorporation in the subsequent a-plane GaN films, as compared with the case of GaN and AlN BLs. The higher crystal quality of a-plane GaN films produced by the Al 0.15Ga 0.85N BL could be due to improvement of BL quality by reducing the lattice mismatch between the BL and r-sapphire substrates, while still keeping the lattice mismatch between the BL and epitaxial a-plane GaN films relatively small. 相似文献
2.
Porous and sub‐micrometer tubes made of textured GaN nanoparticles have been synthesized by an in situ chemical reaction and characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) and Raman spectroscopies. The in situ reaction involves thermal decomposition and nitridation of 1D gallium oxyhydroxide (GaOOH) at temperatures in the range of 700–900 °C. The 1D shape of the precursor GaOOH is maintained in the resultant GaN tubes. The GaN nanocrystals (estimated to be about 15 nm in size) are found to be highly oriented with respect to each other in the tube structure, with the [110] GaN direction parallel to the tube axis. The growth mechanism of the tube structure has also been studied. β‐Ga 2O 3 is found to be an intermediate phase between the starting GaOOH precursor and the final GaN product. The growth mechanism involves decomposition of GaOOH, which produces β‐Ga 2O 3 tubes with hollow interiors, and nitridation of β‐Ga 2O 3, which leads to growth of textured GaN nanocrystals. Based on the growth mechanism, tubular structures with either quasi‐circular or rectangular cross section are selectively synthesized by controlling the heating rate and calcination temperature. This in situ chemical reaction method provides a new route for synthesizing 1D hollow nanostructures. 相似文献
3.
High-resolution X-ray diffraction (HR-XRD) with rocking curve, atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy have been performed on high-quality quaternary Al xIn yGa 1−x−yN thin films at room temperature. The Al xIn yGa 1−x−yN films were grown on c-plane (0 0 0 1) sapphire substrates with AlN as buffer layers using a molecular beam epitaxy (MBE) technique with aluminum (Al) mole fractions x ranging from 0.0 to 0.2 and constant indium (In) mole fraction y=0.1. HR-XRD measurements confirmed the high crystalline quality of these alloys without any phase separation. The X-ray rocking curve of Al xIn yGa 1−x−yN films typically shows full widths at half maximum (FWHM) intensity between 14.4 and 28.8 arcmin. AFM measurements revealed a two-dimensional (2D) growth mode with a smooth surface morphology of quaternary epilayers. PL spectra exhibited both an enhancement of the integrated intensity and an increasing blueshift with increased Al content with reference to the ternary sample In 0.1Ga 0.90N. Both effects arise from Al-enhanced exciton localization. PL was used to determine the behavior of the energy band gap of the quaternary films, which was found to increase with increasing Al composition from 0.05 to 0.2. This trend is expected since the incorporation of Al increases the energy band gap of ternary In 0.1Ga 0.90N (3.004 eV). We have also investigated the bowing parameter for the variation of energy band gaps and found it to be very sensitive on the Al composition. A value of b=10.4 has been obtained for our quaternary Al xIn yGa 1−x−yN alloys. 相似文献
4.
Al xGa 1−xN/GaN/AlN heterostructures on silicon (Si) substrate was developed by nitrogen plasma-assisted molecular beam epitaxy (MBE) and their properties were investigated by scanning electron microscopy (SEM), electron dispersive X-ray (EDX), atomic force microscopy (AFM), high resolution X-ray diffraction (XRD), Raman spectroscopy and Hall effect measurements. High purity gallium (7N) and aluminum (6N5) were used in the Knudsen cells. High purity nitrogen with 7N purity was supplied to radio frequency (RF) source to generate reactive nitrogen species. The nitrogen pressure and a discharge power were kept at 1.5×10 −5 Torr and 300 W, respectively. From SEM measurements, the surface morphology of samples presented 2- and 3-dimensional growth modes. The EDX measurements showed that there were no foreign elements in the grown samples. The HR-XRD measurement has confirmed that the Al xGa 1−xN/GaN/AlN heterostructures samples were epitaxially grown on Si substrate. All the dominant E2 phonon modes were found in Raman spectra results. Lastly, Al xGa 1−xN/GaN/AlN heterostructures based metal–semiconductor–metal (MSM) UV photodetectors were fabricated and the electrical characteristics of the devices were investigated by using current–voltage ( I–V) and photo-conductivity measurements. The devices presented good I–V and photoconductivity characteristics. 相似文献
5.
