Ferroelectric capacitors having Pt bottom and top electrodes and a ferroelectric film of composition PbZr0.51Ti0.49O3 (PZT) were fabricated and investigated. The PZT films of thicknesses varying from 0.12 to 0.69 μm were prepared by organometallic chemical-vapor deposition. Annealed capacitors were investigated by capacitance, hysteresis, and pulse switching measurements. It is found that the thickness dependence of the reciprocal capacitance, the coercive voltage, and the polarization measured by pulse switching can all be explained by a blocking layer model, in which a dielectric layer of thickness dbl and relative permittivity εbl is situated between the PZT film and an electrode. It is shown that (i) the coercive field is independent of thickness having a value of 2.4 V/μm; (ii) the ratio εbl/dbl is in the range 20–28 nm−1; (iii) the voltage across the blocking layer is proportional to the polarization, Vbl=cP, where c=4.1±0.5 V m2/C; and (iv) the polarization depends on the electric field in the PZT layer, independent of thickness. Pulse switching endurance measurements showed that in the saturation range the fatigue for these ferroelectric capacitors is determined by the pulse voltage and is independent of the thickness.

The present work describes the study and improvement of the Epitaxial Lift-Off (ELO) technique, which is used to separate III/V device structures from their GaAs substrates. As a result the ELO method, initially able to separate millimetre sized GaAs layers with a lateral etch rate of about 0.3 mm/h, has been developed to a process capable to free entire 2″ epitaxial structures from their substrates with etch rates up to 30 mm/h. It is shown that with the right deposition and ELO strategy, the thin-film III/V structures can be adequately processed on both sides. In this way semi-transparent, bifacial solar cells on glass were produced with a total area efficiency in excess of 20% upon front side illumination and more than 15% upon back side illumination. The cell characteristics indicate that, once the thin film processing has been optimized, ELO cells require a significantly thinner base layer than regular III/V cells on a GaAs substrate and at the same time have the potential to reach a higher efficiency.

Centimeter sized, crack-free single crystal InGaP films of 1 μm thickness were released from GaAs substrates by a weight-induced epitaxial lift-off process. At room temperature, the lateral etch rate of the process as a function of the applied Al0.85Ga0.15As release layer thickness was found to have a maximum of 3 mm/h at 3 nm. Using 5-nm-thick AlAs release layers, the etch rate increased exponentially with temperature up to 11.2 mm/h at 80 °C. Correlation of the experimental data with the established theoretical description of the process indicate that the model is qualitatively correct but fails to predict the etch rates quantitatively by orders of magnitude.

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The switching time (ts) for polarization reversal in ferroelectric films of PbZr0.53Ti0.47O3 and La-substituted PbTiO3 has been investigated. The films were prepared by spin-on and metalorganic decomposition followed by processing into ferroelectric capacitors having electrode areas ranging from 9 to 50 000 μm2. Pulse measurements show that under all our experimental conditions ts is instrumentally limited and that therefore the true switching time is smaller than the experimental resolution of 1.8 ns. This very fast polarization reversal can be explained by a nucleation-rate-controlled switching mechanism.

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The epitaxial lift-off process allows the separation of a thin layer of III/V material from the substrate by selective etching of an intermediate AlAs layer with HF. In a theory proposed for this process, it was assumed that for every mole of AlAs dissolved three moles of H 2 gas are formed. In order to verify this assumption the reaction mechanism and stoichiometry were investigated in the present work. The solid, solution and gaseous reaction products of the etch process have been examined by a number of techniques. It was found that aluminum fluoride is formed, both in the solid form as well as in solution. Furthermore, instead of H 2 arsine (AsH 3 ) is formed in the etch process. Some oxygen-related arsenic compounds like AsO, AsOH, and AsO 2 have also been detected with gas chromatography/mass spectroscopy. The presence of oxygen in the etching environment accelerates the etching process, while a total absence of oxygen resulted in the process coming to a premature halt. It is argued that, in the absence of oxygen, the etching surface is stabilized, possibly by the sparingly soluble AlF 3 or by solid arsenic. The epitaxial lift-off ͑ELO͒ process allows the production of single-crystalline thin films of III/V materials. The technique is interesting for the optoelectronics industry, because the use of thin film devices results in a more efficient transfer of generated heat from device to carrier or heat sink and significantly reduces the amount of material needed by reuse of the substrates. Furthermore, ELO allows the integration of III/V-based components with, e.g., silicon-based devices.In 1978, Konagai et al. 1 first reported on peeled-film technology ͑PFT͒; they separated a Ϯ5 m thick GaAs epilayer from the GaAs substrate by etching a thin intermediate AlGaAs release layer with aqueous HF solution. It was found that this process stopped at certain depths, because etchant and reaction products could not be exchanged sufficiently fast through the narrow etch slit.2 In 1987, Yablonovitch et al. 3 reported that for thinner epilayers with a thickness in the order of 1 m this problem could be overcome by placing a droplet of black wax on top of the GaAs layer. The GaAs epilayers experience some stress due to the wax and curl up, thereby forcing open the small crevice between substrate and epilayer. As a result, the etch process, now referred to as ELO, no longer stopped at a certain depth. In a model to describe this process, Yablonovitch et al.3 assumed that in etching AlAs release layers with HF solution in water each mole of AlAs forms three moles of H 2 gas and that the out-diffusion of this H 2 gas through the etch crevice is the limiting factor for the lateral etch rate. By assuming the rate of diffusion of H 2 out of the etch slit to be equal to the rate of production at the etch front, the maximum attainable etch rate was found to bewhere N and n are the molar concentrations of AlAs and dissolved H 2 , respectively, D the diffusion constant of H 2 in the solution, R the radius of curvature of the fi...