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In this work, we present a scheme for room temperature detection of single subsurface InAs quantum dots buried in GaAs by Atomic Force Microscopy based local photocurrent spectroscopy. The measurements were performed at room temperature and ambient conditions. The AFM was used as a nanopositioning system and the AFM tip was used to create a nano-scale Schottky contact in the vicinity of a QD. The photocurrent spectra clearly showed peaks from quantum dots located in the vicinity of the AFM tip. The spatial resolution of the method was determined to be in between 100 nm and 1000 nm. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, photocurrent images of lithographically processed GaAs/AlAs heterostructures are recorded by an atomic force microscope. It is found that the AFM tip sample contact is strongly dependent on the thickness of the native oxide layer on the sample surface. Therefore, the photocurrents increase if a successively increasing tip sample force is applied, which leads to a gradual penetration of the surface oxide layer. Due to the complex behavior of the photocurrent as a function of tip-bias and tip-force, the contrast in photocurrent images is non-monotonic and can be reversed under appropriate bias and force conditions.

The fabrication of nanostructured dielectrics of high purity produced by electron beam induced deposition (EBID) was investigated. Additionally, the process parameters were optimized towards high deposition rate. Silicon oxide was chosen as exemplary dielectric. The deposition was performed with an electron microscope with a self-designed nozzle system. An organo-silicon precursor was used to deposit silicon oxide. The increase of the oxygen content and the reduction of carbon contaminations of the depositions were preformed by adding molecular oxygen. Patterns of large areas as well as nm-scale arrays were fabricated. To optimize the deposition rate the correlation between beam parameters and deposition rate was studied. It has been shown that this direct-write method allows obtaining arbitrary structures with superior material quality.

In this work, quantitative scanning capacitance spectroscopy studies on bulk GaAs samples and InAs quantum dots are carried out in an ambient atmosphere. The experimental results are described by a simple spherical capacitor model, and the corresponding barrier heights and sample dopings are determined. We further find a strong dependence of the C(V) data on the applied tip force. The barrier height decreases significantly with increasing pressure.

In this work, we present a carrier escape study from InAs/GaAs self assembled QD's by the use of photocurrent measurements. As a function of the applied field, we detect a shift of the exciton ground state transition due to the quantum-confined Stark shift. ?From the measured Stark shift S = 4:3 meV we deduce a exciton dipole moment of p = (4.3 ± 0.2) × 10–29 Cm. The tunneling time, which is directly related to the observed photocurrent linewidth due to τ ∼ ħ/(2Γ), changes by a factor of five in the photocurrent regime. The measured linewidth dependency on the electric field is modelled by a simple 1D WKB approximation for the tunneling process, which shows that the energetic position of the wetting layer is important for the measured tunneling time out of the dot. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this article we report the straggling of long-range implantation damage in silicon in the forefront of a focused ion beam induced amorphization zone. Irradiation was carried out at room temperature at a current density of 0.75 A cm−2 (5×1018 ions/cm2 s) using 50 keV Ga+ ions. A highly sensitive tool for detection, an n-metal–oxide–semiconductor field effect transistor is used to quantify and to characterize the distribution profile of ion beam induced electroactive defects. Scanning the beam over active devices allows the extraction of a three-dimensional profile of defects. In situ monitoring of the drive current and intermitting charge pumping measurements revealed the progressive nature of the damage, the generation of interface states, and the lateral extension of irradiation related defects. Far reaching damage cascades extend at least 300 nm in the beam direction and about 220 nm perpendicular to the beam direction of the substrate and define the region of electrically active defects due to parti...

In this article we explore the application of scanning capacitance microscopy (SCM) for studying focused ion beam (FIB) induced damage in silicon. We qualitatively determine the technologically important beam shape by measuring the SCM image of FIB processed implantation spots and by comparison of topographical and SCM data. Further, we investigate the question how deep impinging ions generate measurable damage below the silicon surface. For this purpose, trenches were manufactured using FIB and analyzed by SCM in cross-sectional geometry.

