Emission Spectroscopy in the Mid-infrared using FTIR Spectrometry
Yong-Gang Zhang
DOI: 10.1117/3.1002245.ch26
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Excerpt

Emission spectroscopy, including the photoluminescence (PL) spectrum, the electroluminescence (EL) spectrum, and lasing spectra (LS), has become a useful tool in the scientific research and industry development of semiconductor optoelectronic materials and devices. Among different spectroscopy schemes, Fourier transform infrared (FTIR) spectrometers are widely used, especially in the mid-infrared (MIR) band. Through a simple review of FTIR and detailed analysis of its merits and limitations in emission spectroscopy, an improved FTIR spectroscopy system adopting a simple, convenient, and universal emission accessory attached to a commercial FTIR spectrometer with a diode-pumped solid state (DPSS) laser for PL is introduced in this chapter. Based on this system, three different FTIR spectroscopy modes, rapid scan (RS), double modulation (DM), and step scan (SS), are adequately demonstrated on various PL, EL, and LS samples.

The FTIR spectrometer, which is based on a Michelson interferometer adopting a beam spliter with a light source, moving mirror, fixed mirror, and photodetector on four opposite arms, is a mature and powerful tool used in numerous fields to distinguish diversified features of materials and devices. While dispersive spectroscopy uses a prism or grating to differentiate the wavelengths of light in an actual spectrum, in FTIR, only an interferogram is acquired, from which a virtual spectrum is then gained by using a Fourier transform algorithm. Compared to a dispersive spectrometer, the high flux, low equivalent noise, fast scan speed, and parallel beam features of FTIR spectroscopy make it an optimal option, especially in the MIR or far-infrared (FIR) bands, although in certain cases some artifacts in the measurement might exist. Starting in the mid-1900s, these features have contributed to the multiplexing (Fellgett) and throughput (Jacquinot) advantages of FTIR. Since then, FTIR instrumentation has evolved to include computer technology for fast Fourier transforms. Because of high demand, commercial FTIR spectrometers are mainly designed for obtaining absorption or reflection measurements using an internal polychromatic infrared radiation source, with the specimen mounted into the sample compartment inside the spectrometer.

© 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)

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