US5010294A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method for topically-resolved determination of the diffusion length of minority charge carriers in a semiconductor crystal body with the assistance of an electrolytic cell
Assignee: Siemens AG
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Filing: 1990-05-11
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Granted: 1991-04-23
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Expires: 2010-05-11
Abstract
Abstract The measurement of the diffusion length of minority charge carriers in a semiconductor crystal body is enabled in that the front side and the rear side of the crystal wafer are each respectively brought into contact with an electrolyte in a respective measuring cell and an inhibiting space charge zone is generated at the front side of the wafer. The front side is irradiated with light having a wave length of λ>800 nm and the front side photocurrent I 1 of the minority charge carriers thereby generated is measured. The diffusion length L can be calculated from the photocurrent I 1 with the assistance of a mathematical equation. The topical distribution of the diffusion length L is obtained given point-by-point irradiation and scanning over the crystal wafer. Diffusion lengths of L<150 μm can be measured by selecting a light source having a wave length of λ>800 nm.
Inventors
- 👤 Helmut Foell
- 👤 Volker Lehmann
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 22:07
CPC Classifications
G; G01; G01R; G01R31/00; G01R31/26; G01R31/265; G01R31/2656
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
187 words
A method for determining the diffusion length L of minority charge carriers in a semiconductor crystal body carrying an ohmic contact, comprising the steps of: applying a measuring cell having an electrode therein to one side of the semiconductor crystal body so that a first surface thereof is exposed to the interior of the measuring cell; filling the measuring cell with electrolyte so that the surface and the electrode are in contact with the electrolyte; applying a voltage between the electrode and the ohmic contact to produce an inhibiting space charge zone at the first surface of the semiconductor crystal body; irradiating the surface with light having a predetermined wavelength λ>800 nm to produce a photocurrent I 1 between the first surface and the electrode; measuring the photocurrent I 1 ; and determining the diffusion length L from the equation I.sub.1 /I.sub.1,max =(αL/(1+αL)) e.sup.-αw where α is the absorption coefficient for radiation having the predetermined wavelength λ, w is the expanse of the inhibiting space charge zone, and I 1 , max is a calibrated current obtained from a known specimen having an extremely long diffusion length.
Claim 2
Independent Claim
187 words
A method for determining the diffusion length L of minority charge carriers in a semiconductor crystal body carrying an ohmic contact, comprising the steps of: applying a measuring cell having an electrode therein to one side of the semiconductor crystal body so that a first surface thereof is exposed to the interior of the measuring cell; filling the measuring cell with electrolyte so that the surface and the electrode are in contact with the electrolyte; applying a voltage between the electrode and the ohmic contact to produce an inhibiting space charge zone at the first surface of the semiconductor crystal body; irradiating the surface with light having a predetermined wavelength λ>800 nm to produce a photocurrent I 1 between the first surface and the electrode; measuring the photocurrent I 1 ; and determining the diffusion length L from the equation I.sub.1 /I.sub.1,max =(αL/(1+αL)) e.sup.-αw where α is the absorption coefficient for radiation having the predetermined wavelength λ, w is the expanse of the inhibiting space charge zone, and I 1 , max is a calibrated current obtained from a known specimen having an extremely long diffusion length.
Claim 3
Dependent Claim
34 words
The method of claim 1, wherein the step of irradiating is further defined as: focusing light onto the first surface; and scanning the focused light across the first surface to obtain a topically-resolved determination.
Claim 4
Dependent Claim
22 words
The method of claim 2, wherein the step of irradiating is further defined as: focusing a laser beam on the first surface.
Claim 5
Dependent Claim
22 words
The method of claim 2, wherein the step of irradiating is further defined as: energizing a light-emitting diode to produce the light.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1994-04-22 | 1994-10-22 | 1995-04-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-04-22 | 1998-10-22 | 1999-04-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-04-22 | 2002-10-22 | 2003-04-23 | $7700.00 | Window Closed / Lapsed |