M. S. Dunaevskiy

Nitride Surface Passivation of GaAs Nanowires: Impact on Surface State Density

Surface nitridation by hydrazine-sulfide solution, which is known to produce surface passivation of GaAs crystals, was applied to GaAs nanowires (NWs). We studied the effect of nitridation on conductivity and microphotoluminescence (μ-PL) of individual GaAs NWs using conductive atomic force microscopy (CAFM) and confocal luminescent microscopy (CLM), respectively. Nitridation is found to produce an essential increase in the NW conductivity and the μ-PL intensity as well evidence of surface passivation. Estimations show that the nitride passivation reduces the surface state density by a factor of 6, which is of the same order as that found for GaAs/AlGaAs nanowires. The effects of the nitride passivation are also stable under atmospheric ambient conditions for six months.

Near field imaging of a semiconductor laser by scanning probe microscopy without a photodetector

We propose an experimental method of near field optical imaging by scanning probe microscopy in which the probe itself serves as an infrared photodetector. The method providing a submicron spatial resolution is based on detection of a shift of the probe resonance related to its heating by absorbed IR radiation. The method does not require an apertured probe and can be realized with a conventional silicon probe used in atomic force microscopy. The method has been employed for visualization of infrared emission from a half-disk semiconductor whispering gallery mode laser.

Analysis of the lateral resolution of electrostatic force gradient microscopy

Signal measured by electrostatic force gradient microscopy (EFGM) is the z-gradient of the electrostatic force acting between the probe of an atomic force microscope (AFM) and the surface under study. A model is presented for calculating the z-gradient of the electrostatic interaction of the AFM probe with local charges in a dielectric layer at the surface. In the EFGM mode, the interaction of charges with only the probe tip apex should be taken into account. In this approach, a simplified expression can be derived for calculating the z-gradient of the electrostatic force. The model makes it possible to estimate the lateral resolution limit for EFGM imaging of individual charges and to simulate experimental EFGM images as a function of the tip-surface distance and the tip radius. The adequacy of the model was confirmed by quantitative simulation of the experimental EFGM images of local charges injected from the AFM probe into a planar array of Si nanocrystals in a thin SiO2 layer on a Si substrate.

Observing visible-range photoluminescence in GaAs nanowires modified by laser irradiation

We study the structural and chemical transformations induced by focused laser beam in GaAs nanowires with an axial zinc-blende/wurtzite (ZB/WZ) heterostructure. The experiments are performed using a combination of transmission electron microscopy, energy-dispersive X-ray spectroscopy, Raman scattering, and photoluminescence spectroscopy. For both the components of heterostructure, laser irradiation under atmospheric air is found to produce a double surface layer which is composed of crystalline arsenic and of amorphous GaOx. The latter compound is responsible for the appearance of a peak at 1.76 eV in photoluminescence spectra of GaAs nanowires. Under an increased laser power density, due to sample heating, evaporation of the surface crystalline arsenic and formation of β-Ga2O3 nanocrystals proceed on the surface of the zinc-blende part of nanowire. The formed nanocrystals reveal a photoluminescence band in a visible range of 1.7–2.4 eV. At the same power density for wurtzite part of the nanowire, total a...

Direct measurement of elastic modulus of InP nanowires with Scanning Probe Microscopy in PeakForce QNM mode

In this manuscript, we present the study of elastic properties of InP nanowires with help of scanning probe microscope in advanced PeakForce Tapping® regime. The measuring method was developed in order to investigate the Youngs modulus of these cone-shaped structures with significant accuracy. The difference in InP elasticity for wurtzite phase and zinc- blende phase was revealed. It was shown that elastic modulus of InP nanowires significantly increases from 60 GPa to more than 100 GPa when diameter of a nanowire is reduced below 50 nm. The core-shell model for InP nanowire was used for the explanation of this effect.

Apertureless scanning microscope probe as a detector of semiconductor laser emission

An operating semiconductor laser has been studied using a scanning probe microscope. A shift of the resonance frequency of probe that is due to its heating by laser radiation has been analyzed. The observed shift is proportional to the absorbed radiation and can be used to measure the laser near field or its output power. A periodical dependence of the measured signal has been observed as a function of distance between the probe and the surface of the laser due to the interference of the outgoing and cantilever-reflected waves. Due to the multiple reflections resulting in the interference, the light absorption by the probe cantilever is greatly enhanced compared with a single pass case. Interaction of infrared emission of a diode laser with different probes has been studied.

GaAs Wurtzite Nanowires for Hybrid Piezoelectric Solar Cells

The properties of the hybrid energy sources “piezoelectric nanogenerator-solar cell” based on GaAs nanowires with the wurtzite crystal structure were investigated. Measurements were performed by the bending of the nanowire by the probe of the atomic force microscope with simultaneous recording of short circuit current in dark and illuminated conditions. We show that a piezoelectric current pulse of ~10 pA arises in the “nanowire-probe” circuit during the deformation of nanowire by the AFM probe. Under laser illumination, the value of the pulse increases by two orders of magnitude as a result of the piezophototronic effect. Deformation of the nanowire boosts the photocurrent by 40% up to 0.5 nA.

Optical and electrical properties of the MoSe2/graphene heterostructures

Optical and electrical properties of MoSe2 monolayer transferred to graphene/SiC substrate are studied by scanning probe microscopy and photoluminescence spectroscopy. By Kelvin probe microscopy it was measured a work function of the MoSe2 monolayer (4.3 eV) and it was revealed the n-type of doping. With the increasing of MoSe2 layers quantity the work function also increases which leads to the reducing of the Schottky barrier height between the SPM probe and the layers. Monolayer graphene quenches photoluminescence of the MoSe2 monolayer while the bilayer graphene does not perturb the photoluminescence.

Spatial mode structure in a half-disk cavity laser

We experimentally and theoretically examined the mode structure of half-disk lasers fabricated by cleaving whispering gallery mode (WGM)-disk lasers. The WGM lasers with a radii R of 50–150 μm emitting near 2.2 μm were fabricated using the GaSb-based quantum well structure [1]. The cleavage usually passes not through the centre of the disk with the deviation δ/R up to 20 % (Fig. 1a). Recently we have demonstrated that in the half-disk lasers the output beam is formed by optical modes located at a distance of 5–20 μm from the disk periphery [2], whereas in the full disk the light propagates along the disk wall, much closer to its edges.

I-V curve hysteresis induced by gate-free charging of GaAs nanowires' surface oxide

The control of nanowire-based device performance requires knowledge about the transport of charge carriers and its limiting factors. We present the experimental and modeled results of a study of electrical properties of GaAs nanowires (NWs), considering their native oxide cover. Measurements of individual vertical NWs were performed by conductive atomic force microscopy (C-AFM). Experimental C-AFM observations with numerical simulations revealed the complex resistive behavior of NWs. A hysteresis of current-voltage characteristics of the p-doped NWs as-grown on substrates with different types of doping was registered. The emergence of hysteresis was explained by the trapping of majority carriers in the surface oxide layer near the reverse-biased barriers under the source-drain current. It was found that the accumulation of charge increases the current for highly doped p+-NWs on n+-substrates, while for moderately doped p-NWs on p+-substrates, charge accumulation decreases the current due to blocking of th...