The role of ions on the growth of microcrystalline silicon films produced by the standard hydrogen dilution of silane in a radio frequency glow discharge is studied through the analysis of the structural properties of thick and thin films. Spectroscopic ellipsometry is shown to be a powerful technique to probe their in-depth structure. It allows to evidence a complex morphology consisting of an interface layer, a bulk layer, and a subsurface layer. The ion energy has been tuned by codepositing series of samples on the grounded electrode and on the powered electrode, as functions of pressure and power. On the one hand, reducing the ion energy through the increase of the total pressure and depositing on the grounded electrode, favors the formation of large grains and results in improved bulk transport properties, but leaves an amorphous interface layer with the substrate. On the other hand, we achieve fully crystallized films on glass substrates under conditions of high energy ion bombardment. We suggest that ion bombardment, and particularly the implantation of hydrogen ions, favors the formation of a porous layer where the nucleation of crystallites takes place. These results are further supported by in situ spectroscopic ellipsometry measurements of the film morphology as a function of the ion energy.

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We have studied structure and electrical properties of Si1−YGeY:H films deposited by low-frequency plasma-enhanced chemical vapor deposition over the entire composition range from Y = 0 to Y = 1. The deposition rate of the films and their structural and electrical properties were measured for various ratios of the germane/silane feed gases and with and without dilution by Ar and by H2. Structure and composition was studied by Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and Fourier transform infrared (FTIR) spectroscopy. Surface morphology was characterized by atomic force microscopy (AFM). We found that the deposition rate increased with Y, maximizing at Y = 1 without dilution. The relative rate of Ge and Si incorporation is affected by dilution. Hydrogen preferentially bonds to silicon. Hydrogen content decreases for increasing Y. In addition, optical measurements showed that as Y goes for 0 to 1, the Fermi level moves from mid gap to the conduction band edge; i.e., the films become more n-type. No correlation was found between the pre-exponential and the activation energy of conductivity. The behavior of the conductivity γ-factor suggests a local minimum in the density of states at E ≈ 0.33 eV for the films grown with or without H-dilution and E ≈ 0.25 eV for the films with Ar dilution.

The coherent optical response from 140 nm and 65 nm thick ZnO epitaxial layers is studied using transient four-wave-mixing spectroscopy with picosecond temporal resolution. Resonant excitation of neutral donor-bound excitons results in two-pulse and three-pulse photon echoes. For the donorbound A exciton (D 0 XA) at temperature of 1.8 K we evaluate optical coherence times T2 = 33−50 ps corresponding to homogeneous linewidths of 13 − 19 µeV, about two orders of magnitude smaller as compared with the inhomogeneous broadening of the optical transitions. The coherent dynamics is determined mainly by the population decay with time T1 = 30 − 40 ps, while pure dephasing is negligible in the studied high quality samples even for strong optical excitation. Temperature increase leads to a significant shortening of T2 due to interaction with acoustic phonons. In contrast, the loss of coherence of the donor-bound B exciton (D 0 XB) is significantly faster (T2 = 3.6 ps) and governed by pure dephasing processes.

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At the present time there are commercially available large un‐cooled micro‐bolometer arrays (as large as 1024×768 pixels) for a variety of thermal imaging applications. Different thermo‐sensing materials have been employed as thermo sensing elements as Vanadium Oxide (VOx), metals, and amorphous and polycrystalline semiconductors. Those materials present good characteristics but also have some disadvantages. As a consequence none of the commercially available arrays contain optimum pixels with an optimum thermo‐sensing material. This paper reviews the development of the un‐cooled bolometer technology and the research achievements on this area, with special attention on the key factors that would lead to improve the pixels performance characteristics. The work considers the R&D of microbolometer arrays and the integration with MEMS and IC technologies. A comparative study with the state of the art and data reported in literature is presented. Finally, further directions of uncooled bolometer based in thin films materials are also discussed in this paper. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)