ASTM F28-91(1997)

Standard Test Methods for Minority-Carrier Lifetime in Bulk Germanium and Silicon by Measurement of Photoconductivity Decay

SCOPE
1.1 These test methods cover the measurement of minority carrier lifetime appropriate to carrier recombination processes in bulk specimens of extrinsic single-crystal germanium or silicon.
1.2 These test methods are based on the measurement of the decay of the specimen conductivity after generation of carriers with a light pulse. The following two test methods are described:
1.2.1 Test Method A -Pulsed Light Method, that is suitable for both silicon and germination.  
1.2.2 Test Method B -Chopped Light Method, that is specific to silicon specimens with resistivity [>=]1 [omega][dot]cm.  
1.3 Both test methods are nondestructive in the sense that the specimens can be used repeatedly to carry out the measurement, but these methods require special bar-shaped test specimens of size (see Table 1) and surface condition (lapped) that would be generally unsuitable for other applications.
1.4 The shortest measurable lifetime values are determined by the turn-off characteristics of the light source while the longest values are determined primarily by the size of the test specimen (see Table 2).  Note 1-Minority carrier lifetime may also be deduced from the diffusion length as measured by the surface photovoltage (SPV) method made in accordance with Test Methods F391. The minority carrier lifetime is the square of the diffusion length divided by the minority carrier diffusion constant which can be calculated from the drift mobility. SPV measurements are sensitive primarily to the minority carriers; the contribution from majority carriers is minimized by the use of a surface depletion region. As a result lifetimes measured by the SPV method are often shorter than lifetimes measured by the photoconductivity decay (PCD) method because the photoconductivity can contain contributions from majority as well as minority carriers. In the absence of carrier trapping, both the SPV and PCD methods should yield the same values of lifetime (1)  providing that the correct values of absorption coefficient are used for the SPV measurements and that the contributions from surface recombination are properly accounted for in the PCD measurement.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazard statements are given in Section 9.

General Information

• Status: Historical
• Publication Date: 09-Jun-1997
• ICS: 29.045 - Semiconducting materials
• Technical Committee: F01 - Electronics

Relations

• Replaced By: ASTM F28-02 - Standard Test Methods for Minority-Carrier Lifetime in Bulk Germanium and Silicon by Measurement of Photoconductivity Decay (Withdrawn 2003)
• Effective Date: 10-Dec-2002

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact
ASTM International (www.astm.org) for the latest information.
Designation: F 28 – 91 (Reapproved 1997)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Methods for
Minority-Carrier Lifetime in Bulk Germanium and Silicon by
1
Measurement of Photoconductivity Decay
This standard is issued under the fixed designation F 28; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
TABLE 1 Dimensions of Three Recommended Bar-Shaped
1. Scope
Specimens
1.1 These test methods cover the measurement of minority
Type Length, mm Width, mm Thickness, mm
carrier lifetime appropriate to carrier recombination processes
A 15.0 2.5 2.5
in bulk specimens of extrinsic single-crystal germanium or
B 25.0 5.0 5.0
silicon.
C 25.0 10.0 10.0
1.2 These test methods are based on the measurement of the
decay of the specimen conductivity after generation of carriers
TABLE 2 Maximum Measurable Values of Bulk Minority Carrier
with a light pulse. The following two test methods are
Lifetime, t ,μs
B
described:
Material Type A Type B Type C
1.2.1 Test Method A—Pulsed Light Method, that is suitable
p-type germanium 32 125 460
2
for both silicon and germination.
n-type germanium 64 250 950
1.2.2 Test Method B—Chopped Light Method, that is spe-
p-type silicon 90 350 1300
3
n-type silicon 240 1000 3800
cific to silicon specimens with resistivity $1 V·cm.
1.3 Both test methods are nondestructive in the sense that
4
the specimens can be used repeatedly to carry out the mea-
lifetime (1) providing that the correct values of absorption coefficient are
surement, but these methods require special bar-shaped test
used for the SPV measurements and that the contributions from surface
recombination are properly accounted for in the PCD measurement.
specimens of size (see Table 1) and surface condition (lapped)
that would be generally unsuitable for other applications.
1.5 This standard does not purport to address all of the
1.4 The shortest measurable lifetime values are determined
safety concerns, if any, associated with its use. It is the
by the turn-off characteristics of the light source while the
responsibility of the user of this standard to establish appro-
longest values are determined primarily by the size of the test
priate safety and health practices and determine the applica-
specimen (see Table 2).
bility of regulatory limitations prior to use. Specific hazard
statements are given in Section 9.
NOTE 1—Minority carrier lifetime may also be deduced from the
diffusion length as measured by the surface photovoltage (SPV) method
2. Referenced Documents
made in accordance with Test Methods F 391. The minority carrier
lifetime is the square of the diffusion length divided by the minority carrier
2.1 ASTM Standards:
diffusion constant which can be calculated from the drift mobility. SPV
D 1125 Test Method for Electrical Conductivity and Resis-
measurements are sensitive primarily to the minority carriers; the contri-
5
tivity of Water
bution from majority carriers is minimized by the use of a surface
F 42 Test Method for Conductivity Type of Extrinsic
depletion region. As a result lifetimes measured by the SPV method are
6
Semiconducting Materials
often shorter than lifetimes measured by the photoconductivity decay
(PCD) method because the photoconductivity can contain contributions F 43 Test Method for Resistivity of Semiconductor Materi-
6
from majority as well as minority carriers. In the absence of carrier
als
trapping, both the SPV and PCD methods should yield the same values of
F 391 Test Methods for Minority Carrier Diffusion Length
in Extrinsic Semiconductors by Measurement of Steady-
6
State Surface Photovoltage
1 2.2 Other Standards:
These test methods are under the jurisdiction of ASTM Committee F-1 on
DIN 50440/1 Measurement of Carrier Lifetime in Silicon
Electronicsand are the direct responsibility of Subcommittee F01.06 on Silicon
Materials and Process Control.
Single Crystals by Means of Photoconductive Decay:
Current edition approved Oct. 15, 1991. Published December 1991. Originally
3
Measurement on Bar-Shaped Test Specimens
published as F 28 – 63 T. Last previous edition F 28 – 90.
2
This test method is based in part on IEEE Standard 225, Proceedings IRE, Vol
49, 1961, pp. 1292–1299.
3 4
DIN 50440/1 is an equivalent test method. It is the responsibility of DIN The boldface numbers in parenthesis refer to a list of references at the end of
Committee NMP 221, with which Committee F-1 maintains close liaison. DIN these test methods.
5
50440/1, is available from Beuth Verlag Gmb
...