US4393348A
Expired / Lapsed
US
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Method and apparatus for determining minority carrier diffusion length in semiconductors
Assignee: RCA Corp
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Filing: 1981-01-26
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Granted: 1983-07-12
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Expires: 2001-01-26
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. An unmodulated illumination 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. A vibrating Kelvin method-type probe electrode couples the SPV to a measurement system. The operating optical wavelength of an adjustable monochromator to compensate for the wavelength dependent sensitivity of a photodetector is selected to measure the illumination intensity (photon flux) on the silicon. Measurements of the relative photon flux for a plurality of wavelengths are plotted against the reciprocal of the optical absorption coefficient of the material. A linear plot of the data points is extrapolated to zero intensity. The negative intercept value on the reciprocal optical coefficient axis of the extrapolated linear plot is the diffusion length of the minority carriers.
Inventors
- 👤 Bernard Goldstein
- 👤 Joseph Dresner
- 👤 Daniel J. Szostak
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 18:40
CPC Classifications
G; G01; G01R; G01R31/00; G01R31/26; G01R31/265; G01R31/2656; Y; Y10; Y10S; Y10S136/00; Y10S136/29
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
133 words
An 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) means for illuminating a portion of the one major surface of the sample with steady d.c. monochromatic light that is of a selected wavelength to provide a d.c. surface photovoltage (d.c. SPV); (b) vibrating means positioned adjacent said illuminated surface for providing an alternating electrical signal representing said d.c. SPV on the sample; (c) electronic servo means responsive to said alternating electrical signal for automatically providing a nulling potential equal to said d.c. SPV; and (d) means for providing a signal representing the illumination incident upon the sample by detecting a portion of said illuminating light.
Claim 2
Independent Claim
133 words
An 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) means for illuminating a portion of the one major surface of the sample with steady d.c. monochromatic light that is of a selected wavelength to provide a d.c. surface photovoltage (d.c. SPV); (b) vibrating means positioned adjacent said illuminated surface for providing an alternating electrical signal representing said d.c. SPV on the sample; (c) electronic servo means responsive to said alternating electrical signal for automatically providing a nulling potential equal to said d.c. SPV; and (d) means for providing a signal representing the illumination incident upon the sample by detecting a portion of said illuminating light.
Claim 3
Dependent Claim
28 words
The apparatus according to claim 1, wherein said semiconductor material is amorphous silicon and wherein said light has a wavelength within the range of 4000 to 7000 angstroms.
Claim 4
Dependent Claim
33 words
The apparatus according to claim 1, wherein said modulated electrical signal means includes a probe having capacitance and arranged to vibrate over said illuminated surface to provide an alternating signal representing said SPV.
Claim 5
Dependent Claim
44 words
The apparatus of claim 1, wherein said modulated electrical signal means includes a Kelvin method-type probe positioned over said illuminated surface area and arranged to vibrate at a frequency within the range of about 10-10,000 Hz to provide an alternating signal representing the SPV.
Claim 6
Independent Claim
49 words
The apparatus of claims 3 or 4, wherein said nulling means is included in a servo loop for automatically adjusting the intensity of the illuminating means at a given wavelength to generate said SPV to a substantially constant value, and means to indicate the intensity of said illuminating light.
Claim 7
Independent Claim
130 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) illuminating a portion of the one major surface of the same with steady d.c. monochromatic light that is of a selected wavelength to provide a d.c. surface photovoltage (d.c. SPV); (b) vibrating a probe adjacent said illuminated surface to provide an alternating signal representing said d.c. SPV; (c) providing in an electronic servo means a nulling potential equal to said d.c. SPV in response to said alternating electric signal; and (d) providing a signal representing the illuminating intensity incident upon the sample by detecting a portion of said illuminating light.
Claim 8
Independent Claim
130 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) illuminating a portion of the one major surface of the same with steady d.c. monochromatic light that is of a selected wavelength to provide a d.c. surface photovoltage (d.c. SPV); (b) vibrating a probe adjacent said illuminated surface to provide an alternating signal representing said d.c. SPV; (c) providing in an electronic servo means a nulling potential equal to said d.c. SPV in response to said alternating electric signal; and (d) providing a signal representing the illuminating intensity incident upon the sample by detecting a portion of said illuminating light.
Claim 9
Dependent Claim
54 words
A method according to claim 6, wherein the representative SPV signal is provided by positioning in the path of the light a transparent capactive pickup electrode spaced from the illuminated surface of the sample, vibrating the electrode over the surface, an alternating signal representing the SPV appearing between the transparent electrode and the surface.
Claim 10
Dependent Claim
18 words
A method according to claim 6, comprising the step of selecting the wavelength of light with a monochromator.
Claim 11
Dependent Claim
25 words
A method according to claim 6, including the step of adjusting the intensity of the illuminating light to generate a predetermined magnitude of SPV signal.
Claim 12
Dependent Claim
50 words
A method according to claim 9, further including the step of automatically adjusting the intensity of the illuminating light at a given wavelength in an electronic servo loop in response to the SPV generated on the illuminated surface of the sample to maintain the SPV to a substantially constant value.
Claim 13
Dependent Claim
49 words
A method according to claim 10, further including the step of providing in the servo loop a control signal having a magnitude and polarity to compensate for changes in the SPV signal from a predetermined value, and using the control voltage to control the intensity of the illuminating light.
Claim 14
Dependent Claim
33 words
A method according to claim 6, further including the step of detecting a portion of the light at a given wavelength to generate an electrical signal representing the photon flux illuminating the sample.
Claim 15
Dependent Claim
32 words
A method according to claim 12, further including the step of compensating at each selected wavelength of the illuminating monochromatic light for the response characteristic of the detector that is wavelength dependent.
References Cited (Backward Citations)
US4333051A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1986-07-11 | 1987-01-10 | 1987-07-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-07-11 | 1991-01-10 | 1991-07-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-07-11 | 1995-01-10 | 1995-07-12 | $7700.00 | Window Closed / Lapsed |