Gas source molecular beam epitaxy of high quality Al[sub x]Ga[sub 1−x]N (0≤x≤1) on Si(111) (original) (raw)
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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.
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.
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.
Gas source molecular beam epitaxy of high quality AlGaN on Si and sapphire
MRS Proceedings, 2000
ABSTRACTWe report the results of epitaxial growth experiments on AlxGa1−xN (0≤ x ≤ 1) on Si(111) and sapphire substrates aimed at understanding the origin and elimination of cracking. We describe growth procedures resulting in thick layers of AlxGa1−xN, grown by gas source molecular beam epitaxy with ammonia, that are free of cracks. In GaN layers with the thickness of ∼2.5 µm, we find the background electron concentration of (1-2)×1016 cm−3 and mobility of (800±100) cm2/Vs. In AlxGa1−xN (0.2 < x < 0.6) with the film thickness of 0.5-0.7 µm the electron concentration of (2-3)×1016 cm−3 is obtained. Low background concentrations in GaN allow for formation of p-n junctions by doping with Mg. Light emitting diodes with the peak emission at 380 nm have been demonstrated.
Applied Physics Letters, 2004
The effects of the isoelectronic Al doping of epitaxial GaN films grown by metalorganic chemical vapor deposition on a ͑0001͒ Al 2 O 3 single crystal substrate were investigated. It was found that the threading screw and edge dislocation densities of the GaN film decreased to less than half of that of the undoped GaN film up to Al doping concentration of 0.45%. The in-plane and out-of-plane strains were simultaneously reduced with the decrease in dislocation density as a result of the solution hardening effect. Accordingly, the electron mobility of the 0.45% Al-doped GaN film (524 cm 2 /Vs) was greatly improved compared to that of the undoped GaN film (178 cm 2 /Vs). However, the threading dislocation densities and strains were increased at a 0.64% Al concentration, and the electron mobility decreased accordingly. Therefore, the improvement in the electron mobility by Al doping up to 0.45% is the result of a decrease in the threading dislocation density and not a decrease in the number of point defects ͑Ga-site vacancy͒ as suggested earlier ͓Lee et al., Appl. Phys. Lett. 83, 917 ͑2003͔͒. Al x Ga 1Ϫx N/GaN heterostructure field effect transistors have recently attracted a great deal of interest for their applications in areas such as high power, high temperature, and microwave devices, due to their high electric breakdown field, large band gap, high thermal stability and high saturation-electron-drift velocity. 1,2 However, it is still difficult to grow high-quality epitaxial GaN films because a high density of treading dislocations and deep levels are inevitably generated as a result of the large lattice mismatch ͑16%͒ and the difference in the thermal expansion coefficients between the GaN thin film and the sapphire (Al 2 O 3 ) substrate. Lee et al. reported that isoelectronic doping of a small concentration of Al ͑Ͻ1%͒ in GaN was effective in improving the device performance. 3 They attributed these improvements to the reduction in the number of point defects ͓Gasite vacancies (V Ga ) and V Ga complexes͔. 4 However, it is difficult to understand why Al doping reduced the V Ga during the film growth because V Ga , as a point defect, is not the V Ga until the GaN crystal is formed and the incorporation of Al atoms does not have any specific reason to fill out the V Ga during the film growth. Furthermore, how the strain state of the GaN films changes with increasing Al concentration has not been explored.
Journal of Applied Physics, 2010
The influence of the growth method on the surface potential and thus on the sheet carrier concentration of GaN capped Al x Ga 1−x N / GaN heterostructures was evaluated. Nominally undoped low pressure metal-organic vapor-phase ͑MOVPE͒ and plasma-assisted molecular beam epitaxial ͑PA-MBE͒ grown structures with an Al-content between 12% and 30% yield carrier concentrations from 3.6ϫ 10 12 to 1.2ϫ 10 13 cm −2 . A difference of the concentrations for a fixed Al-content was found between the different epitaxial techniques. This result indicates unambiguously different surface potentials determined quantitatively from the carrier concentration, and is verified in addition by the results of photoreflectance spectroscopy. The GaN surface potentials of MOVPE and PA-MBE grown samples amounts to ͑0.26Ϯ 0.04͒ and ͑0.61Ϯ 0.10͒ eV irrespective of the Al-content of the barrier layer. After device fabrication, we find that due to the identical surface potential defined by the Ni Schottky gate, the threshold voltage for a given Al-content is the same for samples grown with different techniques. Thus, the interplay between epitaxy and process technology defines the threshold voltage.
Applied Physics Letters, 2011
GaN based heterostructures have recently gained increased interest due to their applications for high electron mobility transistors. In this letter AlInN/AlN/GaN heterojunctions grown by metal-organic chemical-vapor deposition with different AlN thicknesses have been investigated by surface photovoltage spectroscopy. The density of the two-dimensional electron gas ͑2DEG͒ forming at the interface has been measured by Hall effect. A band gap shift has been detected and its dependence on the 2DEG electron density at the AlN/GaN interface has been analyzed on the basis of the Moss-Burstein and renormalization effects.
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.