Near-infrared detection is widely used for nondestructive and non-contact inspections in various areas, including thermography, environmental and chemical analysis as well as food and medical diagnoses. Common room temperature bolometer-type infrared sensors are based on architectures in the mu m range, limiting miniaturization for future highly integrated 'More than Moore' concepts. In this work, we present a first principle study on a highly scalable and CMOS compatible bolometer-type detector utilizing Ge nanowires as the thermal sensitive element. For this approach, we implemented the Ge nanowires on top of a low thermal conducting and highly absorptive membrane as a near infrared (IR) sensor element. We adopted a freestanding membrane coated with an impedance matched platinum absorber demonstrating wavelength independent absorptivity of 50% in the near to mid IR regime. The electrical characteristics of the device were measured depending on temperature and biasing conditions. A strong dependence of the resistance on the temperature was shown with a maximum temperature coefficient of resistance of -0.07 K-1 at T = 100 K. Heat transport simulations using COMSOL were used to optimize the responsivity and temporal response, which are in good agreement with the experimental results. Further, lock-in measurements were used to benchmark the bolometer device at room temperature with respect to detectivity and noise equivalent power. Finally, we demonstrated that by operating the bolometer with a network of parallel nanowires, both detectivity and noise equivalent power can be effectively improved.

The electrical and optical properties of low-dimensional nanostructures depend critically on size and geometry and may differ distinctly from those of their bulk counterparts. In particular, ultrathin semiconducting layers as well as nanowires have already proven the feasibility to realize and study quantum size effects enabling novel ultrascaled devices. Further, plasmonic metal nanostructures attracted recently a lot of attention because of appealing near-field-mediated enhancement effects. Thus, combining metal and semiconducting constituents in quasi one-dimensional heterostructures will pave the way for ultrascaled systems and high-performance devices with exceptional electrical, optical, and plasmonic functionality. This Letter reports on the sophisticated fabrication and structural properties of axial and radial Al-Ge and Al-Si nanowire heterostructures, synthesized by a thermally induced exchange reaction of single-crystalline Ge-Si core-shell nanowires and Al pads. This enables a self-aligned metallic contact formation to Ge segments beyond lithographic limitations as well as ultrathin semiconducting layers wrapped around monocrystalline Al core nanowires. High-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and μ-Raman measurements proved the composition and perfect crystallinity of these metal-semiconductor nanowire heterostructures. This exemplary selective replacement of Ge by Al represents a general approach for the elaboration of radial and axial metal-semiconductor heterostructures in various Ge-semiconductor heterostructures.

In order to improve the electrical behaviour of metal-insulator-metal capacitors with ZrO2 insulator grown by Atomic Layer Deposition, the influence of the insertion of interfacial Cr layers between Pt electrodes and the zirconia is investigated. An improvement of the α-voltage coefficient of capacitance as low as 567 ppm/V2 is achieved for a single layer of Cr while maintaining a high capacitance density of 10.7 fF/μm2 and a leakage current of less than 1.2 × 10−8 A/cm2 at +1 V. The role of the interface is discussed by means of X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy showing the formation of Zr stabilized chromia oxide phase with a dielectric constant of 16.

The impact of annealing temperature and annealing duration on the interface properties of n-Ge/Y2O3/Pt MOS-capacitors is investigated employing an ultrathin catalytically acting Pt-layer. X-ray photoelectron spectroscopy analysis has been used to verify an enhanced growth of GeO2 and thermally stabilizing yttrium germanate at the n-Ge/Y2O3 interface induced by an oxygen post deposition annealing (PDA). Especially at 500 °C and 550 °C high quality Ge/Y2O3 interfaces have been achieved resulting in very low interface trap density of 7.41*1010 eV−1 cm−2. It is shown that either a short oxygen annealing at higher temperatures (550 °C) or a long time annealing at lower temperatures (450 °C) are appropriate to realize low interface trap density (D it). It turns out that a Pt-assisted PDA in combination with a final PMA are needed to reduce hysteresis width significantly and to bring flat band voltages toward ideal values.

