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1.
GaN-based visible-blind and AlGaN-based solar-blind avalanche photodiodes (APDs) have been grown and fabricated on sapphire substrates. The GaN p-i- n APDs show low dark current with high gain. The AlGaN layers for the Al 0.55Ga 0.45N-based APDs are grown using a newly developed pulsed metalorganic chemical vapor deposition (MOCVD) process, and the material characterization results show excellent material quality. The spectral responsivity of the devices show a bandpass characteristic with cutoffs in the ultraviolet (UV) visible-blind and solar-blind spectrum for GaN- and Al 0.55Ga 0.45N-based APDs, respectively. 相似文献
2.
Electrical activation studies of Al
x
Ga 1−x
N ( x = 0.45 and 0.51) implanted with Si for n-type conductivity have been made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV
with doses ranging from 1 × 10 14 cm −2 to 1 × 10 15 cm −2 at room temperature. The samples were subsequently annealed from 1150°C to 1350°C for 20 min in a nitrogen environment. Nearly
100% electrical activation efficiency was successfully obtained for the Si-implanted Al 0.45Ga 0.55N samples after annealing at 1350°C for doses of 1 × 10 14 cm −2 and 5 × 10 14 cm −2 and at 1200°C for a dose of 1 × 10 15 cm −2, and for the Al 0.51Ga 0.49N implanted with silicon doses of 1 × 10 14 cm −2 and 5 × 10 14 cm −2 after annealing at 1300°C. The highest room-temperature mobility obtained was 61 cm 2/V s and 55 cm 2/V s for the low-dose implanted Al 0.45Ga 0.55N and Al 0.51Ga 0.49N, respectively, after annealing at 1350°C for 20 min. These results show unprecedented activation efficiencies for Al
x
Ga 1−x
N with high Al mole fractions and provide suitable annealing conditions for Al
x
Ga 1−x
N-based device applications. 相似文献
3.
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
4.
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
5.
Dependences of the intensity of cathodoluminescence in multiple Al 0.55Ga 0.45N/Al 0.45Ga 0.55N quantum wells grown by molecular-beam epitaxy on the growth conditions are studied. An increase (by almost two orders of magnitude) in the intensity of the cathodoluminescence peak with an energy of 4.45 eV is observed as the quantum-well layer grows in the conditions of deep depletion with respect to ammonia. In this case, a tendency towards the mode of three-dimensional growth can be inferred from the pattern of diffraction of high-energy electrons; this effect is interpreted using a model of formation of AlGaN quantum dots. 相似文献
6.
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
7.
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
8.
We report the growth of InN by metalorganic chemical vapor deposition on Si(111) substrates. It was found that the sharpest
InN(002) x-ray diffraction peak could be achieved from the sample prepared on a complex buffer layer that consists of a low-temperature
AlN, a graded Al
x
Ga 1−x
N ( x = 1 → 0), and a high-temperature GaN. The resultant mobility of 275 cm 2/V s thus obtained was 75% larger than that of the InN prepared on a single LT-AlN buffer layer only. 相似文献
9.
The influence of Si doping on the photoluminescence (PL) properties of (Al 0.3Ga 0.7) 0.5In 0.5P/Ga 0.5In 0.5P multiple-quantum-wells (MQWs) was studied. For the samples without p-type layers, the PL peak wavelength from (Al 0.3Ga 0.7) 0.5In 0.5P/Ga 0.5In 0.5P MQWs did not vary when Si was doped in MQWs, the PL peak intensity did not change obviously and the PL FWHM broadened. We consider that Si doping results in worse interface quality of (Al 0.3Ga 0.7) 0.5In 0.5P/Ga 0.5In 0.5P MQWs. However, for the full light-emitting diode (LED) structure samples, the PL intensity of MQWs obviously increased when Si was doped in MQWs. The PL intensity from MQWs with Si-doped barriers was about 13 times stronger than that of undoped MQWs. The PL intensity from MQWs with Si-doped barriers and wells was strong as 28 times as that of undoped MQWs. The reasons are discussed. 相似文献
10.
Electrical activation studies of Si-implanted Al
x
Ga 1−x
N with an Al mole fraction of 11% to 51% have been carried out as a function of ion dose and annealing temperature. The Al
x
Ga 1−x
N samples were implanted at room temperature with Si ions at 200 keV in doses ranging from 1 × 10 14 cm −2 to 1 × 10 15 cm −2, and subsequently annealed from 1100°C to 1350°C for 20 min in a nitrogen environment. The maximum electrical activation
efficiencies for the Al
x
Ga 1−x
N samples with an Al mole fraction less than 40% were obtained for samples implanted with the highest Si dose of 1 × 10 15 cm −2. On the other hand, for the Al
x
Ga 1−x
N samples with an Al mole fraction more than 40%, nearly perfect activation efficiencies of 99% and 100% were obtained for
the samples implanted with the lowest Si dose of 1 × 10 14 cm −2. The mobility of the Si-implanted Al
x
Ga 1−x
N samples increased with increasing annealing temperature in spite of the increased number of ionized donors and thus increased
impurity scattering, indicating that a greater amount of lattice damage is being repaired with each successive increase in
annealing temperature. These results provide suitable annealing conditions for Si-implanted Al
x
Ga 1−x
N-based devices with an Al mole fraction from 11% to 51%. 相似文献
11.
