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Register a new userProgress Towards Opto-Electronic Characterization of Indium Phosphide Nanowire Transistors at milli-Kelvin temperatures
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Added by
Laurens Willems van Beveren
Publication date
2013
fields
Physics
and research's language is
English
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In this paper we present our progress towards the opto-electronic characterization of indium phosphide (InP) nanowire transistors at milli-Kelvin (mK) temperatures. First, we have investigated the electronic transport of the InP nanowires by current-voltage (I-V) spectroscopy as a function of temperature from 300 K down to 40 K. Second, we show the successful operation of a red light emitting diode (LED) at liquid-Helium (and base) temperature to be used for opto-electronic device characterization.
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We have measured the electronic heat capacity of thin film nanowires of copper and silver at temperatures 0.1 - 0.3 K; the films were deposited by standard electron-beam evaporation. The specific heat of the Ag films of sub-100 nm thickness agrees with the bulk value and the free-electron estimate, whereas that of similar Cu films exceeds the corresponding reference values by one order of magnitude. The origin of the anomalously high heat capacity of copper films remains unknown for the moment. Based on the low heat capacity and the possibility to devise a tunnel probe thermometer on it, the Ag films form a promising absorber material, e.g., for micro-wave photon calorimetry.
Generation of very low temperatures has been crucially important for applications and fundamental research, as low-temperature quantum coherence enables operation of quantum computers and formation of exotic quantum states, such as superfluidity and superconductivity. One of the major techniques to reach milli-Kelvin temperatures is adiabatic demagnetization refrigeration (ADR). This method uses almost non-interacting magnetic moments of paramagnetic salts where large distances suppress interactions between the magnetic ions. The large spatial separations are facilitated by water molecules, with a drawback of reduced stability of the material. Here, we show that an H$_2$O-free frustrated magnet KBaYb(BO$_3$)$_2$ can be ideal refrigerant for ADR, achieving at least 22,mK upon demagnetization under adiabatic conditions. Compared to conventional refrigerants, KBaYb(BO$_3)_2$ does not degrade even under high temperatures and ultra-high vacuum conditions. Further, its frustrated magnetic network and structural randomness enable cooling to temperatures several times lower than the energy scale of magnetic interactions, which is the main limiting factor for the base temperature of conventional refrigerants.
We compare the electronic characteristics of nanowire field-effect transistors made using single pure wurtzite and pure zincblende InAs nanowires with nominally identical diameter. We compare the transfer characteristics and field-effect mobility versus temperature for these devices to better understand how differences in InAs phase govern the electronic properties of nanowire transistors.
We determine the thermal conductance of thin niobium (Nb) wires on a silica substrate in the temperature range of 0.1 - 0.6 K using electron thermometry based on normal metal-insulator-superconductor tunnel junctions. We find that at 0.6 K, the thermal conductance of Nb is two orders of magnitude lower than that of Al in the superconducting state, and two orders of magnitude below the Wiedemann-Franz conductance calculated with the normal state resistance of the wire. The measured thermal conductance exceeds the prediction of the Bardeen-Cooper-Schrieffer theory, and demonstrates a power law dependence on temperature as $T^{4.5}$, instead of an exponential one. At the same time, we monitor the temperature profile of the substrate along the Nb wire to observe possible overheating of the phonon bath. We show that Nb can be successfully used for thermal insulation in a nanoscale circuit while simultaneously providing an electrical connection.
The performance of low temperature detectors utilizing thermal effects is determined by their energy relaxation properties. Usually, heat transport experiments in mesoscopic structures are carried out in the steady-state, where temperature gradients do not change in time. Here, we present an experimental study of dynamic thermal relaxation in a mesoscopic system -- thin metallic film. We find that the thermal relaxation of hot electrons in copper and silver films is characterized by several time constants, and that the annealing of the films changes them. In most cases, two time constants are observed, and we can model the system by introducing an additional thermal reservoir coupled to the film electrons. We determine the specific heat of this reservoir and its coupling to the electrons. The experiments point at the importance of grain structure on the thermal relaxation of electrons in metallic films.
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