ASTM F391-96

1.1 These test methods 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.

1.2 These test methods are based on the measurement of surface photovoltage (SPV) as a function of energy (wavelength) of the incident illumination. The following two test methods are described:

1.2.1 Test Method A -Constant magnitude surface photovoltage (CMSPV) method.

1.2.2 Test Method B -Linear photovoltage, constant photon flux (LPVCPF) method.

1.3 Both test methods are nondestructive.

1.4 The limits of applicability with respect to specimen material, resistivity, and carrier lifetime have not been determined; however, measurements have been made on 0.1 to 50 [omega][dot]cm - and -type silicon specimens with carrier lifetimes as short as 2 ns.

1.5 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.

1.6 These test methods also have been applied to the determination of the width of the denuded zone in silicon wafers.

1.7 These test methods measure diffusion lengths at room temperature (22°C) only. Lifetime and diffusion length are a function of temperature.

1.8 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.