US4454472A
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Method and apparatus for determining minority carrier diffusion length in semiconductors
Assignee: RCA Corp
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Filing: 1982-02-19
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Granted: 1984-06-12
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Expires: 2002-02-19
Abstract
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 drop of a transparent 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 drop of redox couple solution functions to create a liquid Schottky barrier at the surface of the material. Illumination light is passed through a transparent rod supported over the surface and through the drop of transparent electrolyte. The drop is held in the gap between the rod and the surface. Steady red light is also used as an optical bias to reduce deleterious space-charge effects that occur in amorphous silicon.
Inventors
- 👤 Arnold R. Moore
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 14:39
CPC Classifications
G; G01; G01R; G01R31/00; G01R31/28; G01R31/282; G01R31/2831; Y; Y10; Y10S; Y10S136/00; Y10S136/29; Y10S204/00; Y10S204/06
Claims Analysis
Total Claims: 36
Claim 1
Independent Claim
223 words
A method for determining the minority carrier diffusion length of a sample of semiconductor material, the sample having two major surfaces, one of the surfaces arranged for illumination and the other surface shielded from illumination including the steps of: (a) providing on a portion of the one major surface of the sample a substantially transparent drop of an electrolyte solution having sufficient surface tension to sustain said drop on said surface and containing redox couples, said electrolyte solution being soluble, stable and non-reactive to the semiconductor material and free of solid or gaseous products and having a redox potential to form a liquid Schottky barrier at the surface of the sample; (b) holding said drop on said surface portion beneath a body of transparent material; (c) substantially illuminating said portion of the one major surface of the sample with monochromatic light that is of a selected wavelength by passing said light through said transparent conducting surface and said drop of redox couple solution to provide at said conducting surface an electrical signal representing the surface photovoltage (SPV) on the sample generated in response to said light; (d) controlling the SPV electrical signal to a predetermined value; and (e) providing a first electrical signal representing the illuminating intensity (I) incident upon the sample, and a second electrical signal representing the wavelength of the light.
Claim 2
Independent Claim
223 words
A method for determining the minority carrier diffusion length of a sample of semiconductor material, the sample having two major surfaces, one of the surfaces arranged for illumination and the other surface shielded from illumination including the steps of: (a) providing on a portion of the one major surface of the sample a substantially transparent drop of an electrolyte solution having sufficient surface tension to sustain said drop on said surface and containing redox couples, said electrolyte solution being soluble, stable and non-reactive to the semiconductor material and free of solid or gaseous products and having a redox potential to form a liquid Schottky barrier at the surface of the sample; (b) holding said drop on said surface portion beneath a body of transparent material; (c) substantially illuminating said portion of the one major surface of the sample with monochromatic light that is of a selected wavelength by passing said light through said transparent conducting surface and said drop of redox couple solution to provide at said conducting surface an electrical signal representing the surface photovoltage (SPV) on the sample generated in response to said light; (d) controlling the SPV electrical signal to a predetermined value; and (e) providing a first electrical signal representing the illuminating intensity (I) incident upon the sample, and a second electrical signal representing the wavelength of the light.
Claim 3
Dependent Claim
22 words
The method of claim 1 wherein said redox couple has a redox (oxidation-reduction) potential in the range of 0.6 to -1.65 volts.
Claim 4
Dependent Claim
26 words
The method of claim 2 wherein said material is amorphous silicon and the light is at a wavelength within the range of 4,000 to 7,000 angstroms.
Claim 5
Dependent Claim
33 words
The method of claim 3 wherein the redox couple solution comprises a stannous/stannic (Sn +2 /Sn +4 ) couple in an acid solution in which the standard electrode potential E is -0.15 volts.
Claim 6
Dependent Claim
35 words
The method of claim 3 wherein the redox couple solution comprises a ferrocyanide/ferricyanide [Fe(CN) 6 -3 /Fe(CN) 6 -4 ] couple in an acid solution in which the standard electrode potential (E) is -0.36 volts.