The ZnMnO thin films were deposited on glass substrates by radio frequency magnetron sputtering method. The properties of ZnMnO thin films were investigated by high-resolution x-ray diffractometer (HRXRD),atomic force microscopy (AFM), UV-Vis spectrometer and room temperature photoluminescence (PL), under the influence of substrate temperature. The substrate temperature was varied from 300, 400 and 500°C. With increasing the substrate temperature, the structure of the films changed from cubic to hexagonal. The cubic ZnMnO thin films grown along [210] direction, while the hexagonal ones grown along [002] direction. The changes in surface morphology provided a proof on the structural transition. Also, decrease and increase of optical band gap is associated with cubic or hexagonal structure of the films. 相似文献
6.
In 0.05Al 0.10Ga 0.85N epilayers and Al 0.10Ga 0.90N epilayers have been grown on bulk GaN single crystals and GaN templates by radio-frequency (RF) molecular-beam epitaxy (MBE). Photoluminescence (PL) spectra at different temperatures ranged from 8 to 300 K were measured for these epilayers. The decreasing rates of PL peak intensity of the In 0.05Al 0.10Ga 0.85N epilayers were smaller than those of the Al 0.10Ga 0.90N epilayers. The fluctuations of emission intensities were not observed in the In 0.05Al 0.10Ga 0.85N epilayers by cathodoluminescence observations at 77 K. Our results indicate that In-related effects exist in InAlGaN quaternary alloys on substrates with low-dislocation densities, however, expect that the localization effect related to In-segregation is weak. 相似文献
7.
We have studied the evolution of threading dislocations (TDs), stress, and cracking of GaN films grown on (111) Si substrates
using a variety of buffer layers including thin AlN, compositionally graded Al
x
Ga 1-x
N (0 ≤ x ≤ 1), and AlN/Al
y
Ga 1-y
N/Al
x
Ga 1-x
N (0 ≤ x ≤ 1, y = 0 and 0.25) multilayer buffers. We find a reduction in TD density in GaN films grown on graded Al
x
Ga 1-x
N buffer layers, in comparison with those grown directly on a thin AlN buffer layer. Threading dislocation bending and annihilation
occurs in the region in the graded Al
x
Ga 1-x
N grown under a compressive stress, which leads to a decrease of TD density in the overgrown GaN films. In addition, growing
a thin AlN/Al
y
Ga 1-y
N bilayer prior to growing the compositionally graded Al
x
Ga 1-x
N buffer layer significantly reduces the initial TD density in the Al
x
Ga 1-x
N buffer layer, which subsequently further reduces the TD density in the overgrown GaN film. In-situ stress measurements reveal
a delayed compressive-to-tensile stress transition for GaN films grown on graded Al
x
Ga 1-x
N buffer layers or multilayer buffers, in comparison to the film grown on a thin AlN buffer layer, which subsequently reduces
the crack densities in the films. 相似文献
8.
High-quality Al xGa 1−xAs layers with aluminum arsenide content x up to 0.34 have been grown in a low pressure metalorganic chemical vapor deposition (MOCVD) system using trimethylgallium
(TMG), trimethylamine alane (TMAA) and arsine. The carbon content in these films depended on growth conditions but was in
general lower than in those obtained with trimethylaluminum (TMA) instead of TMAA in the same reactor under similar conditions.
Unlike TMA grown layers, the TMAA grown Al xGa 1−xAs layers, (grown at much lower temperature—down to 650° C), exhibited room temperature photolu-minescence (PL). Low temperature
(25 K) PL from these films showed sharp bound exciton peaks with a line width of 5.1 meV for Al 0.25Ga 0.75As. A 39 period Al 0.28Ga 0.72As (5.5 nm)/GaAs (8.0 nm) superlattice grown at 650° C showed a strong PL peak at 25 K with a line width of 5.5 meV attesting
to the high quality of these layers. 相似文献
9.
