J. Smoliner

Mechanism of bias-dependent contrast in scanning-capacitance-microscopy images

In this work, the physical processes leading to contrast in scanning capacitance microscopy (SCM) are investigated both experimentally and theoretically. Using a p-type epitaxial doping staircase on silicon, we show that a monotonic dependence of the SCM signal on the doping level is only obtained, if the tip bias is adjusted in a way that the sample is either in accumulation or depletion. In the transition region, the SCM signal is nonmonotonic as a function of doping and depends on the bias. Therefore, any doping concentration can yield a maximum SCM signal size. We also show that this behavior is in agreement with the conventional model of a metal-oxide-semiconductor junction.

Scanning microwave microscopy/spectroscopy on metal-oxide-semiconductor systems

In this paper, an analytical model for capacitance measurements by scanning microwave microscopy (SMM)/scanning microwave spectroscopy is presented. The tip-sample interactions are included by using the physics of metal-oxide-semiconductor junctions and the influence of various experimental parameters, such as the operation frequency, tip bias, tip area, oxide thickness, and sample doping are discussed. For calibrated carrier profiling it is shown that all relevant operation parameters of the SMM can be condensed into a single calibration constant and that the sample doping is obtained by using a simple analytical formula.

Quantitative scanning capacitance spectroscopy

In this work, a setup for quantitative scanning capacitance spectroscopy is introduced, where an ultrahigh precision, calibrated capacitance bridge is used together with a commercially available atomic force microscope (AFM). We show that capacitance data measured with this setup are of comparable quality as data obtained on macroscopic metal oxide semiconductor capacitors. In addition, our setup is sensitive enough to resolve the energy distribution of interface traps with the spatial resolution of an AFM. This is an advantage compared to conventional scanning capacitance microscopes, which have a limited energy resolution and only yield qualitative results due to large modulation voltages.

Depletion charge measurements by tunneling spectroscopy GaAs‐GaAlAs field‐effect transistors

The subband energies on GaAs‐GaAlAs field‐effect transistor samples were measured by tunneling spectroscopy using a structure, where the tunneling process starts from an accumulation layer, and a conventional structure, where the electrons tunnel from a metal electrode into the two‐dimensional electron gas. Self‐consistent calculations were performed to determine the depletion charge from the measured subband energies. Furthermore, the influence of a backgate voltage was investigated both experimentally and theoretically. As far as we know, this is the first direct determination of the depletion charge in GaAs‐GaAlAs field‐effect transistor structures.

Process temperature dependent high frequency capacitance-voltage response of ZrO2/GeO2/germanium capacitors

ZrO2/GeO2 dielectrics are grown on germanium substrates by Atomic Layer Deposition (ALD) at substrate temperatures of 150, 200, and 250 °C, respectively. The impact of the deposition temperature on the electrical and structural properties of MOS capacitors is investigated. A significant influence of the ALD temperature on the high frequency capacitance in inversion can be observed, resulting in a shift of the minority carrier response time from 1.15 to 0.2 μs. Time-of-flight secondary ion mass spectroscopy investigations indicate a distinctive depletion of interfacial GeO at higher ALD temperatures, which give rise to trap levels near the oxide/Ge interface.

Metal-organic chemical vapor deposition and nanoscale characterization of zirconium oxide thin films

Abstract We report on the growth of ZrO2 thin films on silicon wafers by metal-organic chemical vapor deposition from zirconiumtrifluoroacetylacetonate at deposition temperatures between 350 and 550 °C. The evolution of surface roughness of the deposited films is thoroughly investigated. Relative roughness is found to be minimum at a deposition temperature of 450 °C and also essentially independent of film thickness. The attained values of relative roughness are shown to be competitive to advanced deposition methods such as atomic layer deposition. Chemical composition of the films is examined in dependence of deposition temperature and post-deposition annealing procedures. Experimental results indicate that optimum properties in regard to chemical composition are obtained after thermal treatment at 650 °C. The film composition is not significantly altered by annealing at higher temperatures. Also the ambient atmosphere during the annealing process is shown to be of minor influence.

Scanning capacitance microscopy with ZrO2 as dielectric material

In this article, we explore the properties of ZrO2 as dielectric material for scanning capacitance microscopy (SCM). The ZrO2 layers were grown by chemical vapor deposition (CVD) at T=450 °C. The low growth temperature together with the good reproducibility of the CVD process and the high dielectric constant make ZrO2 a very promising material for SCM applications. Compared with SiO2 as dielectric material, much thicker ZrO2 layers can be used resulting in reduced leakage currents and improved signal quality. For SiO2 and ZrO2 layers having the same thickness, the latter yields higher signals and therefore an enhanced sensitivity. Furthermore, ZrO2 was found to be quite insensitive to parasitic charging effects, which often disturb SCM measurements on samples with SiO2 layers.

Ballistic electron emission microscopy on biased GaAs–AlGaAs superlattices

In this work, ballistic electron transport through the lowest miniband of a biased GaAs–AlGaAs superlattice is investigated by ballistic electron emission microscopy (BEEM). In the BEEM spectra the miniband manifests itself as clear peak in the second derivative of the ballistic electron current. Biasing the superlattice results in a shift of the miniband position and the corresponding peak position. It is shown that the measured total transmission of the superlattice is in excellent agreement with the calculated transmission, which makes the superlattice a promising tunable energy filter for studying the energetic distribution of ballistic electrons.

Floating electrometer for scanning tunneling microscope applications in the femtoampere range

In this work, a floating, high precision current–voltage converter, applicable to scanning tunneling microscopy (STM) and ballistic electron emission microscopy (BEEM) measurements, is described. The electrometer circuit presented shows a bias independent output offset, adds low noise, and has low thermal drift. The amplifier is useful for any floating applications where an ultrasmall current has to be measured with high resolution (±20 fA). The circuit is fast enough for typical sampling rates required for BEEM or STM image measurements and can also be used for fA measurements related to ground.

Tip geometry effects in scanning capacitance microscopy on GaAs Schottky and metal-oxide-semiconductor-type junctions

In this work, the influence of the tip geometry in scanning capacitance microscopy is investigated experimentally and theoretically on metal-oxide-semiconductor- (MOS) and Schottky-type junctions on gallium-arsenide (GaAs). Using a two-dimensional model we find that on Schottky-type junctions the electric field around the tip is screened by the surface states and that the essential parameters entering the capacitance versus voltage C(V) characteristics are the doping level and the contact area only. In contrast to that, the electric field from the tip penetrates into the semiconductor on a MOS-type junction, and the tip geometry effects are much larger. C(V) spectra are fitted to the experimental data and allowed a quantitative determination of doping levels, oxide thickness, and contact area without further calibration measurements.