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Transmission electron microscopy studies of the microstructure of AuNiGe ohmic contact to n-type GaAs Microstructure analysis and contact resistance measurements of alloyed AuNiGe contacts to GaAs were performed to assist in the development of low resistance Ohmic contacts for metalsemiconductor field-effect transistor (MESFET) devices. The contact metals were prepared by sequential deposition of 100 nm of Au-27 at. % Ge, 35 nm Ni, and 50 nm Au onto sputter-cleaned GaAs wafers in which conducting channels were formed by Si doping to a level of about 1 X 10 18 cm -3. The contact resistances were determined by the transmission line method. Analysis of the substrate and the film microstructure was carried out by x-ray diffraction, Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS). A strong correlation between the contact resistance and the film microstructure was observed. Low resistances were observed when NiAs compounds containing Ge were in contact with GaAs and the {3-AuGa phase was concentrated near the top of the contact. High resistances were measured when free Au, the a-AuGa phase, or a NiGe compound were present. The temperature dependence of the contact resistance and the kinetics of compound formation were found to be influenced by the deposition sequence. Deposition of 5 nm Ni as a first layer significantly enhanced the formation of the NiAs compounds containing Ge, resulting in low contact resistance at a lower alloying temperature. However, a further increase in the thickness of the first Ni layer to 10

We develop an analytical model for calculating the diffuse reflectance of inhomogeneous films containing aligned microplatelets with diameters much greater than the wavelength. The scattering parameters are derived by modeling the platelets as one-dimensional thin films, and the overall diffuse reflectance of the slab is calculated using the Kubelka-Munk model. Our model predicts that reflection minima and maxima arising from coherent interference within the platelets are preserved in the diffuse reflectance of the disordered slab. Experimental validation of the model is provided by reflectance measurements (0.3–15 μm) of a solid aerosol film of aligned hexagonal boron nitride platelets.

There is considerable interest in understanding the surface oxidation reactions of transition-metal alloys with potentially useful magnetic properties. These reactions can either lead to passivation or corrosion of the magnetic film under normal atmospheric conditions. Little is known, however, about the surface oxidation reactions of MnFe. In the present study, thin films ofMnFe prepared by dc magnetron sputter deposition onto Si, Cu, and Ni 8o Fe 2o have been characterized magnetically by superconducting quantum interference device (SQUID) and vibrating sample magnetometer measurements and their surface chemistry has been followed by angle resolved xray photoelectron spectroscopy and ellipsometry. The reactivity of the clean MnFe surface with O 2 , H 2 0, and N2 was investigated. The interaction of MnFe with O 2 proceeds by preferential oxidation and surface segregation of Mn oxide. The final products of oxidation after a 66 OOO-L exposure are MnO and Fe 2 0 3 , in agreement with thermodynamic considerations. Compared to the reactivity of O 2 with MnFe, the adsorption of H 2 0 on MnFe is extremely sluggish, while N 2 does not adsorb at all. The controlled oxidation behavior ofMnFe is compared and contrasted to that observed for the related alloy NiFe and to that observed in air oxidation of both these alloys.