Minority carrier lifetime is one of the essential characteristics of semiconductor materials. Many metallic impurities form recombination centers in germanium and silicon; in many cases, these recombination centers are deleterious to device and circuit performance. In other cases, the recombination characteristics must be carefully controlled to obtain the desired device performance.

If the free carrier density is not too high, minority carrier lifetime is controlled by such recombination centers; however, because it does not distinguish the type of center present, a measurement of minority carrier lifetime provides only a nonspecific, qualitative test for metallic contamination in the material.

When present in sufficient quantity, free carriers control the lifetime; thus, these test methods do not provide a reliable means for establishing the presence of recombination centers due to unwanted metallic or other non-dopant impurities when applied to silicon specimens with resistivity below 1 Ω·cm.

This Test Method is suitable for use in research, development, and process control applications; it is not suitable for acceptance testing of polished wafers since it cannot be performed on specimens with polished surfaces.

This Test Method covers the measurement of minority carrier lifetime appropriate to carrier recombination processes in bulk specimens of extrinsic single-crystal germanium or silicon.

The following two test methods are described:

• Test Method A — Pulsed Light Method, this is suitable for both silicon and germanium.
• Test Method B — Chopped Light Method, that is specific to silicon specimens with resistivity ≥1 Ω·cm.

Referenced SEMI Standards (purchase separately)
SEMI M59 — Terminology for Silicon Technology
SEMI MF42 — Test Method for Conductivity Type of Extrinsic Semiconducting Materials
SEMI MF43 — Test Method for Resistivity of Semiconductor Materials
SEMI MF391 — Test Method for Minority Carrier Diffusion Length in Extrinsic Semiconductors by Measurement of Steady-State Surface Photovoltage
SEMI MF1535 — Test Method for Carrier Recombination Lifetime in Silicon Wafers by Noncontact Measurement of Photoconductivity Decay by Microwave Reflectance

Revision History
SEMI MF28-0317E (Reapproved 0622)
SEMI MF28-0317E (editorial revision)
SEMI MF28-0317 (technical revision)
SEMI MF28-0707 (Reapproved 0912)
SEMI MF28-0707 (technical revision)
SEMI MF28-1106 (technical revision)
SEMI MF28-02 (first SEMI publication)