In the presented work, we have developed VLSI technology processes for new prototype sensors based on the synthesis of boron doped nanocrystalline diamond (B-NCD) and silicon based commercial detectors. The process is based on commercial passivated implanted planar silicon (PIPS) devices of PD450 and CAM450 types (CANBERRA). A layer of B-NCD of several hundred nanometers thickness and boron concentration up to 1021 atoms/cm3 is grown on the SiOx passivation layer in an ellipsoidal plasma enhanced chemical vapor deposition (PECVD) reactor at temperatures from 520-750°C, in hydrogen atmosphere. . The diamond electrode is dry chemically structured and aluminum electrodes are realized before mounting in a three-fold housing for measurements in aqueous solution. The prototype sensors show an alpha spectroscopy resolution of 100 keV for 241Am electroprecipitated from liquid solution.

To counteract plasma instabilities like Neoclassical Tearing Modes (NTM-modes) in nuclear fusion reactors (JET, ITER, DEMO) high power microwaves are used for the Electron Cyclotron Resonance Heating (ECRH) and for the plasma current drive (CD). The foreseen power level for ITER (Cadarache, France) is Ptot = 24 MW at f = 170 GHz. Each transmission line is designed for a maximum of 2 MW power. The vacuum and tritium barrier to the ITER vacuum vessel is realized by a CVD diamond disk window assembly. Diamond has an extremely high thermal conductivity of about k = 2100 W/Km and a very low loss tangent of tan δ < 10-5 for this frequency and shows therefore a very small microwave absorption. The normalized absorbed power A=Pabs/P0 can be calculated as A = (f/c) • π • (1+εr‘) • tan δ • t (with the rule of thumb estimate: (f/c)=0.5 mm-1; π • (1+εr‘) = 20; tan δ =10-5; A=10-4 • t [mm]); i.e. each t = 1 mm thickness of diamond absorbs Pabs = 100 W of Po = 1 MW microwave power transmitted through the CVD diamond window with an effective tanδ of 10-5.

AlGaN/GaN pH sensitive devices were functionalized and passivated for the use as selective bio-sensors. For the passivation, a multilayer of SiO2 and SiNx is proposed, which stabilizes the pH-sensor, is biocompatible and has no negative impact on the following bio-functionalization. The functionalization of the GaN-surface was achieved by covalent bonding of 10-amino-dec-1-ene molecules by a photochemical process. After two different surface preparations islands of TFAAD are growing on the sensor surface by exposure with UV-light. In dependence on the surface pre-treatment and the illumination wavelength the first monolayer is completed after 3 h or 7 h exposure time dependent on the pre-treatment and illumination wavelength. Further exposure results in thicker films as a consequence of cross polymerization. The bonding to the sensor surface was analyzed by X-ray photoelectron spectroscopy, while the thickness of the functionalization was determined by atomic force microscopy scratching experiments. These functionalized devices based on the pH-sensitive AlGaN/GaN ISFET will establish a new family of adaptive, selective biomolecular sensors such as selective, reusable DNA sensors.

Free-standing GaN crystals are produced from 200-300 µn thick GaN films grown on 2 inch sapphire substrates by hydride vapor phase epitaxy. The GaN films are separated from the growth substrate by laser-induced liftoff, using a pulsed laser to thermally decompose a thin layer of GaN close to the film-substrate interface. The free-standing films are polished and used for the homoepitaxial growth of high quality GaN layers by metalorganic chemical vapor deposition. The structural and optical properties of the homoepitaxial films in comparison to layers grown on sapphire are significantly improved, mainly because of lower dislocation density and surface roughness as low as 5×106 cm2 and 0.2 nm, respectively.

Laser-induced thermal decomposition is also applied to achieve etching of GaN. At exposures of 500 mJ/cm2 with 355 nm light, etch rates of up to 90 nm for one pulse are obtained. Illumination with an interference grating is used to produce trenches as narrow as 100 nm or sinusoidal surface patterns with a period of 260 nm. Such surface morphologies are very useful for the processing of anti-reflection coatings or distributed Bragg reflectors.

Transient reflectivity experiments have been performed to measure the dynamics of laser-induced melting of amorphous silicon (a-Si) and the crystallization to μ-Si of films with different thicknesses on Corning 7059 glass. The laser-induced melting takes place with a velocity of 13 to 24 m/s, while the solidification is about a factor 10 slower. The crystallization starts at the Si/glass interface and at the surface. In the center of the films, Si remains liquid for an extended period of time. The crystallization dynamics point towards an heterogeneous morphology of laser-crystallized Si, where the surface and the interface layers are composed of small grains and the bulk of larger grains.

