Semibulk InGaN: A novel approach for thick, single phase, epitaxial InGaN layers grown by MOVPE (original) (raw)
Related papers
Acta Materialia, 2013
We report a comparison of the morphological, structural and optical properties of both InGaN single-layer and multilayered structures, the latter consisting of periodic thin GaN interlayers inserted during InGaN growth. It is shown that such a structure suppresses the In concentration fluctuations and corresponding different states of strain relaxation with depth, both detrimental to solar cell applications. Measurements performed by X-ray diffraction, cathodoluminescence and photoluminescence demonstrate that this multilayer growth is a promising approach to increase both the InGaN layer total thickness and In content in InGaN epilayers. As an example, single-phase 120 nm thick InGaN with 14.3% In content is obtained and found to possess high structural quality.
Journal of Crystal Growth, 2014
Thick InGaN alloys with high In content are essential for emerging InGaN photovoltaic applications. By applying a compositionally graded structure, various thicknesses of InGaN layers were grown using metal organic chemical vapor deposition. We could obtain pseudomorphic and highly strained layer even upto 100 nm of InGaN film as confirmed by X-ray reciprocal space mapping and Raman spectra. To probe the validity of those InGaN layers for solar cell applications, optical transmittance measurements were carried out and absorption properties were compared.
Structural, electrical and optical characterization of InGaN layers grown by MOVPE
Chinese Physics B, 2009
We present a study on n-type ternary InGaN layers grown by atmospheric pressure metalorganic vapour phase epitaxy (MOVPE) on GaN template/(0001) sapphire substrate. An investigation of the different growth conditions on n-type InxGa 1−x N (x = 0.06 − 0.135) alloys was done for a series of five samples. The structural, electrical and optical properties were characterized by high resolution x-ray diffraction (HRXRD), Hall effect and photoluminescence (PL). Experimental results showed that different growth conditions, namely substrate rotation (SR) and change of total H 2 flow (THF), strongly affect the properties of InGaN layers. This case can be clearly observed from the analytical results. When the SR speed decreased, the HRXRD scan peak of the samples shifted along a higher angle. Therefore, increasing the SR speed changed important structural properties of InGaN alloys such as peak broadening, values of strain, lattice parameters and defects including tilt, twist and dislocation density. From PL results it is observed that the growth conditions can be changed to control the emission wavelength and it is possible to shift the emission wavelength towards the green. Hall effect measurement has shown that the resistivity of the samples changes dramatically when THF changes.
First Demonstration Of Direct Growth Of Planar High-ln-Composition InGaN Layers on Si
Applied Physics Express Apex, 2013
We report on the direct growth of high-In-composition InGaN layers on Si(111) by plasma-assisted molecular beam epitaxy without any buffer layers. In a narrow window of growth conditions, laterally extended, micrometer-sized planar areas are formed together with trenches and holes. Detailed structural and optical analyses reveal that the planar areas comprise the InGaN layer with high and uniform In composition, while the trenches and holes are associated with pure GaN and low-In-composition InGaN. Photoluminescence at low temperature is observed from the high-In-composition InGaN layer, which forms an ohmic contact with a p-Si substrate. # 2013 The Japan Society of Applied Physics S emiconductor devices require planar base layers and InGaN is the material of choice for the widest range of applications, particularly when grown on Si, opening the door for the integration of III-N technology with Si technology, as well as advanced device designs. With the established energy band gap of InN of 0.7 eV, InGaN alloys have attracted immense interest because they cover band gaps ranging from 0.7 to 3.4 eV, hence, wavelengths from the ultraviolet to the near-infrared. 1) This is the basis for the unmatched range of applications in optoelectronics devices. 2) While optoelectronic devices such as light-emitting diodes, lasers, and photodetectors operating in the ultraviolet and visible spectral region are well developed, novel applications now become possible with the spectral region extended into the near-infrared. 3-6) Among these are lightemitting devices and detectors operating in the important 1.3 and 1.55 m telecom wavelength bands and, most recently discussed, multijunction and intermediate-band solar cells with the ideal band gaps tuned for maximized absorption of solar radiation. All these applications require planar InGaN layers of sufficient thickness with high In composition of 40-50%. These are most difficult to grow epitaxially due to phase separation, InN decomposition, and In desorption, which can only be avoided at low growth temperatures. On top of these difficulties, though without clear reasons stated, the direct growth of InGaN on Si is regarded impossible. Therefore, AlN or GaN, or combined buffer layers are always employed. 10,11) These buffer layers, however, introduce an energy barrier to electrically isolate the InGaN layer from the Si substrate. Hence, advanced device designs cannot be realized, as most prominently discussed, InGaN/Si tandem solar cells where, due to unique band alignment, an ohmic p-Si/n-In 0:46 Ga 0:54 N contact was theoretically predicted. We have grown high-In-composition InGaN layers directly on Si(111) substrates by plasma-assisted molecular beam epitaxy (PA-MBE) without any buffer layers. In a very narrow window of growth conditions, laterally extended, micrometer-sized planar areas are formed together with trenches and holes. Such a morphology is well-known from the growth of pure GaN on Si involving nucleation, lateral growth, coalescence, and two-dimensional film growth. Scanning electron microscopy (SEM), high-resolution Xray diffraction (XRD), along with cathodoluminescence (CL) imaging at room temperature reveal that the planar areas comprise the InGaN layer with high and uniform In composition, while the trenches and holes are associated with pure GaN plus low-In-composition InGaN. Photoluminescence (PL) is observed from the high-In-composition InGaN layer at low temperature. Current-voltage (I-V ) measurements reveal an ohmic p-Si/n-InGaN contact.
