Self-assembling processes involved in the molecular beam epitaxy growth of stacked InAs/InP quantum wires

The growth mechanism of stacked InAs/InP(001) quantum wires (QWRs) is studied by combining an atomic-scale cross-sectional scanning tunnelling microscopy analysis with in situ and in real-time stress measurements along the [110] direction (sensitive to stress relaxation during QWR formation). QWRs in stacked layers grow by a non-Stranski-Krastanov (SK) process which involves the production of extra InAs by strain-enhanced As/P exchange and a strong strain driven mass transport. Despite the different growth mechanism of the QWR between the first and following layers of the stack, the QWRs maintain on average the same shape and composition in all the layers of the stack, revealing the high stability of this QWR configuration.     

Few electron double quantum dots in InAs/InP nanowire heterostructures

We report on fabrication of double quantum dots in catalytically grown InAs/InP nanowire heterostructures. In the few-electron regime, starting with both dots empty, our low-temperature transport measurements reveal a clear shell structure for sequential charging of the larger of the two dots with up to 12 electrons. The resonant current through the double dot is found to depend on the orbital coupling between states of different radial symmetry. The charging energies are well described by a capacitance model if next-neighbor capacitances are taken into account.     

InAs/InP radial nanowire heterostructures as high electron mobility devices

Radial core/shell nanowires (NWs) represent an important class of one-dimensional (1D) systems with substantial potential for exploring fundamental materials electronic and photonic properties. Here, we report the rational design and synthesis of InAs/InP core/shell NW heterostructures with quantum-confined, high-mobility electron carriers. Transmission electron microscopy studies revealed single-crystal InAs cores with epitaxial InP shells 2-3 nm in thickness, and energy-dispersive X-ray spectroscopy analysis further confirmed the composition of the designed heterostructure. Room-temperature electrical measurements on InAs/InP NW field-effect transistors (NWFETs) showed significant improvement in the on-current and transconductance compared to InAs NWFETs fabricated in parallel, with a room-temperature electron mobility, 11,500 cm(2)/Vs, substantially higher than other synthesized 1D nanostructures. In addition, NWFET devices configured with integral high dielectric constant gate oxide and top-gate structure yielded scaled on-currents up to 3.2 mA/microm, which are larger than values reported for other n-channel FETs. The design and realization of high electron mobility InAs/InP NWs extends our toolbox of nanoscale building blocks and opens up opportunities for fundamental and applied studies of quantum coherent transport and high-speed, low-power nanoelectronic circuits.     

Molecular beam epitaxy growth methods of wavelength control for InAs/(In)GaAsN/GaAs heterostructures

We discuss the molecular beam epitaxy (MBE) growth methods of emission wavelength control and property investigations for different types of InAs/(In)GaAsN/GaAs heterostructures containing InGaAsN quantum-size layers: (1) InGaAsN quantum wells deposited by the conventional mode in a GaAs matrix, (2) InAs quantum dots deposited in a GaAsN matrix or covered by an InGaAs(N) layer, and (3) InAs/InGaAsN/GaAsN strain-compensated superlattices with quantum wells and quantum dots. The structures under investigation have demonstrated photoluminescence emission in a wavelength range of ～1.3-1.8?μm at room temperature without essential deterioration of the radiative properties.     

Bismuth surfactant mediated growth of InAs quantum dots by molecular beam epitaxy

This paper explores the significance of using bismuth as a surfactant during the molecular beam epitaxy growth of InAs quantum dots (QDs). The results show that Bi-mediated growth provides a practical solution towards achieving lower density QDs with high optical quality. The InAs QDs grown using Bi as a surfactant exhibit a 50 % lower QD density, narrower QD size distribution, and a doubled photoluminescence peak intensity at 16 K compared to those grown without Bi.     

Mechanisms of layer growth during molecular beam epitaxy of semiconductor films

This paper reviews our present understanding of particular aspects of the surface processes involved in the growth of epitaxial semiconductor films by molecular beam epitaxy. Emphasis is placed on adatom migration and incorporation on GaAs (001) substrates during the growth of GaAs, a comparison with equivalent growth effects on (110) and (111)A oriented substrates, and the influence of mismatch and substrate orientation on growth mode and strain relaxation in the InAs/GaAs system. A brief indication of surface segregation behaviour is also included.     

