Near-field induced FIR Josephson-detection by x-axis-oriented YBa_{2}Cu_{3}O_{7-d} -films

A novel approach to intrinsic Josephson-detection of far infrared radiation is reported utilizing near-zone field effects at electric contacts on c-axis oriented YBa2Cu3O7- films. While only a bolometric signal was observed focusing the radiation far off the contacts on c-axis normal films, irradiating the edge of contacts yielded an almost wavelength independent fast signal showing the characteristic intensity dependence of Josephson-detection. The signal is attributed to a c-axis parallel component of the electric radiation field being generated in the near-zone field of diffraction at the metallic contact structures

Effect of electron heating and radiation pressure on tunneling across Schottky barrier due to giant near field of FIR radiation

The conductance of tunnel junctions formed by n-GaAs and a semitransparent metal electrode on its surface was shown to be changed by normally incident radiation with frequency below the plasma edge of n-GaAs. A spatial redistribution of the electrons due to the radiation pressure and the corresponding change in the shape of the self-consistent Schottky barrier are observed as a photoconductivity response. The comparison of the measured intensity dependence of the response to the theory has revealed an effective enhancement of the radiation field close to the n-GaAs/Me interface. The ratio Ke of the effective radiation intensity to the incident plain-wave intensity has turned out to be as large as 105. The high local electric field results in strong heating of the degenerate electron gas in the Schottky-barrier region that is mostly apparent as a photo-e.m.f. An analysis of the intensity dependence of the photo-e.m.f. is carried out involving the modification of the Schottky barrier by the ponderomotive force, the electron gas heating in Γ- and L-valleys, as well as the heating of LO phonons. The results confirm the value of Ke and allow to estimate the hot-electron temperature in Γ- and L-valleys

FIR-Detektion mit c-Achsen-orientierten epitaktischen YBCO-Schichten

In granularen und epitaktischen mit einem Kippwinkel auf geeignet geschliffenen Substrate aufgewachsenen YBCO-Schichten wird unterhalb von Tc eine Stromantwort auf FIR-Bestrahlung beobachtet, die der Josephson-Kopplung zwischen einzelnen Körnern oder zwischen CO2-Ebenen zugeschrieben wird. In gekippten Schichten kommt dieses Signal dadurch zustande, daß eine Komponente des Stroms parallel zur c-Achse sein kann. In c-Achsen-orientierten epitaktischen Schichten wurde bisher kein derartiges Signal beobachtet. Hier wird gezeigt, daß dies doch möglich ist, wenn man eine Beugungsstruktur auf die Supraleiterschicht aufbringt, die im Nahfeld eine Komponente des elektrischen Feldvektors senkrecht zur Schichtebene erzeugt

Long-living shallow donor excited states of GaP:Te

Long-living shallow donor excited states in semiconductors existing forseveral miliseconds have been observed. Te-donors in GaP have been ionized by means of phonon assisted tunneling in the electric field of pulsed far-infrared laser radiation. The measurements have been carried out in the temperature range of 20-90 K using radiation of wavelength between 35 and 280 mm and intensities up to 1 MW/cm2. The photocunductive signal caused by ionization in response to the laser pulse shows in addition to a fast component (of the order 100 ns) a second component rising after the exciting pulse has ceased and afterwards decaying exponentially. This decay has a strongly temperature dependent time constant varying from microseconds to several miliseconds. It is shown that this complex temporal structure of the signal is caused by a storage of carriers in the valley-orbit split 1s(E) Te shallow donor state. Furthermore it has been proved by the observation of far-infrared to mid-infrared up-conversion that the final step of recombination is achieved by radiative transitions

Storage of electrons in shallow donor excited states of GaP:Te

Tellurium donors in GaP have been ionized by phonon-assisted tunneling in the electric field of pulsed far-infrared laser radiation. In response to the laser pulse a photoconductive signal has been detected with a fast component that follows in time the laser pulse and a slow component that rises after the irradiation has ceased and finally exponentially decays with a strongly temperature-dependent time constant varying from several microseconds to milliseconds. It is shown that this temporal structure of the signal is due to a storage of carriers in the valley-orbit split 1s(E) shallow donor state. Observation of far-infrared to mid-infrared up-conversion demonstrates that the final step of cascade recombination is achieved by radiative transitions

Nahfeld-Verstaerkung des photoresistiven Effektes in n-GaAs/Al-Schottky-Tunnelkontakten

Die Bestrahlung eines n-GaAs/Metall-Tunnel-Schottky- Kontaktes durch die halbtransparente Metallelektrode mit FIR-Strahlung mit Frequenzen unterhalb der Halbleiter-Plasmafrequenz führt zu einer schnellen Änderung des Tunnelwiderstandes, verursacht durch Strahlungsdruck auf das unipolare Plasma und die Rekonstruktion der selbstkonsistenten Schottky-Potentialbarriere. Dieser Effekt ist unabhängig von der FIR-Frequenz, solange diese kleiner als die Plasmafrequenz ist, und linear mit der Intensität. Es wurde beobachtet, daß mikroskopische Oberflächenstrukturen in der Metallelektrode als beugende Sub-Wellenlängen-Aperturen zu einer stark superlinearen Intensitätsabhängigkeit der Antwort führen. Die charakteristische Intensität am Beginn des nichtlinearen Bereiches und die Stärke der Nichtlinearität sind vom Durchmesser dieser Aperturen abhängig. Es wird gezeigt, daß diese Superlinearität durch Verstärkung der ponderomotiven Kraft im Nahfeldbereich der beugenden Aperturen verursacht wird. Dabei treten Verstärkungsfaktoren von bis zu 105 auf