Focused electron beam induced etching (FEBIE) with chlorine as etching agent has been used to geometrically shape and to electrically modify semiconductor nanodevices. Selected sections of monocrystalline nanowires were modified directly without the requirement for a photomask or a resist layer. FEBIE as a subtractive nanofabrication technology allows to locally etch active semiconductor devices made of Si or Ge. In this work, chlorine is used as the etchant gas to thin germanium channel structures fabricated by standard photolithography. For effective material removal a sufficiently high electron influence is essential to avoid the pitfalls of this method. Topography and conductivity of FEBIE-modified structures prior and after the etching process was studied by AFM and by electrical I–V characteristics. The presented work demonstrates the potential of Cl-based FEBIE for device prototyping and electrical trimming of future Ge-based nanodevices.

Metal Oxide Semiconductor capacitors are investigated, employing ALD grown Y2O3 as gate dielectric, and n-type (100) germanium as channel substrate. The effect of post deposition annealing (PDA) in oxygen and forming gas atmosphere using a thin catalytically acting platinum (Pt)-layer on the Y2O3/Ge interface is electrically analyzed for buffered hydrofluoric (BHF) and thermally pre-treated Ge-surfaces.The Pt-assisted PDA ensures even for BHF pre-treated samples very low values for the interface trap density D-it of 1.55 x 10(11) eV(-1) cm(-2) and low leakage current densities J of <7 x 10(-9) A/cm(2) outperforming conventional PDA treatments. The interfacial formation of GeO2 and yttrium germanate after PDA is proven by using X-ray Photoelectron Spectroscopy measurements. (C) 2016 Elsevier B.V. All rights reserved.

In this Letter we report on the exploration of axial metal/semiconductor (Al/Ge) nanowire heterostructures with abrupt interfaces. The formation process is enabled by a thermal induced exchange reaction between the vapor–liquid–solid grown Ge nanowire and Al contact pads due to the substantially different diffusion behavior of Ge in Al and vice versa. Temperature-dependent I–V measurements revealed the metallic properties of the crystalline Al nanowire segments with a maximum current carrying capacity of about 0.8 MA/cm2. Transmission electron microscopy (TEM) characterization has confirmed both the composition and crystalline nature of the pure Al nanowire segments. A very sharp interface between the ⟨111⟩ oriented Ge nanowire and the reacted Al part was observed with a Schottky barrier height of 361 meV. To demonstrate the potential of this approach, a monolithic Al/Ge/Al heterostructure was used to fabricate a novel impact ionization device.

Rhodium Schottky barrier contacts on germanium substrates are investigated in terms of electrical, physical, and chemical properties. The Rh, deposited by electron beam evaporation on a n-type (100)-Ge substrate, has been annealed in N2H2 at different temperatures ranging from 450 degrees C up to 800 degrees C. Rh/Ge Schottky diodes were fabricated to extract the Schottky barrier height, the ideality factor as well as the forward to backward current ratio. By using various analyzing techniques such as Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), and High-resolution Transmission Electron Microscopy (HR-TEM), the formation of polycrystalline Rh-germanide RhxGey phases has been proven. At 500 degrees C germanidation temperature an effective SBH of 0.59 eV is extracted showing a high current ratio of 5 x 10(3) and a remarkable low ideality factor of 1.07. (C) 2015 The Electrochemical Society. All rights reserved.

Photovoltaic nano-devices have largely been relying on charge separation in conventional p-n junctions. Junction formation via doping, however, imposes major challenges in process control. Here, we report on a concept for photovoltaic energy conversion at the nano scale without the need for intentional doping. Our approach relies on charge carrier separation in inhomogeneously strained germanium nanowires (Ge NWs). This concept utilizes the strain-induced gradient in bandgap along tapered NWs. Experimental data confirms the feasibility of strain-induced charge separation in individual vapor-liquid-solid grown Ge NW devices with an internal quantum efficiency of ∼5%. The charge separation mechanism, though, is not inherently limited to a distinct material. Our work establishes a class of photovoltaic nano-devices with its opto-electronic properties engineered by size, shape, and applied strain.

The impact of thermal post deposition annealing in oxygen at different temperatures on the Ge/Y2O3 interface is investigated using metal oxide semiconductor capacitors, where the yttrium oxide was grown by atomic layer deposition from tris(methylcyclopentadienyl)yttrium and H2O precursors on n-type (100)-Ge substrates. By performing in-situ X-ray photoelectron spectroscopy, the growth of GeO during the first cycles of ALD was proven and interface trap densities just below 1 × 1011 eV−1 cm−2 were achieved by oxygen annealing at high temperatures (550 °C–600 °C). The good interface quality is most likely driven by the growth of interfacial GeO2 and thermally stabilizing yttrium germanate.

