The optical and electro-optical properties of epitaxially grown thin films of ferroelectric BaTiO3 on MgO substrates have been established and high quality Mach-Zehnder waveguide modulators have been demonstrated. As a next step towards the integration of ferroelectric thin films on different substrates, we have modified the growth conditions by lowering the growth temperature to study polycrystalline, but still highly transparent BaTiO3 (BTO) films. Polycrystalline BTO on MgO substrates has been grown by pulsed laser deposition (PLD). The growth temperature was reduced from 800 °C to 400 °C at an oxygen pressure of 2×10-3 mbar. Although polycrystalline, the BTO is still birefringent with no= 2.32 and ne = 2.30. Ridge waveguides have been formed by ion beam etching. The estimated waveguide propagation loss is 4 dB/cm at 633 nm. Electro-optic Mach-Zehnder modulators have been realized. Using 3 mm long electrodes with a spacing of 10 μm, a Vπ voltage of 14 V was obtained at 633 nm wavelength. This is half of the observed effective electro-optic coefficient measured at epitaxial BTO films. At 1.5 μm wavelength similar results were observed.

High quality BaTiO3 epitaxial thin films on MgO substrates have been grown by pulsed laser deposition (PLD). Both c-axis and a-axis orientated BaTiO3 were studied. Mach-Zehnder (M-Z) optical waveguide modulators have been fabricated by ion beam etching. The BaTiO3 waveguide propagation losses are 1-2 dB/cm. Electro-optic modulation has been demonstrated with Vπ = 6.3 V at a wavelength of 633 nm and Vπ = 9.5 V at a wavelength of 1550 nm for the aaxis samples and with Vπ = 8 V at 633 nm wavelength and Vπ = 15 V at 1550 nm for the c-axis samples. Modelling of the modulators gave the Pockels coefficient r51 = 80 pm/V for the c-axis film and an effective Pockels coefficient reff =734pm/V for the a-axis films at 633nm wavelength.

We have prepared single crystalline epitaxial PbZr0.52Ti0.48O3 (PZT) and BaTiO3 (BTO) thin films on single crystalline epitaxial SrRuO3 (SRO) thin films grown on SrTiO3 (100) (STO) substrates. PZT and SRO thin films were grown using high-pressure on-axis sputtering and BTO using pulsed laser deposition (PLD). The film thickness ranged between 12 to 165 nm. Their excellent structural properties, surface smoothness and interface sharpness were demonstrated by X-Ray Diffraction measurements (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and Atomic Force Microscopy (AFM). Rutherford Backscattering Spectrometry and Channeling measurements (RBS/C) were used to analyze stoichiometry and crystalline quality. Ferroelectric hysteresis loops were obtained for all films of a thickness down to 12 nm showing a decrease in the remanent polarization Pr and an increase in the coercive field Ec towards thinner film thicknesses. Furthermore we have prepared tunneling junctions with a PZT or BTO barrier thickness of 3-6 nm. Reproducible bi-stable I-V-curves and bias dependence of the conductance were obtained suggesting an influence of the ferroelectric properties of the barrier material on the tunnel current.

Efficient infra-red and visible electroluminescence(EL) has been obtained from implanted rare earth ions in the SiO2 of a silicon-metal-oxide-semiconductor (MOS) diode structure at room temperature. The rare earth ions are excited by the direct impact of hot electrons tunneling through the oxide at electric fields larger than 6 MV/cm. The internal quantum efficiencies of Er and Tb implanted MOS diodes are estimated to be 10 % and 3 %, respectively. The hgh quantum efficiency is due to the high impact excitation cross-section of more than 10− 15cm2. These observations on MOS structures are an experimental proof for efficient light generation by hot electron impact.

We have studied different metal-silicon-metal (MSM) Schottky barrier photodiodes for the detection of visible and infrared light. We investigated the different Schottky barriers from Ti, Cr and Pt. At infrared wavelengths, the Schottky contacts provide electrons and holes by “internal photoemission” into the Si. The lowest Schottky barrier determines the long wavelength cutoff and the current noise. The temporal response was measured byultrashort (100 fs) laser pulses from a Ti:A1203 laser, which were converted by an optical parametric oscillator to a wavelength of 1.1 to 1.6 μm. The measurements were performed between 30 K and room temperature. The best detectors show a pulse width of 3.2ps FWHM at 1.25 μm wavelength and room temperature. To our knowledge this is the fastest infrared response for silicon based diodes ever reported.

