Infrared Photoluminescence Spectroscopy

Significance of the Topic

Photoluminescence spectroscopy in the infrared range is a powerful tool for characterizing semiconductor materials and devices. It enables detailed study of band structure, excitonic features, defect states and phonon interactions in bulk and heterostructured samples. Applications span from research on quantum wells and optoelectronic devices such as lasers and LEDs to quality control in silicon manufacturing.

Objectives and Study Overview

This application note presents Bruker’s infrared PL solutions based on Fourier-transform infrared (FT-IR) spectrometers (VERTEX, INVENIO R). It outlines the advantages of FT-IR technology, describes near-infrared (NIR) and mid-infrared (MIR) PL modules and illustrates performance through example measurements on quantum wells, solar cells and bulk semiconductors.

Methodology and Used Instrumentation

FT-IR PL exploits the Jaquinot (throughput) and Fellgett (multiplex) advantages to achieve high sensitivity, broad spectral range and adjustable resolution via mirror travel control. A precise interferometer laser ensures spectral accuracy. Two module types are described:

• PLII module for NIR and visible PL: attaches to VERTEX or INVENIO R, offers up to two cw excitation lasers (532 nm, 1064 nm), InGaAs detectors, optional Si avalanche diode for 500–1050 nm, glass or mirror objectives with video and XY mapping, room-temperature and cryogenic sample mounts.
• Vacuum PL module for MIR PL: integrates with VERTEX 80v in vacuum, supports modulated excitation, step-scan interferometer operation, lock-in detection, LN₂-cooled detectors (InSb, MCT) and cryostats or pulse-tube coolers to suppress atmospheric absorption and thermal background.

Main Results and Discussion

• NIR PL on InGaP solar cells and GaAs/AlGaInAs multiple quantum wells achieved high resolution (<0.06 cm⁻¹) and fast acquisition (<10 s) with clear detection of exciton and barrier emission down to ~0.006 nm spectral width.
• A liquid-helium-cooled cryostat enabled low-temperature PL at 10 K, revealing weak barrier peaks (~1/170 intensity) in multiple quantum wells without extended integration times.
• MIR PL of PbS bulk at room temperature was demonstrated using modulated 1064 nm excitation, step-scan and lock-in amplification. Vacuum operation eliminated atmospheric CO₂/H₂O features and suppressed 300 K background, yielding stable MIR spectra around 3–4 µm.
• Integrated beam paths and OPUS software switching support combined photoluminescence, reflectance and transmittance experiments, including photomodulated reflectance for band-structure studies.

Benefits and Practical Applications

• Enhanced sensitivity and resolution for semiconductor QC and R&D, even on weak or low‐temperature signals.
• Flexible configuration supports laboratories focusing on infrared measurements with occasional VIS PL needs, reducing system complexity.
• Vacuum PL modules enable challenging MIR applications in material research, energy materials and sensor development.

Future Trends and Opportunities

Advances in detector technology and laser modulation will further extend sensitivity into the far infrared. Integration of automated mapping, time-resolved PL and combined photoreflectance/PL workflows will open new avenues in quantum-material studies. Custom external excitation sources and lock-in schemes may enhance selectivity for ultralow-intensity emissions. Expansion into industrial in-line monitoring and AI-assisted spectral analysis will broaden adoption.

Conclusion

Bruker’s FT-IR-based photoluminescence systems deliver high throughput, broad spectral coverage and exceptional sensitivity from the visible to the mid infrared. Modular PLII and vacuum PL assemblies enable rapid NIR analysis and rigorous MIR measurements by overcoming atmospheric and thermal background challenges. These solutions support diverse applications in semiconductor research, optoelectronic device development and industrial quality control.

References

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