We have studied the influence of indium (In) composition on the structural and optical properties of In x Ga 1−xN/GaN multiple quantum wells (MQWs) with In compositions of more than 25% by means of high-resolution x-ray diffraction (HRXRD),
photoluminescence (PL), and transmission electron microscopy (TEM). With increasing the In composition, structural quality
deterioration is observed from the broadening of the full width athalf maximum of the HRXRD superlattice peak, the broad multiple
emission peaks oflow temperature PL, and the increase of defect density in GaN capping layers and InGaN/GaN MQWs. V-defects,
dislocations, and two types of tetragonal shape defects are observed within the MQW with 33% In composition by high resolution
TEM. In addition, we found that V-defects result in different growth rates of the GaN barriers according to the degree of
the bending of InGaN well layers, which changes the period thickness of the superlattice and might be the source of the multiple
emission peaks observed in the In xGa 1−xN/GaN MQWs with high in compositions. 相似文献
10.
The surface step structure of Ga 1−xIn xAs ySb 1−y grown by organometallic vapor phase epitaxy on GaSb substrates has been studied by atomic force microscopy. Epilayers were
grown at 525°C and 575°C on (001) GaSb substrates misoriented 2° toward (101) or 6° toward (1
1)B. For Ga 0.88In 0.12As 0.1Sb 0.9 grown at 575°C, the surface exhibits step-bunching on both types of substrates. When the composition is increased to Ga 0.86In 0.14As 0.12Sb 0.88, the periodic step structure breaks down and the surface becomes irregular. The deterioration of the step structure is a
consequence of phase separation at the surface of the metastable GaInAsSb epilayer, which leads to the formation of GaAs-
and InSb-rich regions. The photoluminescence (PL) of such layers show significant broadening due to carrier recombination
in the lower energy gap InSb-rich quaternary regions. On the other hand, the surface of GaInAsSb epilayers grown at a lower
temperature of 525°C is vicinal with steps heights of one to two monolayers. The PL FWHM values are considerably smaller for
these layers. This improvement in material quality is related to smaller adatom lifetimes at the lower growth temperature.
The importance of surface kinetics as it influences the step structure and thermodynamically driven phase separation is discussed. 相似文献
11.
Dry thermal oxidation of GaN thin films grown on Al 2O 3 (0001) has been performed at different temperatures. The oxidized samples were investigated through X-ray diffraction (XRD) and atomic force microscope (AFM). For samples oxidized at temperatures from 800 °C to 950 °C, XRD peaks from the (−201), (−402) and (−603) planes of β-Ga 2O 3 were observed, indicating that a β-Ga 2O 3 layer was formed on GaN epitaxially. The epitaxial relationships were determined to be β-Ga 2O 3(−201)||GaN(002) and an in-plane orientation of β-Ga 2O 3[010]||GaN[110]. When the oxidation temperature is increased further to 1000 °C, in addition to the peaks from the (−201), (−402) and (−603) planes, extra peaks corresponding to other planes appeared, indicating that the oxidized layer had deteriorated to polycrystalline Ga 2O 3. 相似文献
12.
400°C alloying of Ge/Cu/Ge films on modestly doped n-GaN results in linear current-voltage ( I- V) behavior over a wide range of relative Ge compositions. X-ray diffraction (XRD) and Auger depth profiling data suggest that
the lowest contact resistivity is due to film compositions near 25 at.% Ge, where the amount of interfacial nonreacted Ge
is low. Ohmic contact is likely established by a heavily doped GaN interfacial region influenced by premetallization reactive
ion etching (RIE) and later low-temperature alloying, which assists in the formation of donorlike complexes possibly involving
Ge Ga or Si Ga. This contact shows exceptionally smooth surface morphology, as revealed by atomic force microscopy (AFM).
[rl](Received ...; accepted ...) 相似文献
13.
The epitaxial growth of Al xGa 1−xN film with high Al content by metalorganic chemical vapor deposition (MOCVD) has been accomplished. The resulting Al content was determined to be 54% by high resolution X-ray diffraction (HRXRD) and Vegard's law. The full width at half maximum (FWHM) of the AlGaN (0002) HRXRD rocking curve was about 597 arcsec. Atomic force microscopy (AFM) image showed a relatively rough surface with grain-like islands, mainly coming from the low surface mobility of adsorbed Al-species. From transmittance measurement, the cut-off wavelength was around 280 nm and Fabry–Perot fringes were clearly visible in the transmission region. Cathodoluminescence (CL) measurement indicated that there existed a uniformity in the growth direction and a non-uniformity in the lateral direction. 相似文献
14.