In the process of developing thin film electro-optical waveguides we investigated the influence of different substrates on the optical and structural properties of epitaxial BaTiO3 thin films. These films are grown by on-axis pulsed laser deposition (PLD) on MgO(100), MgAl2O4(100), SrTiO3(100) and MgO buffered A12O3(1102) substrates. The waveguide losses and the refractive indices were measured with a prism coupling setup. The optical data are correlated to the results of Rutherford backscattering spectrometry/ion channeling (RBS/C). X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). BaTiO3 films on MgO(100) substrates show planar waveguide losses of 3 dB/cm and ridge waveguide losses of 5 dB/cm at a wavelength of 633 nm.

Within our program to develop ferroelectric thin film optical waveguides, we have studied the growth of epitaxial waveguides BaTiO3 on r-plane sapphire substrates with a MgO buffer layer. The films were prepared by pulsed laser deposition (PLD). Their structural properties were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Rutherford backscattering (RBS) in random and channeling (RBS-c) configuration and atomic force microscopy (AFM). They displayed good crystalline quality, characterized by an RBS-c minimum yield of about 4–6%, a full width at half maximum (FWHM) of the XRD rocking curve measurement of the BaTiO3(200) reflection of 0.32° and a rms roughness of 1.2 nm in a film of ∼ 1.0 μm thickness. The epitaxial relationship was found to be BaTiO3(100) // MgO(100) // A12O3(1102). The refractive index, the birefringence and the optical losses have been measured.

We present data on the fabrication process of optical waveguides from four different polymers, which have been patterned either by standard lithographical masking and reactive ion beam etching (RIE) or by direct lithographical exposure of photosensitive material. Three of the resists were directly photosensitive, they could be exposed and developed. Thereafter they can be cured and remain stable. Waveguide losses of 3.5 dB/cm had to be accepted for the photosensitive materials, while the non-sensitive polymers formed very good guides (0.8 dB/cm), but were more difficult to process. We demonstrate the coupling of the strip waveguides to optical fibers on one side and to very thin metal-semiconductor-metal (MSM) photodetectors at the other side. A beam propagation method computer code has been used to evaluate the best coupling efficiencies between the guides and the detectors, which are ultrafast (3.5 ps FWHM) due to their very thin silicon slab design (Si thickness 400 nm, sandwiched between two Schottky contacts).

Photodetectors must provide fast and efficient conversion of photons to charge carriers. When considering semiconductor light sources, the indirect bandgap of silicon and germanium represents a serious obstacle to radiative electron-hole recombinations. Momentum conservation demands the simultaneous interaction of the electron-hole pair with a momentum-matching phonon. As a consequence, radiative recombinations are five orders of magnitude less probable in Si if compared to a direct semiconductor such as GaAs.

Although the absorption of a photon and the generation of an electron-hole pair may be considered as the inverse process to emission, photon absorption within indirect semiconductors is a highly probable process if the photon energy is sufficient to bridge the energy gap in a direct process. The resulting electronhole pair is created in an excited state and relaxes sequentially. The ubiquitous-silicon solar cells operate this way. In the visible spectral range, Si photodetectors have demonstrated fast and efficient performance, being readily adapted for opto electronic applications and being fully compatible to standard-silicon processing schemes.

The potential of silicon-based designs for various optoelectronic functions is discussed. Sibased light detectors are the most advanced, especially in the form of metal-Si-metal (MSM) photodetectors. They use Si band to band absorption for visible light and Schottky-barrier emission for the infrared (IR). The different light sources show rapid progress, but still face challenges to reach a quantum efficiency of 10−2. In addition to the intrinsic silicon based designs, some new Si breadboard concepts are shown: especially for waveguides, modulators and all-optical amplifiers, it may be advantageous to add entirely different materials (polymers, glasses, BaTiO3 or Al2O3) onto the Si wafer.