The preparation of seed lattices, using three interfering beams (TIB) from a pulsed Nd:YAG laser in a-Si layers of 100 to 400 nm thickness is introduced and applied for seeded laser or thermally induced crystallization of a-Si on Corning 7059 glass. The structural and electronic properties of the μc-Si layers are investigated by X-ray, electron- and atomic force microscopy, Hall and conductivity measurements. In highly boron-doped μc-Si, grains up to 1.3 μm in diameter are detected, giving rise ti conductivities of ≃ 2000 S/cm and hole mobilities of ≃ 10cm2/Vs.

Laser interference structuring with a pulsed Nd:YAG laser set-up is introduced and typical geometric dimensions and limitations are discussed. Intensity modulated laser beams are used to recrystallize amorphous silicon layers periodically at the intensity maxima. Stripe or tip structures of multi-crystalline (mc) silicon with sub-micrometer dimensions are shown. Structural, electronic and optical properties of the mc-Si structures are discussed. A hybrid thin film p-i-n solar cell architecture is described where the textured TCO is replaced by a flat TCO and a laterally structured boron doped mc-Si window layer. Light trapping, light diffraction and higher internal electric fields are proposed to be the main advantages of such a solar cell.

Transient grating (TG) experiments were performed to study carrier diffusion and recombination in amorphous silicon films (a-Si:H) at high light intensities using 8 ns pulses from a frequency-doubled Nd:YAG laser. The ambipolar diffusion coefficients reached about 10−2cm2/s, which is 2 orders of magnitude larger than the steady-state value. Similar results were obtained in intrinsic, p-, and n-doped a-Si:H films, indicating that the diffusion coefficients in all cases reflect the near band edge mobility of the slower carriers, that is holes. In particular, the p-type sample shows an initially fast, then a slow grating efficiency decay, consistent with dispersive transport.

Hall experiments on a series of microcrystalline, microcrystalline-amorphous, amorphous and crystalline silicon samples with varying defect densities are presented and discussed. Normal Hall effect signatures on boron and phosphorus doped hydrogenated amorphous silicon are detected. We interpret these results to be due to a small volume fraction of nanocrystalline Si, which falls below the detection limits of Raman experiments. Hydrogenated amorphous silicon, prepared under conditions far away from microcrystalline growth, shows the known double sign anomaly, Sign reversals in c-Si, where the disorder is increased by Si implantation up to very high levels, could not be detected.

CVD diamond films with nitrogen content varying from 10 ppm to 132 ppm have been studied by electron spin resonance (ESR), light-induced ESR (LESR) as well as spin-dependent conductivity (SDC). Two characteristic signals have been observed. A carbon-related defect line with g = 2.0029 ± 0.0002 and width 4 ± 1 G, is observed in ESR, LESR and SDC. The intensity of this line measured by ESR increases linearly with nitrogen content. For low-defect-density samples, or after illuminating the high-defect-density samples with UV light, a second signal is observed both in ESR and LESR, but not in SDC, with a central line at g = 2.0024 ± 0.001 and width 0.2 ± 0.1 G and related hyperfine satellites ≈30 G away from the central line. This line is assigned to isolated substitutional nitrogen, the so-called P1 center. The density of N-related paramagnetic states is strongly affected by illumination and heat treatments. Spin-dependent conductivity measurements show that the dark conductivity at room temperature in CVD-diamond is dominated by hopping at the g = 2.0029 defects.

By using a Nd: YAG-pumped optical parametric oscillator (OPO) as excitation light source (8 ns pulse width), the dynamic range of photothermal deflection spectroseopy (PDS) is increased by a factor up to 1000. This enables the study of nonlinear defect absorption in intrinsic, phosphorus and boron doped a-Si:H. To probe nonlinear absorption of defects, the intensity of the fundamental emission of the Nd:YAG (1064 nm) has been varied over three orders of magnitude. For intensities greater than 1024 photons/ (cm2s), a significant increase of a by a factor 1.4 in p-, 1.2 in i-, and 1.15 in n-a-Si:H is detected. From electron spin resonance (ESR) and transient photoconductivity experiments on intrinsic a-Si:H, a bleaching of the defect density by electron excitation into the conduction band is measured. A hole-like signature in the ESR spectra indicates that electrons from the valence band are excited into the defect band as well. The data are interpreted based on a model for IR-induced nonlinear optical effects.