GaAsN/GaAs and InGaAsN/GaAs heterostructures grown by molecular beam epitaxy

Molecular beam epitaxy was used to fabricate GaAsN/GaAs and InGaAsN/GaAs heterostructures, and the influence of the growth regimes on their characteristics was studied. It is shown that implantation of nitrogen causes a substantial long-wavelength shift of the radiation. The possibility of obtaining 1.4 μm radiation at room temperature was demonstrated using In_0.28Ga_0.72As_0.97N_0.03/GaAs quantum wells. Pis’ma Zh. Tekh. Fiz. 24, 81–87 (December 12, 1998)     

Molecular beam epitaxy growth of free-standing plane-parallel InAs nanoplates

Free-standing nanostructures such as suspended carbon nanotubes, graphene layers, III-V nanorod photonic crystals and three-dimensional structures have recently attracted attention because they could form the basis of devices with unique electronic, optoelectronic and electromechanical characteristics. Here we report the growth by molecular beam epitaxy of free-standing nanoplates of InAs that are close to being atomically plane. The structural and transport properties of these semiconducting nanoplates have been examined with scanning electron microscopy, transmission electron microscopy, X-ray diffraction and low-temperature electron transport measurements. The carrier density of the nanoplates can be reduced to zero by applying a voltage to a nearby gate electrode, creating a new type of suspended quantum well that can be used to explore low-dimensional electron transport. The electronic and optical properties of such systems also make them potentially attractive for photovoltaic and sensing applications.     

Self-assembled growth of GaAs anti quantum dots in InAs matrix by migration enhanced molecular beam epitaxy

Self-assembled GaAs anti quantum dots (AQDs) were grown in an InAs matrix via migration enhanced molecular beam epitaxy. The transmission electron microscopy image showed that the 2D to 3D transition thickness is below 1.5 monolayers (MLs) of GaAs coverage. The average diameter and height of the GaAs AQDs for 1.5 ML GaAs coverage taken from the atomic force microscopy image were approximately 29.0 nm and 1.4 nm, respectively. The density was approximately 6.0 x 10(10) cm(-2). The size of the AQDs was enlarged in the InAs matrix compared with that on the surface. These results indicate that the GaAs AQDs in the InAs matrix under tensile strain can be effectively formed with the assistance of the migration enhanced epitaxy method.     

Manipulation of electron orbitals in hard-wall InAs/InP nanowire quantum dots

We present a novel technique for the manipulation of the energy spectrum of hard-wall InAs/InP nanowire quantum dots. By using two local gate electrodes, we induce a strong transverse electric field in the dot and demonstrate the controlled modification of its electronic orbitals. Our approach allows us to dramatically enhance the single-particle energy spacing between the first two quantum levels in the dot and thus to increment the working temperature of our InAs/InP single-electron transistors. Our devices display a very robust modulation of the conductance even at liquid nitrogen temperature, while allowing an ultimate control of the electron filling down to the last free carrier. Potential further applications of the technique to time-resolved spin manipulation are also discussed.     

Optical properties of rotationally twinned InP nanowire heterostructures

We have developed a technique so that both transmission electron microscopy and microphotoluminescence can be performed on the same semiconductor nanowire over a large range of optical power, thus allowing us to directly correlate structural and optical properties of rotationally twinned zinc blende InP nanowires. We have constructed the energy band diagram of the resulting multiquantum well heterostructure and have performed detailed quantum mechanical calculations of the electron and hole wave functions. The excitation power dependent blue-shift of the photoluminescence can be explained in terms of the predicted staggered band alignment of the rotationally twinned zinc blende/wurzite InP heterostructure and of the concomitant diagonal transitions between localized electron and hole states responsible for radiative recombination. The ability of rotational twinning to introduce a heterostructure in a chemically homogeneous nanowire material and alter in a major way its optical properties opens new possibilities for band-structure engineering.     

