Gas source molecular beam epitaxy of high quality AlGaN on Si and sapphire (original) (raw)
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Gas source molecular beam epitaxy of high quality Al[sub x]Ga[sub 1−x]N (0≤x≤1) on Si(111)
Journal of vacuum science & technology, 2001
Layers of Al x Ga 1Ϫx N, with 0рxр1, were grown on Si͑111͒ substrates by gas source molecular beam epitaxy with ammonia. We show that the initial formation of the SiN -Al interlayer between the Si substrate and the AlN layer, at a growth temperature of 1130-1190 K, results in very rapid transition to two-dimensional growth mode of AlN. The transition is essential for subsequent growth of high quality GaN, Al x Ga 1Ϫx N, and AlGaN/GaN superlattices. The undoped GaN layers have a background electron concentration of (2-3)ϫ10 16 cm Ϫ3 and mobility up to ͑800Ϯ100͒ cm 2 /V s, for film thickness ϳ2 m. The lowest electron concentration in Al x Ga 1Ϫx N, with 0.2ϽxϽ0.6, was ϳ(2-3)ϫ10 16 cm Ϫ3 for 0.5-0.7-m-thick film. Cathodoluminescence and optical reflectance spectroscopy were used to study optical properties of these Al x Ga 1Ϫx N layers. We found that the band gap dependence on composition can be described as E g (x)ϭ3.42ϩ1.21xϩ1.5x 2. p-n junctions have been formed on crack-free layers of GaN with the use of Mg dopant. Light emitting diodes with peak emission wavelength at 3.23 eV have been demonstrated.
High temperature AlN intermediate layer in GaN grown by molecular beam epitaxy
Journal of Crystal Growth, 2000
High-temperature AlN intermediate layers with di!erent thicknesses were deposited during the growth of wurtzite GaN on (0 0 0 1) sapphire substrates by plasma-assisted molecular beam epitaxy. When using a 3.5 nm AlN intermediate layer temperature-dependent Van-der-Pauw Hall measurements revealed a mobility enhancement by a factor of 2.5 at room temperature and by a factor of 32 at 30 K. Transmission electron microscopy con"rmed that the better material quality was due to a reduction of dislocation density by about one order of magnitude. Photoluminescence measurements indicate a decrease of full-width at half-maximum of the main emission peak for GaN samples with AlN intermediate layer.
Growth and Characterization of AlxGa1-xN on GaN/Al2O3
16th International Workshop on Physics of Semiconductor Devices, 2012
AlGaN is a promising material to develop UVLEDs and HEMT devices due to the direct wide-band gap material. In the present investigation, AlxGa 1-xN alloys were grown on c-plane sapphire substrate by MOCVD. Al content x was varied in the composition range 0≤x≤0.6. The thickness and Al composition of the AlGaN was determined by HRXRD. The growth rate decreases on increasing the composition of Al. The critical thickness of pseudomorphic AlGaN layer decreases on increasing the composition. Thick layers resulted in cracks and it is important to grow thick layers with high aluminum content free from crack for deep UV LEDs.
Photoluminescence characteristics of polar and nonpolar AlGaN/GaN superlattices
Applied Physics Letters, 2010
High quality Al 0.2 Ga 0.8 N / GaN superlattices ͑SLs͒ with various ͑GaN͒ well widths ͑1.6 to 6.4 nm͒ have been grown on polar c-plane and nonpolar m-plane freestanding GaN substrates by metal-organic chemical vapor deposition. Atomic force microscopy, high resolution x-ray diffraction, and photoluminescence ͑PL͒ studies of SLs have been carried out to determine and correlate effects of well width and polarization field on the room-temperature PL characteristics. A theoretical model was applied to explain PL energy-dependency on well width and crystalline orientation taking into account internal electric field for polar substrate. Absence of induced-internal electric field in nonpolar SLs was confirmed by stable PL peak energy and stronger PL intensity as a function of excitation power density than polar ones.
physica status solidi (a), 2020
Ammonia and plasma-assisted (PA) molecular beam epitaxy modes are used to grow AlN and AlGaN epitaxial layers on sapphire substrates. It is determined that the increase of thickness of AlN buffer layer grown by ammonia-MBE from 0.32 μm to 1.25 μm results in the narrowing of 101 X-Ray rocking curves whereas no clear effect on 002 X-Ray rocking curve width is observed. It is shown that strong GaN decomposition during growth by ammonia-MBE causes AlGaN surface roughening and compositional inhomogeneity, which leads to deterioration of its lasing properties. AlGaN layers grown by ammonia-MBE at optimized temperature demonstrate stimulated emission (SE) peaked at λ = 330 nm, 323 nm, 303 nm and 297 nm with the SE threshold values of 0.7 MW cm-2 , 1.1 MW cm-2 , 1.4 MW cm-2 and 1.4 MW cm-2 , respectively. In comparison to these, AlGaN layer grown using PA-MBE pulsed modes (migration-enhanced epitaxy, metal-modulated
Growth and Characterization of AlGaN/GaN Superlattices
physica status solidi (a), 2001
A set of AlGaN/GaN superlattices (SLs) with various periods (5-40 nm) and various composition of barriers and buffer layers was grown by MOCVD on sapphire substrates. The aluminum incorporation depending on growth rate was investigated. It was observed that for growth of AlGaN layers with AlN mole fraction above 15-20% the growth rate must be significantly reduced to avoid aluminum incorporation saturation. Structures were studied by X-ray diffraction, Raman scattering, and optical absorption spectroscopy. A significant red-shift of absorption edge was observed for SLs with period of 10-40 nm.
Growth of Crack-Free Thick AlGaN Layer and its Application to GaN-Based Laser Diode
MRS Proceedings, 1999
In the field of group-III nitrides, hetero-epitaxial growth has been one of the most important key technologies. A thick layer of AlGaN alloy with higher AlN molar fraction is difficult to grow on sapphire substrate, because the alloy layer is easily cracked. It is thought that one cause of generating cracks is a large lattice mismatch between an AlGaN and a GaN, when AlGaN is grown on the underlying GaN layer. We have achieved crack-free Al 0.07 Ga 0.93 N layer with the thickness of more than 1µm using underlying Al 0.05 Ga 0.95 N layer. The underlying Al 0.05 Ga 0.95 N layer was grown directly on sapphire by using the lowtemperature-deposited buffer layer (LT-buffer layer). Since a lattice mismatch between the underlying Al 0.05 Ga 0.95 N layer and upper Al 0.07 Ga 0.93 N layer is relatively small, the generation of cracks is thought to be suppressed. This technology is applied to a GaN-based laser diode structure, in which thick n-Al 0.07 Ga 0.93 N cladding layer grown on the Al 0.05 Ga 0.95 N layer, improves optical confinement and single-robe far field pattern in vertical direction.