Claim 7
Dependent Claim
33 words
The method of claim 3 wherein the redox couple solution comprises a ferrous/ferric (Fe +2 /Fe +3 ) couple in an acid solution in which the standard electrode potential (E) is -0.77 volts.
Claim 8
Dependent Claim
32 words
The method of claim 3 wherein the redox couple solution comprises a cerrous/cerric (Ce +3 /Ce +4 ) couple in an acid solution in which the electrical potential (E) is -1.61 volts.
Claim 9
Dependent Claim
40 words
The method of claim 3 wherein the redox couple solution comprises a hydroquinone/quinone couple [C 6 H 4 (OH) 2 /C 6 H 4 O 2 ] in standard buffered solution in which the electrical potential (E) is about -0.7+0.059×pH.
Claim 10
Dependent Claim
23 words
The method of claim 1 further comprising the step of: moving said drop over said material surface from one portion thereof to another.
Claim 11
Dependent Claim
37 words
The method of claim 1 further comprising the step of: varying a vertical force on said drop to deform the drop to a selected vertical thickness to thereby alter the effective transparency and conductivity of the drop.
Claim 12
Dependent Claim
27 words
The method of claim 1 further comprising the step of illuminating said one major surface with steady red light to suppress space charge effects in said sample.
Claim 13
Dependent Claim
36 words
The method of claim 1 comprising the step of automatically plotting a curve of illuminating intensity (I) versus the reciprocal absorption coefficient (α) as a function of wavelength (λ) for a plurality of wavelengths of light.
Claim 14
Dependent Claim
13 words
The method of claim 1 comprising illuminating the sample with steady monochromatic light.
Claim 15
Dependent Claim
13 words
The method of claim 1 comprising illuminating the sample with chopped monochromatic light.
Claim 16
Dependent Claim
218 words
Apparatus for determining the minority carrier diffusion length of a sample of semiconductor material, the sample having two major surfaces, one of the surfaces arranged for illumination and the other surface shielded from illumination comprising: (a) on a portion of the one major surface, a substantially transparent drop of an electrolyte solution having sufficient surface tension to sustain said drop on said surface and containing redox couples, said electrolyte solution being soluble, stable and non-reactive to the semiconductor material and free of solid or gaseous products; (b) a body of transparent material having a conductive transparent surface portion supported over said material surface portion and means to hold said drop of redox solution on said material surface portion; (c) means for illuminating said portion of the one major surface of the sample with monochromatic light that is of a selected wavelength by passing said light through said body, said transparent surface and said drop of redox couple solution to provide an electrical signal representing the surface photovoltage (SPV) on the sample generated in response to said light; (d) means for controlling the SPV electrical signal to a predetermined value; and (e) means for providing a first electrical signal representing the illuminating intensity (I) incident upon the sample, and a second electrical signal representing the wavelength of the light.
Claim 17
Dependent Claim
218 words
Apparatus for determining the minority carrier diffusion length of a sample of semiconductor material, the sample having two major surfaces, one of the surfaces arranged for illumination and the other surface shielded from illumination comprising: (a) on a portion of the one major surface, a substantially transparent drop of an electrolyte solution having sufficient surface tension to sustain said drop on said surface and containing redox couples, said electrolyte solution being soluble, stable and non-reactive to the semiconductor material and free of solid or gaseous products; (b) a body of transparent material having a conductive transparent surface portion supported over said material surface portion and means to hold said drop of redox solution on said material surface portion; (c) means for illuminating said portion of the one major surface of the sample with monochromatic light that is of a selected wavelength by passing said light through said body, said transparent surface and said drop of redox couple solution to provide an electrical signal representing the surface photovoltage (SPV) on the sample generated in response to said light; (d) means for controlling the SPV electrical signal to a predetermined value; and (e) means for providing a first electrical signal representing the illuminating intensity (I) incident upon the sample, and a second electrical signal representing the wavelength of the light.
Claim 18
Dependent Claim
23 words
The apparatus according to claim 15 wherein said redox couple has a redox (oxidation-reduction) potential in the range of 0.6 to -1.65 volts.