In this paper we explore the application of scanning capacitance microscopy (SCM) for studying focussed ion beam (FIB) induced damage in silicon. We qualitatively determine the technologically important beam shape by measuring the SCM image of FIB processed implantation spots, and by comparison of topographical and SCM data. Further, we investigate how deep impinging ions generate measurable damage below the silicon surface. For this purpose, trenches were manufactured using FIB and analysed by SCM in cross-sectional geometry.

In this paper we compare macroscopic C-V-measurements with (local) scanning capacitance (SCM) measurements to extract electrical parameters. In future microelectronic CMOS devices, [email protected] dielectrics, primarily as gate oxides, will play an important role. The characterization of their electrical behaviour is one key issue to evaluate their suitability. We deposited zirconium dioxide (ZrO"2) thin films by metal-organic chemical vapor deposition (MOCVD) on (100)-silicon substrates to fabricate metal oxide semiconductor gate stacks. These devices were evaluated by conventional C(V) characterization using a probing station. Additionally, we applied a new C(V)-characterization method, allowing to determine electrical characteristics of nm-thick dielectric films on a nanoscopic scale. This method enabled us to directly compare the nanoscopic and macroscopic measurements. As a result, local and global measurements turned out to be consistent. A comparison of our ZrO"[email protected] layers with thermal SiO"2 films indicate a superior behaviour of MOCVD grown ZrsO"2 film.

Heterosystems of metal/insulator/gold type with titanium oxide and tantalum oxide as internal barriers are studied using internal photoemission (IPE), field induced current transport (current transients after voltage steps) and chemical reaction induced current transport (chemicurrent). IPE investigations over a broad energy range from 0.8 to 4.5 eV allow a determination of the interstitial layers band gap and the maximum height of the internal tunnel barrier. The built-in field of the heterosystem is derived by the evaluation of the slope in the photoyield versus photon energy plot. Current transients recorded after voltage steps allow the determination of the heterosystems time constants which generally have a value of some milli seconds. In titanium oxide systems additional time constants with values of several 100 s appear for bias voltages >0.5 V. These time constants are assigned to slow processes altering the height of the titanium oxide barriers.

Well-defined monoclinic nanostructures of beta- Ga(2)O(3) were grown in a chemical vapor deposition apparatus using metallic gallium and oxygen as sources. Stable growth conditions were deduced for nanorods, nanoribbons, nanowires and cones. The types of nanostructures are determined by the growth temperature. We suppose that the vapor-solid growth mechanism rules the growth of nanoribbons and rods. For the nanowires we observed catalytic gold droplets atop, characteristic for the VLS growth mechanism with an extremely high growth rate of up to 10 microm min(-1). Nanowires grown on Al(2)O(3) substrates showed an excellent tendency to grow epitaxially, mapping the hexagonal symmetry of Al(2)O(3)(0001).

It is shown that surface roughness becomes increasingly important as oxide thicknesses decrease. Silicon-silicon dioxide capacitances with thicknesses of 7 nm, 15 nm, and 50 nm are measured with an atomic force microscope (AFM). The height data thusly obtained is used to create three dimensional simulation structures to reproduce measurement data obtained from leakage current measurements. The leakage currents are simulated using the Fowler-Nordheim (FN) tunnelling current model

There is an increasing interest in cell-based microelectronic biosensors for high-throughput screening of new products from the biotech pipeline. This requires fundamental knowledge of the biocompatibility of the materials used as the growing support for the cells. Using monolayer-forming Caco-2 cells of human origin, the biocompatibility of silicon wafers coated with various metals, dielectrics and semiconductors was assessed. Besides microscopic inspection, proliferation of cells indicating viability as well as brush border enzyme activity indicating differentiation of adherent growing cells were chosen as parameters to estimate biocompatibility. The type of wafer used for deposition of the coating initially influences the biocompatibility of the final product. Whereas p-doped silicon was fully biocompatible, n-doped silicon reduced the proliferation of cells. Among the different coatings, Al and Ti even increased the cell growth as compared to glass. Culturing the cells for 6 days on coated wafers demonstrated that the differentiation of adhering cells on Ti- and ZrO2-coated wafers was comparable to glass, whereas coatings with Si3N4, Au, Al, and ITO reduced differentiation to 15–35%. In the cases of Au and Si3N4 this effect equilibrated with prolonged culturing. These results demonstrate the importance of a careful selection of the materials used for the production of cell-based biosensors.

