Au Junctions Research Articles

Light-emission mechanism of Si-MOS tunnel junctions.

The light-emission mechanism of Si-MOS (metal-oxide-semiconductor) junctions has been investigated. Si/${\mathrm{SiO}}_{2}$/metal (Al or Au) MOS junctions with extremely smooth interfaces were fabricated by taking advantage of the well-developed Si processing technology. The observed light-emission spectra can be accounted for by the current fluctuation theory of light-emitting tunnel junctions [B. Laks and D. L. Mills, Phys. Rev. B 20, 4962 (1979)]. There are two channels of light emission: the direct emission from the fluctuation of the tunneling current and the indirect emission that arises from the scattering (by surface roughness) of surface-plasmon polaritons generated by the fluctuating tunnel current. The light from the Si/${\mathrm{SiO}}_{2}$/Al junction arises mainly from the direct emission from the fluctuating current. The light from the Si/${\mathrm{SiO}}_{2}$/Au junction contains both the direct and indirect emissions with approximately equal strengths. The direct and indirect emissions have comparable strength in our junctions, because our Si-based junctions are extremely smooth and the indirect emission is much weaker than in the junctions used in earlier studies.

Electronic properties of metal-poly(pyrrole) junctions†

Abstract In recent years there has been a growing interest in the use of molecular organic materials in microelectronic devices, such as polymer diodes, transistors and gas sensors. Conducting polymers form an important class of organic materials that are being investigated as a substitute for conventional inorganic semiconductor materials. Electrodeposited conducting polymers, such as the pyrrole-based family, have some distinct advantages in their ease of microdeposition and in situ doping, 'tunable’ band-gap and high electronic mobility. In this paper we report on the fabrication and properties of novel poly(pyrrole)-tosylate/metal PPy(pTSA)/metal junctions. Thin (∼0-5 μ,m) PPy(pTSA) films were electrochemically deposited onto small gold electrodes on silicon microelectronic substrates. The PPy(pTSA)/Au junction always forms an ohmic junction. Low work function metal contacts (e.g. Cu and Ag) were either physically evaporated onto the poly(pyrrole) or electrochemically deposited to form the junction. Poor reproducibility was observed in both types of junction with about half the devices exhibiting weakly rectifying junctions (ideality factor of about eight). There was no discernible difference in the characteristics of the evaporated and electrodeposited junctions. The electronic characteristics of the junctions were not consistent with conventional Schottky theory; for example, PPy(pTSA)/Ag always showed an ohmic contact. Instead, the poor stability and general behaviour seems consistent with the formation of an MOS junction following reaction at the interface. Our observations suggest that the development of electrodeposited pyrrole-based microelectronic devices is inherently difficult.

Inelastic electron tunneling in aluminum-alumina-gold junctions exposed to thiocyanate ion: sensitive thiocyanate detection

Inelastic electron tunneling spectra are reported for Al-Al 2 O 3 -Au junctions externally doped with KSCN from methanol solution. Spectra of the thiocyanate ion can be observed over a wide range of concentration, 10 -7 -10 -2 M. Because the tunneldiodes are completely fabricated prior to the doping process, and because the doping process is simple and only requires a few minutes, these devices may serve as solid-state chemical sensors. The spectra observed for externally doped junctions are essentially the same as those for junctions doped with KSCN during device fabrication

Observation and explanation of light-emission spectra from statistically rough Cu, Ag, and Au tunnel junctions