Claim 19
Dependent Claim
28 words
The apparatus according to claim 16 wherein said semiconductor material is amorphous silicon and wherein said light has a wavelength within the range of 4000 to 7000 angstroms.
Claim 20
Dependent Claim
33 words
The apparatus according to claim 16 wherein the redox couple solution comprises a stannous/stannic (Sn +2 /Sn +4 ) couple in an acid solution in which the electrical potential (E) is -0.15 volts.
Claim 21
Dependent Claim
35 words
The apparatus according to claim 16 wherein the redox couple solution comprises a ferrocyanide/ferricyanide [Fe(CN) 6 -4 Fe(CN) 6 -3 ] couple in an acid solution in which the electrical potential (E) is -0.36 volts.
Claim 22
Dependent Claim
33 words
The apparatus according to claim 16 wherein the redox couple solution comprises a ferrous/ferric (Fe +2 /Fe +3 ) couple in an acid solution in which the electrical potential (E) is -0.77 volts.
Claim 23
Dependent Claim
33 words
The apparatus according to claim 16 wherein the redox couple solution comprises a cerrous/cerric (Ce +3 /Ce +4 ) couple in an acid solution in which the electrical potential (E) is -1.61 volts.
Claim 24
Dependent Claim
42 words
The apparatus according to claim 16 wherein the redox couple solution comprises a hydraquinone/quinone couple (C 6 H 4 (OH) 2 /C 6 H 4 O 2 ) couple in an acid solution in which the electrical potential (E) is about -0.7+0.059×pH.
Claim 25
Dependent Claim
28 words
The apparatus according to claim 15 further including means for illuminating said major one surface portion with steady red light to suppress space charge effects in said sample.
Claim 26
Dependent Claim
45 words
The apparatus according to claim 15 further including plotting means responsive to said first and second signals for automatically plotting a curve of illuminating intensity (I) versus the reciprocal absorption coefficient (α) as a function of wavelength (λ) for a plurality of wavelengths of light.
Claim 27
Dependent Claim
31 words
The apparatus according to claim 15 wherein said sample is formed of N-type amorphous silicon semiconductor material and wherein said redox solution has a redox potential of +0.1 to -1.65 volts.
Claim 28
Dependent Claim
31 words
The apparatus according to claim 15 wherein said sample is formed of P-type amorphous silicon semiconductor material and wherein said redox solution has a redox potential of +0.6 to +0.1 volts.
Claim 29
Dependent Claim
24 words
The apparatus according to claim 15 wherein said electrical signal means includes a high impedance amplifier to reduce the current drawn through said solution.
Claim 30
Dependent Claim
15 words
The apparatus according to claim 15 wherein said illuminating means includes a xenon light source.
Claim 31
Dependent Claim
21 words
The apparatus according to claim 28 further including variably adjustable attenuator means to attenuate light intensity from said xenon light source.
Claim 32
Dependent Claim
34 words
The apparatus according to claim 29 further including servo means responsive to said SPV signal to automatically adjust said attenuator to control the light intensity from said xenon light source to a predetermined value.
Claim 33
Dependent Claim
27 words
The apparatus according to claim 15 wherein said drop holding means includes means to move said drop over said material surface from one portion thereof to another.
Claim 34
Dependent Claim
21 words
The apparatus according to claim 15 wherein said drop hold means includes means to vary a vertical force on said body.
Claim 35
Dependent Claim
53 words
The apparatus according to claim 15 wherein said transparent body is an elongated fiber optic rod having one end coupled to receive light from said illuminating means and wherein said SPV signal means includes a conductive ring around the opposite end of said rod and adapted to mate electrical contact with said drop.
Claim 36
Dependent Claim
50 words
The apparatus according to claim 33 wherein said rod has a second end adjacent said one end, said second end adapted to be coupled to a source of red d.c. light whereby red d.c. light and a.c. illuminating light is conducted through said rod to said surface via said drop.
References Cited (Backward Citations)
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