E. Gornik

Polarization-sensitive surface plasmon Schottky detectors

A polarization detector based on the excitation of surface plasmon polaritons on the periodically corrugated metal surface of Schottky structures is presented. The surface modes are only excited by light having the appropriate polarization; they are leaky at the metal-semiconductor interface and are thus radiated into the semiconductor, where they generate charge carriers. By this mechanism the photocurrent of the device is enhanced and depends strongly on the polarization angle of the incident light. By use of two detectors with different grating orientations the polarization of the light can be determined unambiguously.

Surface plasmon polariton enhanced light emission from Schottky diodes

We have investigated the light emission from forward‐ and reverse‐biased sinusoidally structured Ag/n‐GaAs Schottky diodes. Sinusoidally structured Schottky junctions show increased light emission because of the radiative decay of excited surface plasmon polaritons, resulting in drastically enhanced quantum efficiency. A model explaining excitation and emission of surface plasmon polaritons is presented.

Surface plasmon enhanced quantum efficiency of metal‐insulator‐semiconductor junctions in the visible

Narrowband photosignals with quantum efficiencies up to 30% are observed on Al‐SiO2‐p‐Si junctions. The frequency selective photosignals are due to surface plasmon polaritons confined to the metal‐air interface excited by grating coupling. The best results are achieved with Ag‐Al‐SiO2‐p‐Si junctions providing a 12‐nm linewidth and a signal to background ratio of 7:1 at a wavelength of 632.8 nm. The spectral sensitivity of these photodetectors is tunable over the whole visible spectrum either by a variation of the tilt angle or by a dielectric coating.

Surface plasmon polariton enhanced photoconductivity of tunnel junctions in the visible

We have investigated the influence of surface plasmon polaritons (SPP’s) on the reflection spectra of Ag‐Al2O2‐Al and Al‐AL2O2‐Al junctions in the visible range. The SPP’s were excited via sinusoidal grating structures. The SPP photon coupling efficiency was optimized as a function of the grating modulation height and dielectric coatings. For optimum coupling conditions a narrowband photoresponse of up to 60 mV/W into a 100‐Ω impedance at 632,8 nm was achieved. The narrowband (3–6 nm wide) photosignal is more than an order of magnitude higher than a broadband background signal. The color sensitivity is varied over the whole visible range with different dielectric coatings.

Frequency- and polarization-selective Schottky detectors in the visible and near ultraviolet

The influence of dielectric coatings on the photoresponsivity of metal-insulator-semiconductor structures on holographic submicrometer sinusoidal grating structures is investigated. Narrow-band photodetectors are realized based on the excitation of transverse electric modes and surface plasmon polaritons in the vacuum-MgF(2)-Al or vacuum-SiO(2)-A1 layer system on Si substrates. These detectors are sensitive to either s- or p-polarized light. Quantum efficiencies up to 20% and a linewidth of 18 mm were achieved with transverse electric modes at a wavelength lambda = 325 nm. The resonances are tunable from the ultraviolet into the visible regime by variation of the dielectric film thickness.

Fowler―Nordheim tunneling and conduction-band discontinuity in GaAs/GaAlAs high electron mobility transistor structures

Oscillatory structure is observed in the dI/dV and d2I/dV2 characteristics of conventional GaAs/GaAlAs high electron mobility transistor samples at liquid‐helium temperature, which can be explained using a Fowler–Nordheim tunneling theory. The position of the oscillations allows a determination of the conduction‐band discontinuity, and the depth of the deep donor levels in the GaAlAs for high aluminum concentrations. The fit of the data gives a value of ΔEc/ΔEg=0.61±0.04 for aluminum concentration 30, 36, and 40%. The deep donor level in the GaAlAs was determined to be 130 meV below the conduction band.

Polarization- and wavelength-selective photodetectors

A photodetector that is selective to the polarization, the frequency, and the angle of incident light is presented. Surface plasma modes excited at the surface of a semiconductor–metal–insulator structure provide selective coupling of light into the semiconductor with increased quantum efficiency. Two types of surface modes (TM0 and TE0) are realized by special choices of grating periodicity and insulator film thickness. TM0 modes have a resonant sensitivity to p-polarized light, whereas TE0 modes have a resonant sensitivity to s-polarized light. In addition, for both types of mode the resonance frequency is tunable in a wide range. By combining the selective properties of the surface modes with conventional photodetective devices, we can realize frequency, polarization, and angle-dependent detectors.

Leaky modes in metal‐semiconductor junctions

The reradiation of leaky surface plasmon polaritons into the semiconductor of a sinusoidally structured Schottky structure is investigated, to our knowledge for the first time. One of the two possible plasmon modes is bound at the metal‐air interface, and is leaky at the interface between the metal film and the semiconductor. It is reradiated into the semiconductor either directly or by coupling with the grating. Therefore, emission of light from the back surface of the sample can be measured at two different angles of observation. The intensities of the two single emission beams and their ratios were measured at various thicknesses of the metal film and were found to be strongly dependent on this parameter.

Electronic lifetimes in excited state Landau levels

We have determined for the first time the inter-Landau level lifetimes in GaAs/GaAlAs heterostructures in the spin polarized region (filling factor <1). Intensity-dependent cyclotron resonance absorption has been measured using a high-intensity optically pumped far-infrared (FIR) laser. A detailed analysis of the lineshape of the cyclotron resonance absorption within a Drude model shows saturation at intensities of 0.1 W cm-2. The electronic lifetimes deduced using a three-level model depend inversely on the electron concentration in the excited Landau level, indicating electron-electron scattering to be the dominant relaxation mechanism.

Tunable cyclotron resonance-laser in p-Ge

Stimulated far infrared radiation is observed due to cyclotron emission in the light hole band of p-Ge. For the first time the authors have observed in samples with an acceptor concentration of 8*1012 cm-3 an extended lasing range between 1.4 and 3.7 T, corresponding to a frequency range between 28 and 76 cm-1. For a higher doping of 5*1013 cm-3 the magnetic field range lies between 3 and 4.5 T with frequencies between 60 and 90 cm-1. For the latter sample they have found a maximum output power of 0.3 W. They have carried out a detailed study of the emission frequency and of cyclotron resonance absorption as a function of the applied magnetic field. A substantially improved calculation of the Landau levels in crossed fields including non-parabolicity effects was performed, to make a quantitative assignment of the transitions involved.