Using a generalized extraction method, the fixed charge density Nint at the interface between in situ deposited SiN and 5 nm thick AlGaN barrier is evaluated by measurements of threshold voltage Vth of an AlGaN/GaN metal insulator semiconductor high electron mobility transistor as a function of SiN thickness. The thickness of the originally deposited 50 nm thick SiN layer is reduced by dry etching. The extracted Nint is in the order of the AlGaN polarization charge density. The total removal of the in situ SiN cap leads to a complete depletion of the channel region resulting in Vth = +1 V. Fabrication of a gate stack with Al2O3 as a second cap layer, deposited on top of the in situ SiN, is not introducing additional fixed charges at the SiN/Al2O3 interface.

During the last decades, focused electron beam induced deposition (FEBID) has become a successful approach for direct-write fabrication of nanodevices. Such a deposition technique relies on the precursor supply to the sample surface which is typically accomplished by a gas injection system using a tube-shaped injector nozzle. This precursor injection strategy implies a position-dependent concentration gradient on the surface, which affects the geometry and chemistry of the final nanodeposit. Although simulations already proposed the local distribution of nozzle-borne gas molecules impinging on the surface, this isolated step in the FEBID process has never been experimentally measured yet. This work experimentally investigates the local distribution of impinging gas molecules on the sample plane, isolating the direct impingement component from surface diffusion or precursor depletion by deposition. The experimental setup used in this work maps and quantifies the local impinging rate of argon gas over the sample plane. This setup simulates the identical conditions for a precursor molecule during FEBID. Argon gas was locally collected with a sniffer tube, which is directly connected to a residual gas analyzer for quantification. The measured distribution of impinging gas molecules showed a strong position dependence. Indeed, a 300-µm shift of the deposition area to a position further away from the impingement center spot resulted in a 50 % decrease in the precursor impinging rate on the surface area. With the same parameters, the precursor distribution was also simulated by a Monte Carlo software by Friedli and Utke and showed a good correlation between the empirical and the simulated precursor distribution. The results hereby presented underline the importance of controlling the local precursor flux conditions in order to obtain reproducible and comparable deposition results in FEBID.

FIB technologies possess a unique ability to form topographies that are difficult or impossible to generate with binary etching through typical photo-lithography. The ability to arbitrarily vary the spatial dose distribution and therefore the amount of milling opens possibilities for the production of a wide range of functional structures with applications in biology, chemistry, and optics. However in practice, the realization of these goals is made difficult by the angular dependence of the sputtering yield and redeposition effects that vary as the topography evolves. An inverse modeling algorithm that optimizes dose profiles, defined as the superposition of time invariant pixel dose profiles (determined from the beam parameters and pixel dwell times), is presented. The response of the target to a set of pixel dwell times in modeled by numerical continuum simulations utilizing 1st and 2nd order sputtering and redeposition, the resulting surfaces are evaluated with respect to a target topography in an error minimization routine. Two algorithms for the parameterization of pixel dwell times are presented, a direct pixel dwell time method, and an abstracted method that uses a refineable piecewise linear cage function to generate pixel dwell times from a minimal number of parameters. The cage function method demonstrates great flexibility and efficiency as compared to the direct fitting method with performance enhancements exceeding ∼10× as compared to direct fitting for medium to large simulation sets. Furthermore, the refineable nature of the cage function enables solutions to adapt to the desired target function. The optimization algorithm, although working with stationary dose profiles, is demonstrated to be applicable also outside the quasi-static approximation. Experimental data confirms the viability of the solutions for 5×7μm deep lens like structures defined by 90 pixel dwell times.

Y2O3 and L2O3/ZrO2 stacks have been examined in terms of their electrical properties in Ge capacitors. It is discussed that scaling of L2O3/ZrO2 stacks into the sub 1 nm EOT regime can be achieved either by using thin amorphous La2O3 capped by a thin ZrO2 layer or by stabilizing the tetragonal or cubic very high-k phase of ZrO2 induced by diffused La and Ge atoms during a PDA step. Y2O3 shows very good interfacial qualities in terms of a low interface trap density and hysteresis when an annealing in O2 atmosphere is applied. Fowler-Nordheim tunneling is identified as the primary leakage current mechanism at high gate bias whereas for the low bias regime leakage current is primary conducted by direct tunneling through the Y2O3 layer.