Structural and optical properties of InGaN/GaN layers close to the critical layer thickness
Applied Physics Letters, 2002
Structural and optical properties of InGaN / GaN multiple quantum wells ͑MQWs͒ grown on nano-air-bridged GaN template by metal organic chemical vapor deposition were investigated. The InGaN / GaN MQWs on nano-air-bridged GaN demonstrate much better surface morphology, revealing low defect density ϳ4 ϫ 10 8 cm −2 with step flow features measured by atomic force microscopy. The photoluminescence measurement shows one magnitude higher in intensity from less defective InGaN MQWs compared to that of the control InGaN MQWs. The improvement in photoluminescence of the InGaN MQWs is benefited from the reduction of threading dislocation density in the InGaN / GaN active layers and GaN template, revealed from cross-sectional transmission electron microscopy. High resolution x-ray diffraction analysis results show higher indium mole fraction in the MQWs when grown on nano-air-bridged GaN template, due to the strain relaxation in the nano-air-bridged GaN template. This higher indium incorporation is consistent with the redshift of the photoluminescence peak.
First Demonstration of Direct Growth of Planar High-In-Composition InGaN Layers on Si
Applied Physics Express, 2013
We report on the direct growth of high-In-composition InGaN layers on Si(111) by plasma-assisted molecular beam epitaxy without any buffer layers. In a narrow window of growth conditions, laterally extended, micrometer-sized planar areas are formed together with trenches and holes. Detailed structural and optical analyses reveal that the planar areas comprise the InGaN layer with high and uniform In composition, while the trenches and holes are associated with pure GaN and low-In-composition InGaN. Photoluminescence at low temperature is observed from the high-In-composition InGaN layer, which forms an ohmic contact with a p-Si substrate. # 2013 The Japan Society of Applied Physics S emiconductor devices require planar base layers and InGaN is the material of choice for the widest range of applications, particularly when grown on Si, opening the door for the integration of III-N technology with Si technology, as well as advanced device designs. With the established energy band gap of InN of 0.7 eV, InGaN alloys have attracted immense interest because they cover band gaps ranging from 0.7 to 3.4 eV, hence, wavelengths from the ultraviolet to the near-infrared. 1) This is the basis for the unmatched range of applications in optoelectronics devices. 2) While optoelectronic devices such as light-emitting diodes, lasers, and photodetectors operating in the ultraviolet and visible spectral region are well developed, novel applications now become possible with the spectral region extended into the near-infrared. 3-6) Among these are lightemitting devices and detectors operating in the important 1.3 and 1.55 m telecom wavelength bands and, most recently discussed, multijunction and intermediate-band solar cells with the ideal band gaps tuned for maximized absorption of solar radiation. All these applications require planar InGaN layers of sufficient thickness with high In composition of 40-50%. These are most difficult to grow epitaxially due to phase separation, InN decomposition, and In desorption, which can only be avoided at low growth temperatures. On top of these difficulties, though without clear reasons stated, the direct growth of InGaN on Si is regarded impossible. Therefore, AlN or GaN, or combined buffer layers are always employed. 10,11) These buffer layers, however, introduce an energy barrier to electrically isolate the InGaN layer from the Si substrate. Hence, advanced device designs cannot be realized, as most prominently discussed, InGaN/Si tandem solar cells where, due to unique band alignment, an ohmic p-Si/n-In 0:46 Ga 0:54 N contact was theoretically predicted. We have grown high-In-composition InGaN layers directly on Si(111) substrates by plasma-assisted molecular beam epitaxy (PA-MBE) without any buffer layers. In a very narrow window of growth conditions, laterally extended, micrometer-sized planar areas are formed together with trenches and holes. Such a morphology is well-known from the growth of pure GaN on Si involving nucleation, lateral growth, coalescence, and two-dimensional film growth. Scanning electron microscopy (SEM), high-resolution Xray diffraction (XRD), along with cathodoluminescence (CL) imaging at room temperature reveal that the planar areas comprise the InGaN layer with high and uniform In composition, while the trenches and holes are associated with pure GaN plus low-In-composition InGaN. Photoluminescence (PL) is observed from the high-In-composition InGaN layer at low temperature. Current-voltage (I-V ) measurements reveal an ohmic p-Si/n-InGaN contact.
physica status solidi (a), 2015
Nanoselective area growth (NSAG) of thick InGaN nanopyramid and nanostripe arrays was demonstrated using metal organic chemical vapor deposition. SiO 2 nanopattern masks were fabricated using a simple and industry friendly e-beam lithography process. One hundred nanometer thick InGaN is grown with perfect selectivity over patterned GaN templates. InGaN nanostructures are homogenously pyramidal in shape, are mostly free from intrinsic material defects, and show six smooth semipolar facets. Catholuminescence emission peaks from the nanostructures are stronger than those from planar InGaN, which is due to improvement in crystal quality. The emission peaks from nanostructures are considerably redshifted from 397 to 425 nm, confirming increase in In incorporation in the nanostructures from 7 to 9% indium in InGaN. The ability to incorporate more indium depending on the geometry of the patterns and to grow selectively defect-free thick InGaN nanostructures via a simple patterning process offers a new route to develop monolithic InGaN-based high efficiency solar cells.
Design, growth, fabrication and characterization of high-band gap InGaN/GaN solar cells
2006
One of the key requirements to achieve solar conversion efficiencies greater than 50% is a photovoltaic device with a band gap of 2.4 eV or greater. InxGa1-xN is one of a few alloys that can meet this key requirement. InGaN with indium compositions varying from 0 to 40% is grown by both metal-organic, chemical-vapor deposition (MOCVD) and molecular beam epitaxy (MBE), and studied for suitability in photovoltaic applications.