Au-catalysed free-standing wurtzite structured InAs nanosheets grown by molecular beam epitaxy

Nano Research - In this study, we report the growth of free-standing InAs nanosheets using Au catalysts in molecular beam epitaxy. Detailed structural characterizations suggest that wurtzite...     

Temperature conditions for GaAs nanowire formation by Au-assisted molecular beam epitaxy

Molecular beam epitaxial growth of GaAs nanowires using Au particles as a catalyst was investigated. Prior to the growth during annealing, Au alloyed with Ga coming from the GaAs substrate, and melted. Phase transitions of the resulting particles were observed in?situ by reflection high-energy electron diffraction (RHEED). The temperature domain in which GaAs nanowire growth is possible was determined. The lower limit of this domain (320?°C) is close to the observed catalyst solidification temperature. Below this temperature, the catalyst is buried by GaAs growth. Above the higher limit (620?°C), the catalyst segregates on the surface with no significant nanowire formation. Inside this domain, the influence of growth temperature on the nanowire morphology and crystalline structure was investigated in detail by scanning electron microscopy and transmission electron microscopy. The correlation of the nanowire morphology with the RHEED patterns observed during the growth was established. Wurtzite GaAs was found to be the dominant crystal structure of the wires.     

Native-oxide-based selective area growth of InP nanowires via metal-organic molecular beam epitaxy mediated by surface diffusion

The growth of InP nanowires on an InP(111) B substrate is reported. The substrate native oxide was not removed from the surface prior to growth. Nanowires were grown at 400 °C from gold catalysts in a selective area manner, without bulk growth. Unlike SiO(2)-based metal-organic molecular beam epitaxy selective area growth, the growth reported here is mediated by surface diffusion with a characteristic diffusion length of 4 μm, about an order of magnitude larger than values for diffusion on bare substrates. A pre-growth heating treatment at 450 °C was found to increase the yield of nanowire nucleation from the gold catalysts.     

Focused ion beam creation and templating of InAs and InAs/InP nanospikes

Ion beam irradiation has been examined as a method for creating nanoscale semiconductor pillar and cone structures, but has the drawback of inaccurate nanostructure placement. We report on a method for creating and templating nanoscale InAs spikes by focused ion beam (FIB) irradiation of both homoepitaxial InAs films and heteroepitaxial InAs on InP substrates. These 'nanospikes' are created as In droplets, formed due to FIB irradiation, act as etch masks for the underlying InAs. By pre-patterning the InAs to influence In droplet movement, nanospike locations on homoepitaxial InAs may be controlled with limited accuracy. Creating nanospikes using an InAs/InP heterostructure provides an additional measure of control over where the spikes form because nanospikes will not form on exposed regions of InP. This effect may be exploited to accurately control nanospike placement by pre-patterning an InAs/InP heterostructure to control the location of the InAs/InP interface. Using this heterostructure templating method it is possible to accurately place nanospikes into regular arrays that may be useful for a variety of applications.     

InAs/GaAs nanostructures grown on patterned Si(001) by molecular beam epitaxy

The potential benefit from the combination of the optoelectronic and electronic functionality of III-V semiconductors with silicon technology is one of the most desired outcomes to date. Here we have systematically investigated the optical properties of InAs quantum structure embedded in GaAs grown on patterned sub-micron and nanosize holes on Si(001). III-V material tends to accumulate in the patterned sub-micron holes and a material depletion region is observed around holes when GaAs/InAs/GaAs is deposited directly on patterned Si(001). By use of a 60?nm SiO(2) layer and patterning sub-micron and nanosize holes through the oxide layer to the substrate, we demonstrate that high optical quality InAs nanostructures, both quantum dots and quantum wells, formed by a two-monolayer InAs layer embedded in GaAs can be epitaxially grown on Si(001). We also report the power-dependent and temperature-dependent photoluminescence spectra of these structures. The results show that hole diameter (sub-micron versus nanosize) has a strong effect on the structural and optical properties of GaAs/InAs/GaAs nanostructures.