We report on fabrication and studies of composite heterostuctures consisting of an Al0.55Ga0.45N/Al0.8Ga0.2N quantum well and surface Al nanoislands, grown by plasma-assisted molecularbeam epitaxy on c-sapphire substrates. The influence of a substrate temperature varied between 320 and 700ºC on the size and density of the deposited Al nanoislands is evaluated. The effect of Al nanoislands on decay kinetics of the quantum well middle-ultraviolet photoluminescence has been investigated by time resolved photoluminescence. The samples with the maximum density of Al nanoislands of 108 cm–2 and lateral dimensions in the range of 100–500 nm demonstrated shortening of the photoluminescence lifetime, induced by interaction of the emitting quantum well and the plasmonic metal particles. 相似文献
12.
Electrical and optical activation studies of lower dose Si-implanted Al xGa 1?xN (x=0.14 and 0.24) have been made systematically as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×10 13 cm ?2 to 1×10 14 cm ?2 at room temperature. The samples were proximity cap annealed from 1,100°C to 1,350°C with a 500-Å-thick AlN cap in a nitrogen environment. Nearly 100% electrical activation efficiency was obtained for Al 0.24Ga 0.76N implanted with a dose of 1 × 10 14 cm ?2 after annealing at an optimum temperature around 1,300°C, whereas for lower dose (≤5×10 13 cm ?2) implanted Al 0.24Ga 0.76N samples, the electrical activation efficiencies continue to increase with anneal temperature up through 1,350°C. Seventy-six percent electrical activation efficiency was obtained for Al 0.14Ga 0.86N implanted with a dose of 1 × 10 14 cm ?2 at an optimum anneal temperature of around 1,250°C. The highest mobilities obtained were 89 cm 2/Vs and 76 cm 2/Vs for the Al 0.14Ga 0.86N and Al 0.24Ga 0.76N, respectively. Consistent with the electrical results, the photoluminescence (PL) intensity of the donor-bound exciton peak increases as the anneal temperature increases from 1,100°C to 1,250°C, indicating an increased implantation damage recovery with anneal temperature. 相似文献
13.
Al 0.26Ga 0.74N/AlN/GaN high-electron-mobility transistor (HEMT) structures with AlN interfacial layers of various thicknesses were grown on 100-mm-diameter sapphire substrates by metalorganic vapor phase epitaxy, and their structural and electrical properties were characterized. A sample with an optimum AlN layer thickness of 1.0 nm showed a highly enhanced Hall mobility ( μHall) of 1770 cm 2/Vs with a low sheet resistance ( ρs) of 365 Ω/sq. (2DEG density ns = 1.0 × 10 13/cm 2) at room temperature compared with those of a sample without the AlN interfacial layer ( μHall = 1287 cm 2/Vs, ρs = 539 Ω/sq., and ns = 0.9 × 10 13/cm 2). Electron transport properties in AlGaN/AlN/GaN structures were theoretically studied, and the calculated results indicated that the insertion of an AlN layer into the AlGaN/GaN heterointerface can significantly enhance the 2DEG mobility due to the reduction of alloy disorder scattering. HEMTs were successfully fabricated and characterized. It was confirmed that AlGaN/AlN/GaN HEMTs with the optimum AlN layer thickness show superior DC properties compared with conventional AlGaN/GaN HEMTs. 相似文献
14.
High quality Si-doped n-Al 0.6Ga 0.4N thin films were grown on sapphire substrates by molecular beam epitaxy (MBE) by interrupted deposition and subsequent in-situ thermal annealing (IDTA). High-resolution X-ray diffraction, scanning electron microscope, atomic force microscope, photoluminescence and Hall-effect measurements were carried out to characterize the structural, electrical and optical properties. The results showed that the full width at half-maximum of the Si-doped Al 0.6Ga 0.4N (0002) was as low as 160 arcsec. The threading dislocation density decreases two orders of magnitude to 6×110 7 cm −2 by using the IDTA technology. The carrier density and mobility reached at 1.1×10 19 cm −3 and 4.8 cm 2/V s, respectively. Si still acted as a shallow donor even for the heavily doped Al 0.6Ga 0.4N. 相似文献
15.
