Nano Selective Area Growth Research Articles

Selective Area Growth of Cubic Gallium Nitride in Nanoscopic Silicon Dioxide Masks

Herein, the possibilities of nanoselective area growth (NSAG) of cubic gallium nitride on 3C‐SiC/Si (001) pseudo substrates are studied. Growth is masked by SiO2 patterned with hole arrays and groove structures. Nanosphere lithography and block‐copolymer lithography are employed to pattern holes with diameters of 130 and 17 nm, respectively. Electron beam lithography is used to pattern grooves. Patterns are transferred into SiO2 and 3C‐SiC by reactive ion etching with CHF3/Ar and SF6 chemistry, correspondingly. It is possible to demonstrate phase pure nanoselective nucleation of c‐GaN on <001> and <111> facets of 3C‐SiC. Phase pure nucleation of cubic gallium nitride is confirmed by transmission electron microscopy measurements on the nanoscopic scale. A hexagonal fraction of 17.6% is achieved on the macroscopic scale measured by high‐resolution X‐ray diffraction (HRXRD), employing V‐shaped grooves on 4° miscut substrates. Furthermore, the possibility of coalescence after NSAG is demonstrated with the dominant cubic phase.

Nanopyramid-based absorber to boost the efficiency of InGaN solar cells

InGaN nano-structures, grown using nano selective area growth, have been shown to exhibit high crystalline quality, even for high In content InGaN alloy, and reduced polarization charge effect. They are thus very attractive for the realization of high efficiency solar cells. Compared to planar InGaN absorbers, nanopyramid-based absorbers are shown to relax the usual challenging constraint on the doping of the p-GaN layer, which would be needed to overcome the polarization-induced electric field. NP-based solar cells maintain the same performance with ten times lower p-GaN doping. Furthermore, the SiO2 mask used for selective area growth of the nanopyramids is shown to help trap light into the nanopyramids, leading to increased optical absorption and thus efficiency. Last, InGaN nanopyramid absorber-based solar cells can allow for a higher InGaN residual donor concentration than that of the planar InGaN solar cells. Overall, an optimized In0.3Ga0.7N nanopyramid-based solar cell can lead to an efficiency twice than that of a planar InGaN-based solar cells with standard p- and n-GaN doping level. As a proof of concept, an In0.09Ga0.91N nanopyramid-based solar cell has been fabricated and is shown to have larger short circuit photocurrent and open circuit voltage than a state of the art In0.08Ga0.92N-based planar solar cell.

Nanoselective area growth of defect-free thick indium-rich InGaN nanostructures on sacrificial ZnO templates

Nanoselective area growth (NSAG) by metal organic vapor phase epitaxy of high-quality InGaN nanopyramids on GaN-coated ZnO/c-sapphire is reported. Nanopyramids grown on epitaxial low-temperature GaN-on-ZnO are uniform and appear to be single crystalline, as well as free of dislocations and V-pits. They are also indium-rich (with homogeneous 22% indium incorporation) and relatively thick (100 nm). These properties make them comparable to nanostructures grown on GaN and AlN/Si templates, in terms of crystallinity, quality, morphology, chemical composition and thickness. Moreover, the ability to selectively etch away the ZnO allows for the potential lift-off and transfer of the InGaN/GaN nanopyramids onto alternative substrates, e.g. cheaper and/or flexible. This technology offers an attractive alternative to NSAG on AlN/Si as a platform for the fabrication of high quality, thick and indium-rich InGaN monocrystals suitable for cheap, flexible and tunable light-emitting diodes.

Mask effect in nano-selective- area-growth by MOCVD on thickness enhancement, indium incorporation, and emission of InGaN nanostructures on AlN-buffered Si(111) substrates

In this paper, we studied the effect of temperature and mask margin size on optical emission and growth rate enhancement (GRE) of InGaN grown by metal organic chemical vapor deposition (MOCVD) and nano-selective-area growth (NSAG) on AlN-buffered Si(111). For all mask geometries and temperatures, NSAG produced 90% single-crystal InGaN nanopyramids with smooth facets, perfect selectivity, and 1.2 times the indium composition enhancement (23% and 33% for 800 °C and 780 °C NSAG, respectively) as found in non-NSAG planar growth at the same conditions. The vapor phase diffusion model was found to be insufficient to predict NSAG GRE, and we propose an explanation combining mechanisms from the vapor phase diffusion with surface migration models. A two-peak emission was noted for all NSAG. The total and relative intensities of the two peaks was found to be strongly dependent upon both temperature and local indium precursor concentration during growth, the latter of which varies based on mask margin size. In NSAG grown at lower temperature and with higher local indium precursor concentration, the bluer of the two peaks was more dominant and the overall emission intensity was higher. InGaN nanopyramids were chemically uniform, ruling out phase separation as origin of the double-peak. We propose an explanation based on the sudden transition from strained to relaxed growth moderated by temperature and local indium precursor concentration.

Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5–8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metal organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.

