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We examine ZnSnN2, a member of the class of materials contemporarily termed “earth-abundant element semiconductors,” with an emphasis on evaluating its suitability for photovoltaic applications. It is predicted to crystallize in an orthorhombic lattice with an energy gap of 2 eV. Instead, using molecular beam epitaxy to deposit high-purity, single crystal as well as highly textured polycrystalline thin films, only a monoclinic structure is observed experimentally. Far from being detrimental, we demonstrate that the cation sublattice disorder which inhibits the orthorhombic lattice has a profound effect on the energy gap, obviating the need for alloying to match the solar spectrum.

Direct epitaxial growth of single-crystalline germanium (Ge) nanowires at room temperature has been performed through an electrodeposition process on conductive wafers immersed in an aqueous bath. The crystal growth is based on an electrochemical liquid-liquid-solid (ec-LLS) process involving the electroreduction of dissolved GeO2(aq) in water at isolated liquid gallium (Ga) nanodroplet electrodes resting on single-crystalline Ge or Si supports. Ge nanowires were electrodeposited on the wafer scale (>10 cm(2)) using only common glassware and a digital potentiostat. High-resolution electron micrographs and electron diffraction patterns collected from cross sections of individual substrate-nanowire contacts in addition to scanning electron micrographs of the orientation of nanowires across entire films on substrates with different crystalline orientations, supported the notion of epitaxial nanowire growth. Energy dispersive spectroscopic elemental mapping of single nanowires indicated the Ga(l) nanodroplet remains affixed to the tip of the growing nanowire throughout the nanowire electrodeposition process. Current-voltage responses measured across many individual nanowires yielded reproducible resistance values. The presented data cumulatively show epitaxial growth of covalent group IV nanowires is possible from the reduction of a dissolved oxide under purely benchtop conditions.

We have investigated the effects of GaAs substrate misorientation on strain relaxation in In x Ga 1Ϫx As films and multilayers. Our calculations of shear stresses due to misfit strain, resolved on the glide plane in the glide direction, reveal that the ␣ and ␤ 60°slip systems are influenced in a nearly identical fashion, for all substrate misorientation directions. Thus, classical models for nucleation and glide of 60°dislocations predict that a substrate misorientation will not influence the degree of ͗110͘ asymmetry in strain relaxation in lattice-mismatched zincblende semiconductor films. Contrary to these predictions, our experimental results reveal asymmetries in strain relaxation ͑for partially relaxed single layers͒ which favor those dislocations aligned with the offcut axis. These asymmetries depend on the substrate misorientation and growth temperature, and are not easily explained by differences in the intrinsic core properties of ␣ and ␤ dislocations. Furthermore, in fully relaxed multilayers ͑grown at lower temperatures͒, and single layers ͑grown at higher temperatures͒, epilayer tilt which increases the (111)B substrate miscut is observed. In the multilayers, this behavior is found to be correlated with the presence of micron-scale surface facets. We consider possible explanations for these results, including nucleation of partial dislocations, interaction of gliding threading dislocations, and strain relaxation predominated by forward and backward gliding ␣ threading dislocation segments. Together, these results support the conclusion that local surface or interface step morphologies are more important than bulk stress effects in determining misfit dislocation formation in the InGaAs/GaAs system.

Articles you may be interested inCurrent-voltage characteristic and sheet resistances after annealing of femtosecond laser processed sulfur emitters for silicon solar cells Appl. Phys. Lett. 105, 053504 (2014); 10.1063/1.4892474 Deactivation of metastable single-crystal silicon hyperdoped with sulfur J. Appl. Phys. 114, 243514 (2013); 10.1063/1.4854835 Supersaturating silicon with transition metals by ion implantation and pulsed laser melting Electronic and structural properties of femtosecond laser sulfur hyperdoped silicon pn-junctions Appl. Phys. Lett. 103, 061904 (2013); 10.1063/1.4817726 Strong sub-band-gap infrared absorption in silicon supersaturated with sulfurThe authors demonstrate the formation of pn and nn + junctions based on silicon supersaturated with sulfur ͑up to 0.46 at. %͒ using a combination of ion implantation and pulsed laser melting. Silicon wafers were implanted at 200 keV 32 S + to doses ranging from 1 ϫ 10 15 to 1 ϫ 10 16 ions/ cm 2 and subsequently melted and resolidified by using a homogenized excimer laser pulse. Above a threshold laser fluence of ϳ1.4 J / cm 2 , the process produces a single crystal supersaturated alloy, free of extended defects, with a sharp junction between the laser melted layer and the underlying substrate, located near the maximum penetration of the melt front. Hall effect measurements indicate that the laser melted layers are n doped with a free carrier density up to 8 ϫ 10 18 /cm 3 that decreases by one-third upon postirradiation furnace annealing at 550°C. Dark current-voltage measurements performed on these structures show good rectifying behavior. The photovoltaic characteristics of the junctions were enhanced by postirradiation annealing at 550-800°C. These effects are attributed to the evolution of a population of point defects that survive the laser treatment. The influence of ion implantation dose, laser fluence, and annealing temperature on the properties of the junctions is also presented and discussed.