CuInSe2/CdS heterojunction diodes prepared entirely by chemical spray pyrolysis are investigated using admittance spectroscopy to obtain information on electrically active trapping centers within the CuInSe2. Because of the relatively large parallel leakage conductance associated with these devices, a frequency-swept admittance technique (stepped in temperature) is employed to differentiate between the loss signal due to trapping centers and the loss due to parallel conductance. The frequency-swept admittance technique is described and compared to the more conventional temperature-swept method. The devices used in this study exhibit one-sun efficiencies of 2.0%–3.0% and a forward current dominated by generation-recombination processes within the space charge region. Admittance spectra indicate a dominant hole trap is located approximately 270 meV above the valence band of the CuInSe2.
A new technique has been developed to fabricate submicron gates in GaAs metal–semiconductor field effect transistors (MESFETs) using simple contact lithography. The technique employs a multiple layer resist structure and angle evaporation to define a conformal aluminum mask above the wafer surface. The gate length of the aluminum mask is well controlled by an evaporation angle and a resist thickness. The pattern transfer to the wafer surface is compatible with a recessed gate technology. In a production environment, the process is capable of producing quarter-micron MESFETs with less than ±150 Å (1σ) gate length variation across a 2-in. wafer.
A simple and practical method is described for determining the residual stress in vapor deposited thin films that are less than 1000 Å in thickness. The method relies on the evaporation of thin films onto prefabricated micro-cantilever beams of SiO2. The vertical deflection at the end of the beam is measured using an optical microscope to determine the average film stress with a resolution of 25 MPa. Calculations show that the vapor deposition of metal films onto these beams does not induce significant heating, so the thermal component of residual film stress is minimal. The micro-cantilever technique is used to measure the film stress in 500 Å films of Al, Ti, Pt, Au, Ni, and Ge. These measured values are compared to similar measurements reported in the literature.
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