Enhanced device performance of germanium nanowire junctionless (GeNW-JL) MOSFETs by germanide contact formation with Ar plasma treatment

Nanowire Electronics: From Nanoscale to Macroscale

Semiconductor nanowires have attracted extensive interest as one of the best-defined classes of nanoscale building blocks for the bottom-up assembly of functional electronic and optoelectronic devices over the past two decades. The article provides a comprehensive review of the continuing efforts in exploring semiconductor nanowires for the assembly of functional nanoscale electronics and macroelectronics. Specifically, we start with a brief overview of the synthetic control of various semiconductor nanowires and nanowire heterostructures with precisely controlled physical dimension, chemical composition, heterostructure interface, and electronic properties to define the material foundation for nanowire electronics. We then summarize a series of assembly strategies developed for creating well-ordered nanowire arrays with controlled spatial position, orientation, and density, which are essential for constructing increasingly complex electronic devices and circuits from synthetic semiconductor nanowires. Next, we review the fundamental electronic properties and various single nanowire transistor concepts. Combining the designable electronic properties and controllable assembly approaches, we then discuss a series of nanoscale devices and integrated circuits assembled from nanowire building blocks, as well as a unique design of solution-processable nanowire thin-film transistors for high-performance large-area flexible electronics. Last, we conclude with a brief perspective on the standing challenges and future opportunities.

Ge nanoparticles in SiO2 for near infrared photodetectors with high performance

In this work we prepared films of amorphous germanium nanoparticles embedded in SiO₂ deposited by magnetron sputtering on Si and quartz heated substrates at 300, 400 and 500 °C. Structure, morphology, optical, electrical and photoconduction properties of all films were investigated. The Ge concentration in the depth of the films is strongly dependent on the deposition temperature. In the films deposited at 300 °C, the Ge content is constant in the depth, while films deposited at 500 °C show a significant decrease of Ge content from interface of the film with substrate towards the film free surface. From the absorption curves we obtained the Ge band gap of 1.39 eV for 300 °C deposited films and 1.44 eV for the films deposited at 500 °C. The photocurrents are higher with more than one order of magnitude than the dark ones. The photocurrent spectra present different cutoff wavelengths depending on the deposition temperature, i.e. 1325 nm for 300 °C and 1267 nm for 500 °C. These films present good responsivities of 2.42 AW⁻¹ (52 μW incident power) at 300 °C and 0.69 AW⁻¹ (57 mW) at 500 °C and high internal quantum efficiency of ∼445% for 300 °C and ∼118% for 500 °C.

Weak localization and the approach to metal-insulator transition in single crystalline germanium nanowires

We study the low-temperature electronic transport properties of single germanium nanowires (NWs) with diameters down to 45 nm to investigate the weak localization (WL) behavior and approach to metal-insulator transition (MIT) within them. The NWs (single crystalline) we investigate lie on the metallic side of the MIT with an extrapolated zero temperature conductivity [Formula: see text] in the range 23 to 1790 [Formula: see text] cm)^-1 and show a temperature-dependent conductivity which below 30 K can be described by a 3D WL behavior with Thouless length [Formula: see text] and [Formula: see text]. From the observed value of [Formula: see text] and the value of the critical carrier concentration n _c, it is observed that the approach to MIT can be described by the scaling equation [Formula: see text] with [Formula: see text], which is a value expected for an uncompensated system. The investigation establishes a NW size limit for the applicability of 3D scaling theories.

Enabling Energy Efficiency and Polarity Control in Germanium Nanowire Transistors by Individually Gated Nanojunctions

Germanium is a promising material for future very large scale integration transistors, due to its superior hole mobility. However, germanium-based devices typically suffer from high reverse junction leakage due to the low band-gap energy of 0.66 eV and therefore are characterized by high static power dissipation. In this paper, we experimentally demonstrate a solution to suppress the off-state leakage in germanium nanowire Schottky barrier transistors. Thereto, a device layout with two independent gates is used to induce an additional energy barrier to the channel that blocks the undesired carrier type. In addition, the polarity of the same doping-free device can be dynamically switched between p- and n-type. The shown germanium nanowire approach is able to outperform previous polarity-controllable device concepts on other material systems in terms of threshold voltages and normalized on-currents. The dielectric and Schottky barrier interface properties of the device are analyzed in detail. Finite-element drift-diffusion simulations reveal that both leakage current suppression and polarity control can also be achieved at highly scaled geometries, providing solutions for future energy-efficient systems.

Effective Schottky Barrier Height Lowering of Metal/n-Ge with a TiO2/GeO2 Interlayer Stack

A perfect ohmic contact formation technique for low-resistance source/drain (S/D) contact of germanium (Ge) n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) is developed. A metal-interlayer-semiconductor (M-I-S) structure with an ultrathin TiO₂/GeO₂ interlayer stack is introduced into the contact scheme to alleviate Fermi-level pinning (FLP), and reduce the electron Schottky barrier height (SBH). The TiO₂ interlayer can alleviate FLP by preventing formation of metal-induced gap states (MIGS) with its very low tunneling resistance and series resistance and can provide very small electron energy barrier at the metal/TiO₂ interface. The GeO₂ layer can induce further alleviation of FLP by reducing interface state density (D_it) on Ge which is one of main causes of FLP. Moreover, the proposed TiO₂/GeO₂ stack can minimize interface dipole formation which induces the SBH increase. The M-I-S structure incorporating the TiO₂/GeO₂ interlayer stack achieves a perfect ohmic characteristic, which has proved unattainable with a single interlayer. FLP can be perfectly alleviated, and the SBH of the metal/n-Ge can be tremendously reduced. The proposed structure (Ti/TiO₂/GeO₂/n-Ge) exhibits 0.193 eV of effective electron SBH which achieves 0.36 eV of SBH reduction from that of the Ti/n-Ge structure. The proposed M-I-S structure can be suggested as a promising S/D contact technique for nanoscale Ge n-channel transistors to overcome the large electron SBH problem caused by severe FLP.

Reduction of lasing threshold by protecting gas and the structure dependent visual lasing mode of various CdS microstructures

The lasing behaviours of semiconductor micro/nanostructures were studied in different gaseous surroundings, and the lasing threshold of the nanowire was reduced from 10.5 MW/cm² in air to 9.82 MW/cm², 8.25 MW/cm² and 7.22 MW/cm² in Ar, N₂ and He environment, respectively. It is attributed to the transient polarization of molecular gas. Moreover, the narrow-bandwidth lasing from the junction of a comb-like microstructure is hard to realize compared to that in nanowire and nanobelt due to the absence of good resonance cavities, and the only amplified spontaneous emission was observed by the ICCD dynamic images of the photoluminescence. The PL spectra and ICCD dynamic images, as well as lifetime measurement, prove the occurrence of lasing in nanowires and nanobelts with the pumping power increase, which should originate from the exciton-electron scattering and the formation of EHP, respectively. The whispering-gallery-mode lasing in nanowire and Fabry-Perot-Mode lasing in nanobelt were intuitively demonstrated by the ICCD images. The results provide one route to reduce the lasing threshold by the gas protection.

Regrowth of Ge with different degrees of damage under thermal and athermal treatment

In this report, the recrystallization of pre-damaged Ge samples is extensively investigated under steady-state thermal annealing and ultrafast thermal spike-assisted annealing generated by high-energy ions.