MF039100 - SEMI MF391 - Test Method for Minority Carrier Diffusion Length in Extrinsic Semiconductors by Measurement of Steady-State Surface Photovoltage
This Standard was technically approved by the Silicon Wafer Global Technical Committee. This edition was approved for publication by the global Audits and Reviews Subcommittee on December 16, 2009. Available at www.semi.org in February 2010; originally published by ASTM International as ASTM F391-73T; previously published July 2008.
E This Standard was editorially modified in November 2017. A change was made to correct a nonconforming title per the Procedure Manual, Appendix 4.
Minority carrier lifetime is one of the essential characteristics of semiconductor materials. In epitaxial layers and in thin single crystal wafers, the surface recombination corrections necessary to derive the minority carrier lifetime from the photoconductive decay (PCD) method covered by SEMI MF28 and SEMI MF1535 are excessively large.
Therefore, other test methods are required to cover the measurement of minority carrier diffusion lengths in specimens of extrinsic single-crystal semiconducting materials or in homoepitaxial layers of known resistivity deposited on more heavily doped substrates of the same type, provided that the thickness of the specimen or layer is greater than four times the diffusion length. Three test methods are described:
•Test Method A — Constant magnitude surface photovoltage (CMSPV) method. This test method circumvents the influence of surface recombination on the lifetime measurement by maintaining constant front surface conditions.
•Test Method B — Linear photovoltage, constant photon flux (LPVCPF) method. This test method utilizes only conditions and data points that are not influenced by surface recombination and other non-linear effects.
•Test Method C — Digital oscilloscope recording (DOR) method. This test method provides the direct control of relaxation processes of surface photovoltage (SPV) appearance and disappearance on minimum radiation intensity and eliminates any non-linear and other distorting effects, which is feasible on these conditions.
These test methods are suitable for use in research, process control, and materials acceptance.
These test methods are particularly useful in testing materials to be used in photovoltaic cells and other optical device applications since the diffusion length is derived by methods that are closely related to the functioning of the device.
These test methods are based on the measurement of surface photovoltage (SPV) as a function of energy (wavelength) of the incident illumination.
All three test methods covered are nondestructive. The limits of applicability with respect to specimen material, resistivity, and carrier lifetime have not been determined; however, measurements have been made on 0.01 to 50 Ω·cm n- and p-type silicon specimens with carrier lifetimes as short as 2 ns.
These test methods were developed for use on single crystal specimens of silicon. They may also be used to measure an effective diffusion length in specimens of other semiconductors such as gallium arsenide (with suitable adjustment of the wavelength (energy) range of the illumination and specimen preparation procedures) and an average effective diffusion length in specimens of polysilicon in which the grain boundaries are normal to the surface.
These test methods also have been applied to the determination of the width of the denuded zone in silicon wafers.
These test methods measure diffusion lengths at room temperature (22°C) only. Lifetime and diffusion length are a function of temperature.
Referenced SEMI Standards
SEMI C23 — Specifications for Buffered Oxide Etchants
SEMI C30 — Specifications for Hydrogen Peroxide
SEMI C34 — Specification and Guide for Mixed Acid Etchants
SEMI M59 — Terminology for Silicon Technology
SEMI MF28 — Test Method for Minority Carrier Lifetime in Bulk Germanium and Silicon by Measurement of Photoconductivity Decay
SEMI MF84 — Test Method for Measuring Resistivity of Silicon Wafers with an In-Line Four-Point Probe
SEMI MF95 — Test Method for Thickness of Lightly Doped Silicon Epitaxial Layers on Heavily Doped Silicon Substrates Using an Infrared Dispersive Spectrophotometer
SEMI MF110 — Test Method for Thickness of Epitaxial or Diffused Layers in Silicon by the Angle Lapping and Staining Technique
SEMI MF533 — Test Method for Thickness and Thickness Variation of Silicon Wafers
SEMI MF673 — Test Method for Measuring Resistivity of Semiconductor Slices or Sheet Resistance of Semiconductor Films with a Noncontact Eddy-Current Gauge
SEMI MF1535 — Test Method for Carrier Recombination Lifetime in Silicon Wafers by Non-Contact Measurement of Photoconductivity Decay by Microwave Reflectance
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