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In this work, thin films of Indium Tin Oxide (ITO)-based materials were tested as potential candidates for mid-IR transparent contacts on Te-doped GaSb and Si-doped InAs semiconductor wafers. Since these contacts are devoted to be inserted in Sb-based devices which are generally MBE-grown at ∼450°C, low-temperature fabrication processes were particularly tested with a maximum temperature of annealing of 400°C. 50 nm-thick ITO films were deposited on glass, Te-doped GaSb and Si-doped InAs wafers and resistivity of 8.10−4 Ω.cm combined with ∼80% of transmittance at 2 μm and ohmic contacts with a specific resistance of 3.10−4 Ω.cm2 were obtained. Then, in order to improve these properties in the mid-IR, other ITO-based materials were tested: In doped ZnO (IZO) and Zn doped ITO (ITZO). The first results obtained on these materials show that the insertion of 10% of Zn in classical ITO structure results in a degradation of the electrical properties of the layer without a real impact on its optical transmittance near 2 μm. Concerning IZO, a large improvement of the transmittance in the whole visible-mid-IR wavelength range was observed for annealed samples at a temperature as low as 350°C. However, the electrical resistivity appears very sensible to the temperature of annealing.
GaN epilayers were grown by metal-organic vapor phase epitaxy (MOVPE) on
z- and x-cut lithium niobate substrates. Ex-situ characterizations of the
epilayers by means of scanning electron microscope, atomic force microscope,
X-ray diffraction and micro-Raman scattering measurements have revealed same
growth features on both substrates. The observation of the morphology shows
homogeneous and relatively smooth surface. The shape and density of GaN
islands as well as the observed columnar growth mode are not dependent of
the orientation of the LN substrates. The X-ray diffraction analysis of 450 nm thick GaN layers grown at 730 °C on z- and x-cuts showed that both GaN
layers reveal the same crystallographic orientation, i.e. c-axis
orientation normal to the substrate plane and in-plane orientation that
coincides with the primary axis of LN substrates. The Raman scattering
measurements confirm the growth of an oriented epitaxial GaN layer on LN
substrate. Moreover, the deposited layer exhibit a quite good homogeneity,
since the Raman spectra recorded for different positions in the layer do not
reveal any significant variations in their relative intensities and
Chemistry of co-evaporated CIGS surfaces submitted to chemical treatments relevant to fabrication steps were investigated by XPS and admittance spectroscopy. A Se XPS signal specific of the CIGS surfaces was identified. Surface states seen by Admittance and surface chemistry are seen to change significantly during the elaboration steps. Consequences for device elaboration are briefly discussed.
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