Various metal oxides are probed as extrinsic thin tunnel barriers in Semiconductor Insulator Semiconductor solar cells. Namely Al2O3, ZrO2, Y2O3, and La2O3 thin films are in between n-type ZnO:Al (AZO) and p-type Si substrates by means of Atomic Layer Deposition. Low reverse dark current–density as low as 3×10−7 A/cm2, a fill factor up to 71.3%, and open-circuit voltage as high as 527 mV are obtained, achieving conversion efficiency of 8% for the rare earth oxide La2O3. ZrO2 and notably Al2O3 show drawbacks in performance suggesting an adverse reactivity with AZO as also indicated by X-ray Photoelectron Spectroscopy.

The development of smart gas sensor devices for daily life application requires considerable technological efforts related to CMOS integration of gassensitive materials. We are focusing on the heterogeneous integration of ultrathin (50nm) SnO2 layers deposited by spray pyrolysis with CMOS devices. With respect to miniaturization and implementation of the sensing layers on micro-hotplates (μhps) we compared the H2 responses for 100x100μm2 and 5x100μm2 sized sensing films and found a very high response of 42% and 28%, respectively, for 10ppm H2. We performed 2-point and 4-point electrical measurements of SnO2 layers on typical CMOS Al contacts and achieved linear V-I characteristic in the full operating temperature range up to 350¡C in 4-point configuration. We also demonstrate the excellent step coverage of the deposited SnO2 layers on passivated CMOS chips, which is highly important for post-CMOS processing of the sensor films.

Controlling the morphology, electronic properties, and growth direction of nanowires (NWs) is an important aspect regarding their integration into devices on technologically relevant scales. Using the vapor-solid-solid (VSS) approach, with Ni as a catalyst and octachlorotrisilane (Si(3)Cl(8), OCTS) as a precursor, we achieved epitaxial growth of rectangular-shaped Si-NWs, which may have important implications for electronic mobility and light scattering in NW devices. The process parameters were adjusted to form cubic α-NiSi(2) particles which further act as the shaping element leading to prismatic Si-NWs. Along with the uncommon shape, also different crystallographic growth directions, namely, [100] and [110], were observed on the very same sample. The growth orientations were determined by analysis of the NWs' azimuths on the Si (111) substrates as well as by detailed transmission electron microscopy (TEM) and selected area electron diffraction (SAED) investigations.

We present enhancement-mode GaN high electron mobility transistors on Si substrates with ZrO2 gate dielectrics of thicknesses t(ox) between 10 and 24 nm. The oxide interlayers between the InAlN/AlN barrier and gate metal allow raising the device threshold voltage up to + 2.3 V and reduce gate leakage current to less than 100 nA/mm with a high drain current on/off ratio of 4 orders of magnitude. We use a model that explains the observed linear dependence of the threshold voltage on tox and allows determining fixed charges at the oxide/barrier interface. (C) 2012 Elsevier B. V. All rights reserved.

In this Letter we present the electrical and electro-optical characterization of single crystalline germanium nanowires (NWs) under tensile strain conditions. The measurements were performed on vapor-liquid-solid (VLS) grown germanium (Ge) NWs, monolithically integrated into a micromechanical 3-point strain module. Uniaxial stress is applied along the < 111 > growth direction of individual, 100 nm thick Ge NWs while at the same time performing electrical and optical characterization at room temperature. Compared to bulk germanium, an anomalously high and negative-signed piezoresistive coefficient has been found. Spectrally resolved photocurrent characterization on strained NWs gives experimental evidence on the strain-induced modifications of the band structure. Particularly we are revealing a rapid decrease in resistivity and a red-shift in photocurrent spectra under high strain conditions. For a tensile strain of 1.8%, resistivity decreased by a factor of 30, and the photocurrent spectra shifted by 88 meV. Individual stressed NWs are recognized as an ideal platform for the exploration of strain-related electronic and optical effects and may contribute significantly to the realization of novel optoelectronic devices, strain-enhanced field-effect transistors (FETs), or highly sensitive strain gauges.