Shanna Crankshaw

Critical diameter for III-V nanowires grown on lattice-mismatched substrates

The authors report the experimental observation of a critical diameter (CD) of III-V compound semiconductor epitaxial nanowires (NWs) grown on lattice-mismatched substrates using Au-catalyzed vapor-liquid-solid growth. The CD is found to be inversely proportional to the lattice mismatch. NWs with well-aligned orientation are synthesized with catalysts smaller than the CD. Well-aligned InP NWs grown on a Si substrate exhibit a record low photoluminescence linewidth (5.1meV) and a large blueshift (173meV) from the InP band gap energy due to quantization. Well-aligned InAs NWs grown on a Si substrate are also demonstrated.

Atomically sharp catalyst-free wurtzite GaAs∕AlGaAs nanoneedles grown on silicon

We report a catalyst-free, self-assembled growth mode generating single-crystal wurtzite phase ultrasharp GaAs∕AlGaAs nanoneedles on both GaAs and Si substrates via low-temperature metal-organic chemical vapor deposition. The needles exhibit record-narrow tip diameters of 2–4nm wide and sharp 6°–9° taper angles. The length is dependent on growth time and up to 3–4μm nanoneedles are attained. The structures do not exhibit twinning defects, contrary to typical GaAs nanowires grown by vapor-liquid-solid catalyzed growth. AlGaAs layered nanoneedle structures are also demonstrated.

Room temperature slow light in a quantum-well waveguide via coherent population oscillation

We report room temperature demonstration of slow light propagation via coherent population oscillation (CPO) in a GaAs quantum well waveguide. Measurements of the group delay of an amplitude modulated signal resonant with the heavy-hole exciton transition reveal delays as long as 830 ps. The measured bandwidth, which approaches 100 MHz, is related to the lifetime of the photoexcited electron-hole (e-h) plasma as expected for CPO process.

Second-harmonic generation from a single wurtzite GaAs nanoneedle

We demonstrate second harmonic generation from a single GaAs nanoneedle with a wurtzite crystal structure. The optical anisotropy of the polar crystal results in strong nonlinear optical conversion compared to normal zincblende GaAs.

Ultraslow light (<200m∕s) propagation in a semiconductor nanostructure

We report time-domain measurements of ultraslow light propagation in a semiconductor quantum-well structure using coherent population oscillation. Delays greater than 1 ns are achieved for an amplitude-modulated optical beam propagating through a 195-nm-long active region, corresponding to group velocities less than 200m∕s. Delays can be easily varied by adjusting the intensity of the control laser. The bandwidth is suitable to delay sub-GHz modulated optical signals.We report time-domain measurements of ultraslow light propagation in a semiconductor quantum-well structure using coherent population oscillation. Delays greater than 1 ns are achieved for an amplitude-modulated optical beam propagating through a 195-nm-long active region, corresponding to group velocities less than 200m∕s. Delays can be easily varied by adjusting the intensity of the control laser. The bandwidth is suitable to delay sub-GHz modulated optical signals.

Core-shell InGaAs/GaAs quantum well nanoneedles grown on silicon with silicon-transparent emission

In(x)Ga(1-x)As wurtzite nanoneedles are grown without catalysts on silicon substrates with x ranging from zero to 0.15 using low-temperature metalorganic chemical vapor deposition. The nanoneedles assume a 6 degrees - 9 degrees tapered shape, have sharp 2-5 nm tips, are 4 microm in length and 600 nm wide at the base. The micro-photoluminescence peaks exhibit redshifts corresponding to their increased indium incorporation. Core-shell InGaAs/GaAs layered quantum well structures are grown which exhibit quantum confinement of carriers, and emission below the silicon bandgap.

Optical properties of InP nanowires on Si substrates with varied synthesis parameters

We report the effect of synthesis parameters on the physical appearance and optical properties of InP nanowires (NWs) grown on Si substrates by metal-organic chemical vapor deposition. A strong dependence on the group V to III precursor ratio is observed on the NW shape and, consequently, its photoluminescence (PL). Narrow, uniform-diameter NWs are achieved with an optimized V/III ratio. The uniform NWs exhibit PL widths as low as 1.4meV. Their peak wavelength does not vary much with excitation, which is important for NW lasers on Si. These characteristics are attributed to the one-dimensional density of states in uniform-diameter NWs.

GaAs nanoneedles grown on sapphire

Heterogeneous integration of dissimilar single crystals is of intense research interests. Lattice mismatch has been the most challenging bottleneck which limits the growth of sufficient active volume for functional devices. Here, we report self-assembled, catalyst-free, single crystalline GaAs nanoneedles grown on sapphire substrates with 46% lattice mismatch. The GaAs nanoneedles have a 2–3 nm tip, single wurtzite phase, excellent optical quality, and dimensions scalable with growth time. The needles have the same sharp, hexagonal pyramid shape from ∼100 nm (1.5 min growth) to ∼9 μm length (3 h growth).

Time resolved microphotoluminescence studies of single InP nanowires grown by low pressure metal organic chemical vapor deposition

The authors report optical studies of InP nanowires (NWs) grown by metal organic chemical vapor deposition. By means of low temperature microphotoluminescence experiments, the authors determined the optical properties of as-grown NWs. The emission of individual NWs is characterized by small linewidths as low as 2.3meV. Blueshifts of the NW emission energy between 25 and 56meV with respect to bulk InP are related to radial carrier confinement in nanowires with diameters between 15 and 50nm. Time resolved investigations reveal a low surface recombination velocity of 6×102cm∕s and indicate thermally activated nonradiative surface recombination above approximately 20K.The authors report optical studies of InP nanowires (NWs) grown by metal organic chemical vapor deposition. By means of low temperature microphotoluminescence experiments, the authors determined the optical properties of as-grown NWs. The emission of individual NWs is characterized by small linewidths as low as 2.3meV. Blueshifts of the NW emission energy between 25 and 56meV with respect to bulk InP are related to radial carrier confinement in nanowires with diameters between 15 and 50nm. Time resolved investigations reveal a low surface recombination velocity of 6×102cm∕s and indicate thermally activated nonradiative surface recombination above approximately 20K.

Observation of strong second harmonic generation from a single wurtzite GaAs nanoneedle

We demonstrate second harmonic generation from a single GaAs nanoneedle with a wurtzite crystal structure. The optical anisotropy of the polar crystal results in strong nonlinear optical conversion compared to normal zincblende GaAs.