M08200 - SEMI M82 - Test Method for the Carbon Acceptor Concentration in Semi-Insulating Gallium Arsenide Single Crystals by Infrared Absorption Spectroscopy
This Test Method covers the determination of the carbon content in GaAs using infrared (IR) absorption. The test method utilizes the linear relationship between the carbon content and the integrated absorption of the localized vibration of substitutionally bonded carbon (CAs). At a measurement temperature of 300 K (room temperature) this absorption band is observed at 580 cm−1, at 77 K between 582 and 583 cm−1.
This Test Method covers the determination of substitutional carbon mainly in SI single crystal GaAs. It may also be used for polycrystalline GaAs and conducting GaAs up to a free carrier concentration of about 1 × 1016 cm−3.
This Test Method is applicable for carbon content between 1 × 1013 cm−3 and the solubility limit (>1 × 1016 cm−3). The lower limit depends on the measurement temperature, the sample geometry and the quality of the spectrometer.
Measurement temperatures of both 300 K and 77 K may be used.
Advantages of the 300 K measurement are:
- the necessary spectral resolution is 1 cm-1 as compared to 0.1 cm-1 required at 77 K;
- cryostat is not necessary.
Advantages of the 77 K measurement are:
- sensitivity is higher (and therefore the detection limit lower);
- no reference sample with a low carbon content is necessary;
- commercial thin wafers can be measured.
The chemical carbon content in GaAs may be higher than the substitutional carbon content CAs as measured by this Standard. According to the present knowledge, however, state-of-the-art single crystal GaAs contains CAs only.
The document follows the roadmap laid out by SEMI M54, Guide for Semi-Insulating (SI) GaAs Material Parameters, defining the carbon concentration as an essential material parameter.
Referenced SEMI Standards (purchase separately)
SEMI M54 — Guide for Semi-Insulating (SI) GaAs Material Parameters
SEMI M64 — Test Method for the EL2 Deep Donor Concentration in Semi-Insulating (SI) Gallium Arsenide Single Crystals by Infrared Absorption Spectroscopy
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