An accurate charge control model to investigate the effect of aluminum composition, strain relaxation, thickness and doping of the Al mGa 1−mN barrier layer on the piezoelectric and spontaneous polarization induced 2-DEG sheet charge density, threshold voltage and output characteristics of partially relaxed Al mGa 1−mN/GaN HEMTs is proposed. The strain relaxation of the barrier imposes an upper limit on the maximum 2-DEG density achievable in high Al content structures and is critical in determining the performance of lattice mismatched Al mGa 1−mN/GaN HEMTs. The model incorporates the effects of field dependent mobility, parasitic source/drain resistance and velocity saturation to evaluate the output characteristics of Al mGa 1−mN/GaN HEMTs. Close proximity with published results confirms the validity of the proposed model. 相似文献
16.
Near ultraviolet light-emitting diodes (LEDs) with quaternary AlInGaN quantum barriers (QBs) are grown by atmospheric pressure metalorganic vapor phase epitaxy. The indium mole fraction of AlInGaN QB could be enhanced as we increased the TMG flow rate. Both the wavelength shift in EL spectra and forward voltage at 20 mA current injection were reduced by using AlInGaN QB. Under 100 mA current injection, the LED output power with Al 0.089In 0.035Ga 0.876N QB can be enhanced by 15.9%, compared to LED with GaN QB. It should be attributed to a reduction of lattice mismatch induced polarization mismatch in the active layer. 相似文献
17.
Quaternary barrier layers for GaN-based high-electron-mobility transistors (HEMT) have recently been a focus of interest because
of the possible lattice-matched growth to GaN. This results in a reduction of strain-related defects, while having the option
of adjusting the bandgap separately. A further benefit of the quaternary approach is the possibility to achieve high polarization
and high carrier mobility simultaneously. This may improve the performance of such devices beyond what is possible with ternary
barrier layers. In this work, we report on growth and characterization of Al
x
In
y
Ga 1−x−y
N barrier layers within the range of 16% to 56% Al, 2% to 45% In, and 20% to 82% Ga deposited on conventional GaN buffer layers
on sapphire. We present an effective way to change the composition of quaternary layers and discuss the influence of tensile
and compressive strain on structural and electrical properties. From high-resolution x-ray diffraction (HRXRD), Rutherford
backscattering spectroscopy (RBS), and wavelength-dispersive x-ray spectroscopy (WDX), we determined the compositions and
strain states of the AlInGaN layers. The bandgaps ( E
g) were obtained by spectroscopic ellipsometry (SE). Hall and van der Pauw measurements on thin heterostructure layers yielded
high mobilities in excess of 1550 cm 2/V s and 5350 cm 2/V s at room temperature and 77 K, respectively. 相似文献
18.
We report the growth of ternary aluminum gallium nitride (AlGaN) layers on AlN/sapphire template/substrates by digitally alloyed
modulated precursor flow epitaxial growth (DA-MPEG), which combined an MPEG AlN sub-layer with a conventional metalorganic
chemical vapor deposition (MOCVD)-grown GaN sub-layer. The overall composition in DA-MPEG Al
x
Ga 1−x
N was controlled by adjustment of the growth time (i.e., the thickness) of the GaN sub-layer. As the GaN sub-layer growth
time increased, the Al composition in AlGaN decreased to 50%, but the surface morphology of the AlGaN layer became rough,
and a three-dimensional structure with islands appeared for the DA-MPEG AlGaN with relatively thick GaN sub-layers, possibly
resulting from the Ga adatom surface migration behavior and/or the strain built up from lattice mismatch between AlN and GaN
sub-layers with increasing GaN sub-layer growth time. Through strain analysis by high-resolution x-ray diffraction, reciprocal
space mapping, and scanning transmission electron microscopy, it was found that there was compositional inhomogeneity in the
DA-MPEG AlGaN with AlN and GaN binary sub-layers for the case of the layer with relatively thick GaN sub-layers. 相似文献
19.
Spontaneous and piezoelectric polarization in hexagonal GaN/AlGaN heterostructures give rise to large built-in electric fields.
The effect of the builtin electric field in GaN/Al xGa 1−xN quantum wells was investigated for x=0.2 to 0.8 by photoluminescence studies. The quantum well structures were grown by
molecular beam epitaxy on (0001) sapphire substrates. Cross-sectional transmission electron microscopy performed on the samples
revealed abrupt interfaces and uniform layer thicknesses. The low temperature (4 K) photoluminescence peaks were progressively
red-shifted due to the quantum confined Stark effect depending on the AlN mole fraction in the barriers and the thickness
of the GaN quantum well. Our results verify the existence of very large built-in electric fields of up to 5 MV/cm in GaN/Al 0.8Ga 0.2N quantum wells. 相似文献
20.
This paper gives the composition dependence of the bandgap energy for highly doped n-type Al xGa 1−xN. We report results of the bowing parameter obtained using a random simulation. Three groups of Al xGa 1−xN semiconductors were considered and which are distinguishable by their non degenerate or degenerate character in the doping density (10 17? ND?10 20 cm −3). A striking feature is the large discrepancy of the bandgap bowing (−2.02? b?2.94 eV), as was demonstrated from our calculations. This suggests that high doping may be a possible cause able to induce the large range of bowing parameters reported for Al xGa 1−xN alloys. 相似文献
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