B xGa 1−xN films were deposited on 6H-SiC (0001) substrates at 1000°C by low pressure MOVPE using diborane, trimethylgallium, and ammonia
as precursors. The presence of boron was detected by Auger scanning microprobe, the shift of the (00.2) x-ray diffraction
peak, and low-temperature photoluminescence. A single-phase B xGa 1−xN alloy with x=1.5% was produced at the gas phase B/Ga ratio of 0.005. Phase separation into wurtzite BGaN and the B-rich
phase occurred for a B/Ga ratio in the 0.01–0.2 range. Only BN was formed for B/Ga >0.2. The B-rich phase was identified as
h-BN with sp 2 bonding based on the results of Fourier transform infrared spectroscopy. As the diborane flow exceeds the threshold concentration,
the growth rate of BGaN decreases sharply, because the growth of GaN is poisoned by the formation of the slow growing BN phase.
The bandedge emission of B xGa 1−xN varies from 3.451 eV for x=0% with FWHM of 39.2 meV to 3.465 eV for x=1.5% with FWHM of 35.1 meV. The narrower FWHM indicates
that the quality of GaN epilayer is improved with a small amount of boron incorporation. The PL linewidths become broader
as more boron is introduced into the solid solution. 相似文献
15.
Thin films of Si-doped Al xGa 1−xN (0.03≤x≤0.58) having smooth surfaces and strong near-band edge cathodoluminescence were deposited at 0.35–0.5 μm/h on on-axis
6H-SiC(0001) substrates at 1100°C using a 0.1 μm AlN buffer layer for electrical isolation. Alloy films having the compositions
of Al 0.08Ga 0.92N and Al 0.48Ga 0.52N exhibited mobilities of 110 and 14 cm 2/V·s at carrier concentrations of 9.6×10 18 and 5.0×10 17 cm −3, respectively. This marked change was due primarily to charge scattering as a result of the increasing Al concentration in
these random alloys. Comparably doped GaN films grown under similar conditions had mobilities between 170 and ∼350 cm 2/V·s. Acceptor doping of Al xGa 1−xN for x≤0.13 was achieved for films deposited at 1100°C. No correlation between the O concentration and p-type electrical
behavior was observed. 相似文献
16.
In this work, a-plane GaN/ r-sapphire templates have been used to grow nonpolar a-plane ZnO films by pulsed laser deposition. The ZnO film growth temperature was varied in the range of 400°C to 600°C, and
the effect of growth temperature on the properties of the ZnO thin films was investigated using x-ray diffraction, atomic
force microscopy, photoluminescence (PL) spectroscopy, and Raman measurements. The results show that the crystal quality,
surface morphology, strain states, and optical properties of a-plane ZnO films are strongly correlated with the deposition temperature. It is found that the crystallinity of the ZnO films
gets better and the surface roughness decreases with increasing growth temperature. At a growth temperature of 600°C, the
a-ZnO films display the best crystal quality with x-ray (11[`2]0) (11\bar{2}0) omega scan full-width at half-maximum values of 0.28° and 0.41° on axis (11[`2]0) (11\bar{2}0) at azimuth 0° and 90°, respectively. Furthermore, the PL spectrum measured at 83 K is dominated by neutral donor-bound excitons
and free-electron-to-bound ( e- A
0) emission, and relatively intense LO-phonon replicas of ( e- A
0) have also been observed in the a-plane ZnO. The dominance of the free exciton and the appearance of its replicas strongly indicate the high quality of the
film. 相似文献
17.
Aluminum gallium nitride-based double heterostructures with two different active layer widths have been grown on GaN templates by metalorganic chemical vapor deposition. Crystalline quality has been investigated using high-resolution x-ray diffraction analysis, and screw, edge, as well as total dislocation densities in the GaN epilayer have been calculated. The dislocation density of GaN has been found to be on the order of 10 8 cm ?2. The nominal Al composition and in-plane strain ε xx for the AlGaN layer grown on the GaN layer have been measured by asymmetric reciprocal-space mapping. Surface properties and cross-sectional views of the samples have been analyzed using atomic force microscopy (AFM) and field-emission scanning electron microscopy (FESEM), respectively. Room-temperature time-resolved photoluminescence and photoluminescence measurements have been performed on Al 0.18Ga 0.82N/Al 0.45Ga 0.55N double heterostructures and the GaN template. The interface recombination velocity ( S) of AlGaN-based double heterostructures has been calculated using carrier decay time measurement, increasing from 8.7 × 10 3 cm/s to 13.4 × 10 3 cm/s with varying active layer thickness. 相似文献
18.