A detailed description of the experimentally observed light output from statistically rough ${\mathrm{A}\mathrm{l}\ensuremath{-}\mathrm{A}\mathrm{l}}_{2}$${\mathrm{O}}_{3}$-$M$ ($M=\mathrm{A}\mathrm{g},\mathrm{A}\mathrm{u},\mathrm{C}\mathrm{u}$) tunnel junctions is presented. These data include a comprehensive description of the polarization and angular distribution of the light emitted from ${\mathrm{A}\mathrm{l}\ensuremath{-}\mathrm{A}\mathrm{l}}_{2}$${\mathrm{O}}_{3}$-Au junctions as well as spectra from reverse-biased ${\mathrm{A}\mathrm{l}\ensuremath{-}\mathrm{A}\mathrm{l}}_{2}$${\mathrm{O}}_{3}$-Ag junctions. It is argued, principally on the grounds of an examination of surface-plasmon---polariton (SPP) damping, that the bulk of the output from statistically rough tunnel junctions is due to the fast-SPP mode. The idea of fast-SPP mediation is found, in many respects, to be much more consistent with currently available experimental results than that of slow- (or junction) SPP mediation. Extant theoretical models hold slow-SPP mediation to be the dominant means of visible-regime emission. The view of the emission mechanism presented in this paper suggests that the statistically rough tunnel junction could emit light more efficiently (if the scale of the surface roughness were altered) and that it has potential as a spectroscopic tool.

Light emission from small metal particles and thin metal films excited by tunneling electrons

We have measured the light intensity versus photon energy of six types of electron tunnel junctions and compared the experimental results to the localized plasmon model of Rendell, M\"uhlschlegel, and Scalapino, and to the smooth and slightly roughened junction model of Laks and Mills. The types of junctions used to test the theories were Al-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ junctions completed with a top electrode consisting of either an evaporated metal film of Au or Ag, or evaporated Au or Ag particles that were electrically connected by an evaporated Au or Ag film. The $p\ensuremath{-}s$-polarized light emitted by junctions with Au or Ag particles is consistent with the localized plasmon model. The "$s$"-polarized light of the particle junctions and the essentially unpolarized light of the Au and Ag film junctions may be consistent with the theory of Laks and Mills for slightly roughened junctions.

Optical spectra and angular dependence of the visible light emitted by metal-insulator-metal tunnel junctions

Optical spectra and angular dependence of electromagnetic emission from Al-Al oxide-Ag and Al-Al oxide-Au tunnel junctions are reported. Data from Ag junctions are consistent with the assumption of roughness induced decoupling of surface polaritons, while data from Au junctions suggest that the emission results from direct coupling of current fluctuations in the junction to the external radiation fields.

Photolithographic fabrication of lead alloy Josephson junctions

Techniques for the photolithographic fabrication of thin-film Josephson junctions are presented in detail, including metal liftoff processes, lead alloy composition, and formation of tunneling junction barriers using plasma oxidation in an rf discharge. A comparison with earlier rf plasma oxidation studies on Pb(In) –oxide–Pb junctions shows the tunneling resistance of Pb(In,Au) –oxide–Pb(Au) junctions to be nearly two decades lower for a given oxygen pressure in the rf discharge; this difference was attributed to the use of different alloys and sputtering parameter measurement techniques in the respective studies. Typically, tunneling resistance decreased by only 2% after ten thermal cycles, but decreased at an accelerated rate with subsequent cycling. Room-temperature storage often induced downward resistance changes on the order of 30% per month. Junctions stored at −15°C generally showed little change after a period of three months.

Defect structure and local conduction in YY 2O 3Au junctions

Observations of the surface of YY 2O 3Au junctions have demonstrated the existence of microscopic local defects caused by electrical conduction. The defects are formed initially during the development of junction conductivity on electro-forming, which is accompanied by instabilities of the current. A close correlation between the current instabilities and the emission of electrons from the junction surface has been confirmed. The observations indicate that conduction is restricted to local defects over the junction surface. The estimated resistivity of the conducting material in the local defects is 100 Ω cm or more, which is much higher than previously reported values. In junctions with a thick oxide layer a different type of defect appears, which is characterized by single-hole non-shorting breakdown.

Bistable switching in ZrZrO 2Au junctions

Bistable switching has been observed in ZrZrO 2Au junctions. The resistance ratio is as high as 10 4. Significant physical changes have occurred during forming and subsequent switching of these junctions. The physical changes were observed by optical microscope, scanning electron microscope, and electron microprobe techniques. The temperature changes and profiles were observed by the liquid crystal technique during forming and switching. These studies indicate that in the low resistance state the current is carried by a single filament centered around one of the spots formed while switching from the high resistance state to the low resistance state. A voltage controlled negative resistance was observed for the junction in the low resistance state.