Single-crystal nanopyramidal BGaN by nanoselective area growth on AlN/Si(111) and GaN templates

We report nano-selective area growth (NSAG) of BGaN by MOCVD on AlN/Si(111) and GaN templates resulting in 150 nm single crystalline nanopyramids. This is in contrast to unmasked or micro-selective area growth, which results in a multi-crystalline structure on both substrates. Various characterization techniques were used to evaluate NSAG as a viable technique to improve BGaN material quality on AlN/Si(111) using results of GaN NSAG and unmasked BGaN growth for comparison. Evaluation of BGaN nanopyramid quality, shape and size uniformity revealed that the growth mechanism is the same on both the templates. Further STEM analysis of BGaN nanopyramids on AlN/Si (111) templates confirmed that these are single-crystalline structures without any dislocations, likely due to single nucleation occurring in the 80 nm mask opening. CL results correspond to boron content between 1.7% and 2.0% in the nanopyramids. We conclude that NSAG is promising for growth of high-quality BGaN nanostructures and complex nano-heterostructures, especially for low-cost silicon substrates.

Nanoselective area growth and characterization of dislocation-free InGaN nanopyramids on AlN buffered Si(111) templates

We report the metal organic chemical vapor deposition growth of dislocation-free 100 nm thick hexagonal InGaN nanopyramid arrays with up to 33% of indium content by nano-selective area growth on patterned AlN/Si (111) substrates. InGaN grown on SiO2 patterned templates exhibit high selectivity. Their single crystal structure is confirmed by scanning transmission electron microscope combined with an energy dispersive X-ray analysis, which also reveals the absence of threading dislocations in the InGaN nanopyramids due to elastic strain relaxation mechanisms. Cathodoluminescence measurements on a single InGaN nanopyramid clearly show an improvement of the optical properties when compared to planar InGaN grown under the same conditions. The good structural, morphological, and optical quality of the InGaN nanostructures grown on AlN/Si indicates that the nano-selective area growth technology is attractive for the realization of site-controlled indium-rich InGaN nanostructure-based devices and can also be transferred to other highly mismatched substrates.

High quality thick InGaN nanostructures grown by nanoselective area growth for new generation photovoltaic devices

Nanoselective area growth (NSAG) of thick InGaN nanopyramid and nanostripe arrays was demonstrated using metal organic chemical vapor deposition. SiO2 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.

Structural and optical properties of nanodots, nanowires, and multi-quantum wells of III-nitride grown by MOVPE nano-selective area growth

Nanodots, nanowires, and semi-polar quantum well structures of GaN-based material have been grown by nano-selective area growth (NSAG). The growth evolution of the nanostructure has been studied. Cross-sectional transmission electron microscopy (TEM) shows that the nanostructures are free of threading dislocations. The growth of AlGaN/GaN layers is uniform and shows sharp interfaces between the AlGaN and GaN epilayers. AlGaN nanodots/nanowires, which are formed at the apexes of the nano-pyramids/nano-ridges, are found to be homogeneous in size and to have a higher aluminum mole fraction than the surrounding material. In contrast, the InGaN/GaN growth shows no quantum dots at the apexes of the nanostructures. We found that the growth facets of different Miller’s indices are formed on the InGaN/GaN nano-ridges. Energy dispersive X-ray spectroscopy (EDX) shows higher indium incorporation at the intersection of the growth facets. Cathodoluminescence measurements show enhanced luminescence intensity from InGaN multi-quantum wells (MQWs) grown on the nanostructure compared to that from InGaN MQWs grown on an unpatterned area.

One Step Nano-Selective Area Growth of Localized InAs/InP Quantum Dots For Single Photon Source Applications

AbstractWe demonstrate the feasibility of a new approach of Nano Selective Area Growth (Nano-SAG) to precisely localize InAs/InP QDs, by low-pressure Metalorganic Vapour Phase Epitaxy (MOVPE). This approach is based on a partial patterning with a dielectric mask containing nano-openings. The two main advantages of MOVPE are: the important diffusion length of the active species and the inhibition of growth on the dielectric mask. We demonstrate the synthesis of localized nanostructures with high structural properties and the precise control of their dimensions at the nanometer scale. This allows in principle the precise control of the tunability of the emission length.

One-step nano-selective area growth (nano-SAG) of localized InAs/InP quantum dots: First step towards single-photon source applications

We demonstrate the feasibility of a new approach based on the nano selective area growth (nano-SAG), which allows the precise spacial localization, in the nanometer scale, of InAs/InP quantum dots (QDs) grown by low-pressure metal organic vapor-phase epitaxy. By using the hydrogen silsesquioxane-negative resist, we partially pattern the substrate in only one step (e-beam lithography) with dielectric masks containing nano-openings. We demonstrate that the one-step nano-SAG technique leads to the formation of site-controlled InAs/InP QDs with good structural properties, and allows the good control of the growth rate and thus of the QD size into the nano-openings.

New approach of Nano-Selective Area Growth (NSAG) for a precise control of GaN nanodots grown by MOVPE

Nanodots arrays of GaN have been successfully grown on GaN template substrates using nano-selective area growth (NSAG). The substrates used in NSAG were partially covered by dielectric masks in which nano-apertures have been patterned by electron-beam nanolithography and reactive ion etching. The growths were performed by low pressure metal organic vapour phase epitaxy (MOVPE) using 100% N 2 as carrier gas. TMGa and NH 3 were used as sources of gallium and nitrogen, respectively. The layers were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Perfect selectivity of GaN on the masked substrate has been obtained. The nanodots grown in the nano-apertures are well shaped and homogenous with smooth surface side walls.