“…A recent study by Ironside et al demonstrated the planar growth of GaAs on micron-scale stripe-patterned GaAs substrates by MBE, but defect formation was still observed in the coalesced material . Lateral epitaxial overgrowth of the III–V material on patterned substrates has been studied extensively in the past, primarily for GaN, but the studies have rarely focused on large area devices such as solar cells . Because the electrical properties and performance of these large area devices are much more sensitive to crystalline defects, a key aspect of homoepitaxial growth of solar cell devices on patterned substrates is to ensure that no defects are introduced during coalescence.…”
One approach to reducing the cost
of high-efficiency III–V
devices involves adding patterned layers to heteroepitaxial or homoepitaxial
substrates to facilitate substrate removal and reuse. However, few
studies have focused explicitly on high-quality devices grown over
patterned substrates, which is required for any cost saving to be
beneficial. In this work, we demonstrate the growth of high-efficiency
GaAs solar cells on GaAs substrates patterned with an array of nanoscale
SiO
X
mask stripes. We show that reducing
the pattern dimensions to submicron length scales with nanoimprint
lithography enables defect-free coalescence. By varying the growth
conditions, faceting of the epilayer material during overgrowth of
the patterned mask was also controlled. A V/III ratio of 200 during
MOVPE overgrowth produced smooth coalesced epilayers, which is desirable
for the growth of subsequent device layers. Inverted GaAs front homojunction
devices grown on patterned GaAs(001) substrates achieved threading
dislocation densities below 5 × 105 cm–2 and maintained >23% solar cell efficiencies at one sun illumination,
equivalent to control devices grown on unpatterned epi-ready substrates.
“…A recent study by Ironside et al demonstrated the planar growth of GaAs on micron-scale stripe-patterned GaAs substrates by MBE, but defect formation was still observed in the coalesced material . Lateral epitaxial overgrowth of the III–V material on patterned substrates has been studied extensively in the past, primarily for GaN, but the studies have rarely focused on large area devices such as solar cells . Because the electrical properties and performance of these large area devices are much more sensitive to crystalline defects, a key aspect of homoepitaxial growth of solar cell devices on patterned substrates is to ensure that no defects are introduced during coalescence.…”
One approach to reducing the cost
of high-efficiency III–V
devices involves adding patterned layers to heteroepitaxial or homoepitaxial
substrates to facilitate substrate removal and reuse. However, few
studies have focused explicitly on high-quality devices grown over
patterned substrates, which is required for any cost saving to be
beneficial. In this work, we demonstrate the growth of high-efficiency
GaAs solar cells on GaAs substrates patterned with an array of nanoscale
SiO
X
mask stripes. We show that reducing
the pattern dimensions to submicron length scales with nanoimprint
lithography enables defect-free coalescence. By varying the growth
conditions, faceting of the epilayer material during overgrowth of
the patterned mask was also controlled. A V/III ratio of 200 during
MOVPE overgrowth produced smooth coalesced epilayers, which is desirable
for the growth of subsequent device layers. Inverted GaAs front homojunction
devices grown on patterned GaAs(001) substrates achieved threading
dislocation densities below 5 × 105 cm–2 and maintained >23% solar cell efficiencies at one sun illumination,
equivalent to control devices grown on unpatterned epi-ready substrates.
“…4a and Supplementary Fig. 9 ), it seems likely that dislocations will result from coalescence above larger masks 9 , 17 , especially if elongated in one direction. Fig.…”
Section: Resultsmentioning
confidence: 99%
“…A common strategy involves the use of a thick mask layer with openings in the shape of long parallel strips. As the epilayer grows through the mask openings, threading dislocation densities are reduced due to a dislocation trapping effect; as growth extends laterally, growth fronts merge over the mask 7 – 12 , 17 , 18 . This process can result in a high crystal quality epilayer although elongated, hemicylindrical voids 7 – 12 may remain at locations where the growth fronts meet.…”
Epitaxial growth is a fundamental step required to create devices for the semiconductor industry, enabling different materials to be combined in layers with precise control of strain and defect structure. Patterning the growth substrate with a mask before performing epitaxial growth offers additional degrees of freedom to engineer the structure and hence function of the semiconductor device. Here, we demonstrate that conditions exist where such epitaxial lateral overgrowth can produce complex, three-dimensional structures that incorporate cavities of deterministic size. We grow germanium on silicon substrates patterned with a dielectric mask and show that fully-enclosed cavities can be created through an unexpected self-assembly process that is controlled by surface diffusion and surface energy minimization. The result is confined cavities enclosed by single crystalline Ge, with size and position tunable through the initial mask pattern. We present a model to account for the observed cavity symmetry, pinch-off and subsequent evolution, reflecting the dominant role of surface energy. Since dielectric mask patterning and epitaxial growth are compatible with conventional device processing steps, we suggest that this mechanism provides a strategy for developing electronic and photonic functionalities.
“…[41][42][43] In optoelectronics, materials are modified to ensure high-quality coalescence of crystal layers on dielectric materials, which will then be used for high-performance optoelectronic devices. 44 To process wastewater generated from offshore oil and gas fields, Liu et al discussed the use of fiber beds with a fiber condensation mechanism, which is composed of hydrophilic and hydrophobic fibers with a specific proportion and configuration that can separate both dispersed and emulsified oils. 45 Amid et al fabricated polycarbonate ultrafiltration mixed-matrix membranes that incorporated modified halloysite nanotubes and graphene oxide nanosheets, which were used for the separation of olive oil/water emulsions.…”
The coalescence of oil droplets in membrane filtration has not been studied extensively despite its practical importance. The oil removal, filtering coalescence and settling coalescence of electrospun nanofibrous chlorinated polyvinyl...
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