In our previous work we showed that a reproducible monotonic relation between Scanning Capacitance Microscopy (SCM) signal and the sample doping is obtained under appropriate SCM operating conditions. In this work, we quantitatively determine the two‐dimensional carrier distribution of an n‐type ion‐implanted collector region of an industrial transistor sample. As the structures were large enough so that tip geometry effects could be neglected, the SCM data were converted into a two‐dimensional doping distribution via a simple lookup table, which was generated from a one‐dimensional doping profile measured on a reference wafer. In case the depth distribution of carriers is unknown, we show that the lookup table can also be calculated and a calibration can be carried out using e.g. the substrate doping as reference point.

In this work, an unusual low frequency behavior observed in scanning capacitance microscopy/spectroscopy on GaAs/Al2O3 junctions is investigated. Using a two-dimensional simulation, we show that the frequency behavior of the capacitance—voltage curves can be explained through an increased minority carrier concentration at to the GaAs–Al2O3 interface and tip geometry effects on the nanoscale. An analytic approach to estimate the transition frequency between the low frequency and high frequency regime is also given.

In this work, we systematically investigated the force dependence of conductive atomic force microscopy on n-type Si and n-type GaAs. IV curves were recorded under different tip sample forces and the corresponding Schottky barrier heights were extracted. The force dependent barrier heights of the Si and GaAs samples showed distinct reproducible differences. At low forces, the Schottky barriers decrease with increasing force because the native oxide layer on both the Si and the GaAs sample surface has to be penetrated. At intermediate forces on the GaAs sample, the Schottky barrier showed a large forced dependent increase due to the pressure coefficient of the GaAs band gap. Furthermore, a sudden change in the Schottky barrier increase with tip force was interpreted as the Γ‐X band crossover in GaAs.

In this work, we introduce a two color, low intensity photocurrent feedback method for photocurrent spectroscopy utilizing an atomic force microscope (AFM). In most applications, measurements with weak optical excitations are not feasible with an AFM because the powerful AFM feedback laser severely disturbs the measurements. Therefore, we have developed a feedback system based on the pressure dependent Schottky barrier height at the tip-sample interface. The versatility of the new feedback system is demonstrated by recording high resolution photocurrent spectra on GaAsInAs heterostructures.

The quality of electron-beam deposited, few nanometers thick, SiO2 layers on silicon substrates was investigated by scanning capacitance microscopy and spectroscopy. Rapid thermal annealing had to be applied prior to the capacitance versus voltage [C(V)] measurements to obtain typical metal-oxide-semiconductor behavior, and it was found that the total oxide charge is negative on the deposited oxide layers. Higher annealing temperatures resulted in an overall reduction of the number of oxide charges. This opens up the possibility to use electron-beam deposited SiO2 as a dielectric material in metal-oxide-semiconductor prototyping applications.

In this work, quantitative scanning capacitance spectroscopy was applied to investigate the local dielectric properties of a chemical vapor deposition grown ZrO2 layer on low-doped silicon. Due to self-organization effects during the growth process, the ZrO2 layer shows small, periodic thickness variations on micrometer length scales near the sample edges. The measured capacitance data and derived oxide charge densities show the same periodicity as the thickness variations. The magnitude of the change of the oxide charge density, however, cannot be explained by the small thickness variations and is attributed to a local periodic change of the growth dynamics.

We present cross-sectional atomic-force-microscope measurements of buried self-assembled quantum dots. The used method needs a minimum of time and sample preparation (cleaving and etching) to obtain the dot density, dot distribution, and give an estimate of the dot dimensions. Etching only the cleaved surface of the sample opens up the opportunity to determine the properties of a buried dot layer before or even after device fabrication.