Hall experiments performed on intrinsic, phosphorus and boron doped a-Si:H and a-SiC:H in the temperature regime 200 K ≤ T ≤400 K are introduced and discussed. The data confirm the double sign anomaly meaning the Hall coefficient is p-type on intrinsic and phosphorus doped a-Si:H and a-SiC:H, and n-type on boron doped a-Si:H. The Hall mobilities, μH, are significantly smaller than the drift mobilities, decreasing with increasing doping and/or carbon content. μH of holes is about half that for electron which indicate that μH scales approximately with 1/Eg where Eg is the tail slope. The presented interpretation of the Hall coefficient, that is introduced to be a function of Hall- and drift-mobility, enables the accurate determination of the carrier density in intrinsic and doped amorphous silicon and alloys from Hall data.

The kinetics of small changes from thermal equilibrium are measured and simulated for thermally induced metastable changes. We find that only a distribution of rate constants is consistent with the data, and therefore we can eliminate certain types of microscopic models for metastability which depend on a single variable such as the carrier density.

Low temperature, high field properties of electron and hole transport are investigated by time-of-flight (TOF), steady-state and transient space charge limited current (SCLC) experiments on intrinsic a-Si:H. Charge collection and TOF experiments performed at T= 80 K reveal hole μτ-products of = 8 × 10-10 cm2/V and hole mobilities μ ≤ 9×10-3 cm2/Vs. The field effect on hole thermalization is demonstrated by evaluation of the post transit current decay. SCLC experiments on p+ -i-n+ (electron transport) and p + -i-n+ (hole transport) configurations are introduced and interpreted in terms of field enhanced conductivity and mobility. The experiments demonstrate the overwhelming field effect on carrier hopping in the band tail regions of a-Si:H. Considerably higher fields have to be applied in the case of hole transport than electron transport to achieve comparable conductivities; this is discussed on the basis of the different tail state distributions and localization lengths.

Small temperature-induced perturbations from thermodynamic equilibrium of doped hydrogenated amorphous silicon (a-Si:H) are explored by dark conductivity measurements. The equilibration kinetics reveal significant differences between phosphorus and boron doping. Raising the temperature leads to an increase of electron/hole densities which are related to the activation of additional dopants, while a decrease of temperature causes the opposite effect of dopant passivation. The creation kinetics of P doped a-Si:H is stretched exponential with a temperature independent β value of 0.85 whereas dopant passivation in the same temperature range is also stretched exponential decay, but with values for β < 0.8. In contrast, the kinetics of boron activation and passivation are stretched exponential with equal β values. The time constant τ to achieve thermodynamic equilibrium for both activation and passivation is thermally activated with energies ≃ 1.1 eV for P and B doped a-Si:H. τ depends weakly on the degree of perturbation. A discussion and interpretation of the data based on hydrogen migration in a-Si:H is given.

Time-of-flight and charge collection experiments performed on a-Si:H p-i-n structures in the temperature range 40–300K reveal electron drift mobilities which continuously decrease with decreasing temperature and electric field. At 40K, fields ≥ 2×105 V/cm are necessary to collect almost all carriers. A discussion of the data on the basis of a nearest neighbour hopping model shows the significant influence of the applied field on the hopping down process of electrons. Field-induced re-emission of deep trapped carriers back into shallow tail states establishes a narrow band of energy levels where electrons accumulate and propagate. The band width and energy position of the accumulation levels in the tail depends strongly on the applied field and the distribution of localized states. With increasing electric field, it shifts up in energy closer towards the conduction band edge and changes the hopping mobility for orders of magnitude. The calculated and experimental data are in reasonable agreement with the model of a hybrid distribution of localized states.

The remote plasma deposition process was studied by optical emission spectroscopy using Ne and N2 to detect He-metastables. a- Ge:H was prepared and its optoelectronic and structural properties were characterized. AM 1.5 photoconductivities around 10−6(Ωcm)−1 were obtained in intrinsic material with the Fermi level position lying near midgap. However, even in the best film the defect density is higher than 1017cm−3.

The thermalization of electrons in the medium temperature range (120K ≤ T ≤ 200K) is investigated by time-of-flight experiments on a-SiGe:H mim structures. The evaluation of the pre-transit current decay reveals a dual slope characteristic which reflects an initial hopping down (I ∼ t−1) followed by a thermally activated (I ∼ t−p 0 < p < 1) process. The transition time from hopping down to multiple trapping sensitively depends on temperature and alloy composition. The experimentally deduced features can be explained by the increased tail state density at the conduction band mobility edge of a-SiGe:H samples compared to a-Si:H.