We report the growth and characterization of unintentionally doped GaN on both exact and vicinal (0001) sapphire substrates.
The GaN heteroepitaxial layers are grown by metalorganic chemical vapor deposition on c-plane A1 2O 3 substrates either on-axis or intentionally misoriented 2° toward the a-plane (1120) or 5 or 9° toward the m-plane (10 10). The samples are characterized by 300K photoluminescence, cathodoluminescence, and Hall-effect measurements
as well as by triple-axis x-ray diffractometry to determine the effect of the misorientation on the optical, electrical, and
structural properties of heteroepitaxial undoped GaN. Ten different sample sets are studied. The data reveal enhanced photo-luminescence
properties, increased electron mobility, a reduced n-type background carrier concentration, and a somewhat degraded surface morphology and crystalline quality for the misoriented
samples compared to the on-axis samples. 相似文献
19.
Ga xIn 1-x P layers with x ≈ 0.5 have been grown by atmospheric pressure organometallic vapor phase epitaxy on GaAs substrates with
10 micron wide, [110]-oriented grooves produced photolithographically on the surface. The [110] steps and the misorientation
produced at the edges of the grooves have been found to have important effects on the formation of the Cu-Pt ordered structure
(ordering on {111} planes) in the GaInP layers during growth. In this work, the groove shape is demonstrated to be critically
important. For the optimum groove shape, with a maximum angle to the (001) surface of between 10 and 16°, single domains of
the (-111) and (1-11) variants of the Cu-Pt ordered structure are formed on the two sides of the groove. Shallow (≤0.25 μm
deep) grooves, with maximum angles of <10°, are less effective. Within the large domains on each side of the groove, small
domains of the other variant are observed. The boundary between the two domains is seen to wander laterally by a micron or
more during growth, due to the change in shape of the groove during growth. For deep (1.5 μm) grooves, with maximum angles
to the (001) plane of 35°, only a single variant is formed on each side of the groove. However, the domains are small, dispersed
in a disordered matrix. For substrates with deep grooves on a GaAs substrate misoriented by 9° toward the [-110] direction,
an interesting and useful pattern is produced. One half of the groove is a single domain which shrinks in size as the growth
proceeds. The other half of the groove, where the misorientation is larger, is disordered. Thus, every groove contains large
(>1 μm 2 cross-sectional area and several mm long) regions of highly ordered and completely disordered material separated by no more
than a few microns. This allows a direct determination of the effect of ordering on the bandgap of the material using cathodoluminescence
(CL) spectroscopy. The 10K photoluminescence (PL) consists of three distinct peaks at 1.94, 1.88, and 1.84 eV. High resolution
CL images reveal that the peaks come from different regions of the sample. The high energy peak comes from the disordered
material and the low energy peak comes from the large ordered domains. Electron microprobe measurements of the solid composition
demonstrate that the shift in emission energy is not due to changes in solid composition. This is the first direct verification that ordering causes a reduction in bandgap of any III/V alloy. Decreasing the Ga 0.5In 0.5P growth rate from the normal 2.0 to 0.5 μ/h is found to enhance ordering in layers grown on planar GaAs substrates. Transmission
electron diffraction results show that the domain size also increases significantly. For material grown on exactly (001)-oriented
substrates, a pronounced [001] streaking of the superlattice spots is observed. This is correlated with the presence of a
dense pattern of fine lines lying in the (001) plane in the transmission electron micrographs. The PL of this highly ordered
material consists of a single peak that shifts to higher energy by > 110 meV as the excitation intensity is increased by several
orders of magnitude. 相似文献
20.
The growth of GaN and AlGaN by molecular beam epitaxy (MBE) has been studied using GaN/SiC substrates. The GaN/SiC substrates
consisted of ∼3 μm thick GaN buffer layers grown on 6H-SiC wafers by metalorganic vapor phase epitaxy (MOVPE) at Crée Research,
Inc. The MBE-grown GaN films exhibit excellent structural and optical properties—comparable to the best GaN grown by MOVPE.
Al xGa 1−xN films (x ∼ 0.06-0.08) and Al xGa 1−xN/GaN multi-quantum-well structures which display good optical properties were also grown by MBE on GaN/SiC substrates. 相似文献
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