Method and apparatus for determining minority carrier diffusion

Details Method and apparatus for determining minority carrier diffusion Method and apparatus for determining minority carrier diffusion

1981-07-06

1984-02-21

Karlsen, Ernest F.

Electricity: measuring and testing

Measuring, testing, or sensing electricity, per se

With rotor

324158R, G01R 3126

Patent

active

044332882

ABSTRACT:
Method and apparatus are provided for determining the diffusion length of minority carriers in semiconductor material, particularly amorphous silicon, which has a significantly small minority carrier diffusion length using the constant magnitude surface-photovoltage (SPV) method. Steady or modulated illumination at several wavelengths provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPV for each wavelength. A probe electrode immersed in an electrolyte solution containing redox couples (preferably quinhydrone) having an oxidation-reduction potential (E) in the order of +0.6 to -1.65 volts couples the SPV to a measurement system. The redox couple solution functions to create a liquid Schottky barrier at the surface of the material. The Schottky barrier is contacted by merely placing the probe in the solution. The redox solution is placed over and in contact with the material to be tested and light is passed through the solution to generate the SPV. To compensate for colored redox solutions a portion of the redox solution not over the material is also illuminated for determining the color compensated light intensity. Steady red light is also used as an optical bias to reduce deleterious space-charge effects that occur in amorphous silicon.

REFERENCES:
patent: 4051437 (1977-09-01), Lile et al.
patent: 4333051 (1982-06-01), Goodman
A. M. Goodman, "A Method for the Measurement of Short Minority Carrier Diffusion Lengths in Semiconductors," J. of Applied Physics, vol. 32, No. 12, pp. 2550-2552, Dec. 1961.
J. N. Shive, "Properties, Physics and Design of Semiconductor Devices," Van Nostrand, N.Y., 1959, p. 337.
R. Williams, "Schottky Barriers at the Interface Between Amorphous Silicon and Electrolytes," J. Applied Physics, 50 (4 Apr. 1979), pp. 2848-2851.
W. M. Latimer, Oxidation Potentials, Prentice Hall, 1952, Table 84, pp. 340-345.

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