Technologically interesting optical materials such as BaTiO3 and KnbO3 are difficult to grow as single crystals of large dimensions. Thin film techniques can overcome this problem by synthesizing these materials on commercially available substrates. We demonstrate the deposition of single crystalline BaTiO3 and KnbO3 on MgO, SrTiO3 and buffered MgO substrates by Pulsed Laser Deposition (PLD). The samples are characterized by Rutherford Backscattering Spectrometry / Channeling (RBS/C), X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). We found excellent crystalline quality, confirmed by RBS/C minimum yield values of 2 % and a FWHM of 0.36° of the BaTiO3(002) rocking curve. Even films of a few microns thickness have been grown without loss of crystalline perfection, and all films show very flat surfaces. The RMS roughness of a 950 nm BaTiO3 film was found to be 1.1 nm.

We report on a systematic study of the growth parameters of erbium-oxygen-doped silicon grown by molecular beam epitaxy. The surface quality of the grown layers was measured in situ by RHEED. The samples were characterized by photoluminescence measurements and SIMS. An Er-O-doped Si light emitting diode grown with the optimized parameters is presented.

We present a new mask design and implantation scheme, which uses one single ion implantation step of 2 MeV He ions at a dose of 7–1014 to 3–1015 He/cm2 to form channel waveguides in single crystalline KNbO3. The special processing of the photoresist mask enables the formation of channel waveguides with a trapezoidal-shaped cross section, providing for the first time simultaneous confinement of both TE and TM modes in a permanent KNbO3 channel waveguide. 2.6 mW second-harmonic blue light at 441 nm was generated in a 5.8 mm long guide for a fundamental power of approx. 200 mW.

The growth of thin films of LiNbO3 and Er:LiNbO3 on LiNbO3 single crystals produced by pulsed laser deposition (PLD) was studied. Samples were characterized by RBS/Channeling Spectrometry, X-ray diffraction measurements, Secondary Ion Mass Spectroscopy (SIMS) and photoluminescence (PL) measurements. Film preparation is performed in a two-step process including deposition and in-situ-annealing. Buried Er doped layers of approx. 800 nm thickness were grown.

We present investigations of YBa2Cu3O7-x, thin films deposited on Silicon on Sapphire (SoS) substrates by pulsed laser deposition and dc sputtering. A compound buffer system consisting of YSZ and CeO2 is used for improved YBa2Cu3O7-x growth characteristics. The critical thickness of YBa2Cu3O7-x on CeO2/YSZ/SoS is determined to be 280 nm.

LiNbO3 single crystals were implanted with Er ions at 3.5 MeV with fluences up to 3*1016 Er/cm2 and subsequently annealed at 1060°C. The warm-up rate of the sample determines whether the implanted, amorphized surface layer recrystallizes via columnar or via layer-by-layer solid phase epitaxial (SPE) growth. The maximum concentration of optically active Er ions is determined to be 0.18 at.%.

The incorporation of Er into LiNbO3 is of great interest for fabricating waveguide lasers and amplifiers. We compare Er diffusion data with the results of Er implantation, performed at 3.6 MeV energy. Even after annealing for 4h at 1060°C, the resulting Er profiles display very good matching to the optical modes. The results of a theoretical gain estimate are presented.

We have implanted Nd and Er ions into x- and z-cut LiNbO3 single crystals. Rutherford backscattering spectrometry and channeling shows the recrystallization of the host during annealing and the rare earth diffusion. Nd and Er have different solubilities and different diffusion constants in LiNbO3. The solubility is strongly temperature dependent. The diffusion is substitutional, fastest parallel to c-axis of the LiNbO3 crystal and characterized by an activation energy of approximately 3.6 eV.

We have implanted Nd and Er ions into x- and z-cut LiNbC3 single crystals and investigated the recrystallization of the host and the rare earth solubility and diffusion. The diffusion is substitutional, fastest parallel to c-axis and characterized by an activation energy of 3.6 eV. Optical fluorescence experiments of Er3+ in a waveguide configuration show stimulated emission and amplification at 1.53, 1.55 and 1.56 μm wavelength.

We have used 2-MeV and 200-KeV He implantation into KNbO3 and LiNbO3 single crystals to generate a damaged layer of reduced optical index. MeV implantation enables the formation of optical waveguides of several µm thickness, which have been analyzed by dark and bright line spectroscopy in order to determine the refractive index profiles. In addition, 200-keV implants have been used to model the end-of-range-damage, which was measured by RBS/Channeling. KNbO3 and LiNbO3 show a distinctly different sensitivity of the radiation damage.