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ZnO films that have been used as active layers of optically pumped lasers are investigated by a number of optical and photoelectric techniques, such as transmission, reflectivity, photoluminescence and direct and alternating photocurrents. Homogeneity with respect to "bulk" and surface properties is evaluated. The spectral position of the lowest intrinsic exciton peak E-x((A,B)) is determined to be at (3.323 +/- 0.002) eV at 295 K. In spite of the rather small thickness of about 0.5 mu m, the samples do not exhibit strain-induced modifications of the optical properties at the band edge. A deep level is found to be responsible for the room temperature photocurrent, and excitonic features appear as absorption lines. On the other hand, excitonic photocurrent peaks are observed at low temperatures; however, the conduction mechanism still remains defect related.

Theoretical Analysis of the Spectral Photocurrent Distribution of Semiconductors

Thin-film preparation and its controlled mastery – specifically of semiconductors – became imperative for modern devices including all kind of applications such as electronics, optoelectronics, photonics, and superconductivity. Many methods and their technological applications have been explored and studied during the last decades (George, 1992, Smith, 1995, Ullrich et al. 1988, Bouchenaki et al., 1991 a, Bouchenaki et al., 1991 b, Ullrich et al., 1992, Ullrich and Kobayashi, 1995): Vacuum evaporation, molecular beam epitaxy (MBE), spray pyrolysis, closed-space deposition, sputtering, and pulsed-laser deposition (PLD). The difference between the latter and the aforementioned methods is that the film deposition process takes place only by photons, which naturally do not effect, alter or contaminate the ambient conditions of the substrate, which is kept in vacuum (typically 10-6 torr≈1.3×10-4 Pa). This feature puts PLD on top of the stoichiometry maintaining thin-film deposition methods. However, theory does not go along with reality all the time because the intrinsic atomic target features might influence the stoichiometry as well – for example PLD of CdS leads most of the time to slightly Cd enriched films. It is presumed that the heavier Cd atoms displace some of the S atoms from their designated target-to-substrate transfer path. This brings us to the basics of PLD – how does it work? The ablating light, which is provided by a pulsed laser, hits the substrate and, in case the convolution of laser fluence (i.e., the incident laser energy by illuminated area and pulse) and absorption is sufficiently high, material is ablated from the target. As an example, the deposition rates vs. fluence for different laser wavelengths of GaAs are shown in Fig. 1. The threshold fluence at 355 nm and 532 nm is at around 0.3 J/cm2, whereas at 1064 nm, the ablation onset requires higher fluence of approximately 0.5 J/cm2 due to weaker absorption of the infrared laser pulses. The qualitative appearance of the rates is the same at all wavelengths. Beyond threshold, the inset in Fig. 1 shows that the ablation rate exponentially increases with the fluence (F), i.e., ∝exp(kF), where k=6.0, 6.7, and 5.9, at 355 nm, 532 nm, and 1064 nm, respectively, followed by a fairly linear growth, which finally turns to a flat saturating rate of the ablated material. However, Fig. 2 shows that the deposition rate depends on the material – apparently the same fluence ablates more material from the ionically bonded IIVI compound CdS than from the covalently bonded III-V compound GaAs. The deposition rates have been recorded with the Sloan 200 monitor using a quartz crystal in the vacuum chamber.

Ein über 12 Jahre brütend kontrolliertes Steinkauz-Weibchen zeigte eine hohe Brutortstreue und Partnertreue über drei Jahre. In 11 Brutjahren legte es 49 Eier, aus denen 36 Nestlinge das Beringungsalter (10.-14. Lebenstag) erreichten. Ab dem Alter von 10 Jahren wurden durchschnittlich 0,8 Eier pro Jahr weniger gelegt. Von den 36 Nachkommen siedelten sich 2 Weibchen und 1 Männchen selbst wieder in der untersuchten Population an. Bis zum Alter von 9 Jahren lässt sich ein deutlicher Zusammenhang zwischen Bestandsdichte der Feldmaus als Hauptbeute und dem Termin des Legebeginns feststellen. A female of the little owl has been observed breeding over 12 years in a Southwestern German study area. The bird showed a high degree of nest site fidelity and a partner fidelity over three years. During 11 breeding periods the female incubated 49 eggs with a breeding success of 36 nestlings which reached the age of ringing (day of life 10 - 14). From the age of 10 years onwards average clutch size was reduced by 0.8 eggs per year. Out of 36 offspring two females and one male were recruited to the same studied population. Up to an age of 9 years a clear relationship persists between density of the main prey, the field vole Microtus arvalis and the date of the first egg.