Infrared Photoluminescence Spectroscopy

Significance of the Topic

Photoluminescence (PL) spectroscopy in the infrared region is a cornerstone technique for characterizing semiconductor materials and optoelectronic devices such as lasers, LEDs, sensors, and photovoltaic cells. By probing radiative recombination processes, PL reveals critical information on band structure, excitonic behavior, sample quality and phonon interactions across heterostructures (quantum wells, MQWs) and bulk specimens.

Objectives and Overview of the Study

This application note presents Bruker’s infrared PL solutions based on FT-IR technology using the VERTEX and INVENIO R spectrometers. It outlines advantages of FT-IR spectroscopy, describes NIR, VIS/UV and MIR PL modules, and illustrates measurement strategies, instrumental configurations and representative spectra for both room-temperature and cryogenic measurements.

Methodology and Approach

FT-IR PL leverages two main advantages over dispersive techniques:

• Throughput (Jaquinot) advantage for higher sensitivity.
• Multiplex (Fellgett) advantage enabling high resolution across broad spectral ranges.

Spectral resolution is controlled via mirror travel in the interferometer, and accuracy is ensured by an internal reference laser.
Continuous-wave excitation lasers (commonly 532 nm and 1064 nm) deliver ~100 mW power; optional customer lasers may be integrated. Detectors include InGaAs (NIR), Si avalanche diodes (VIS), Ge (ultralow noise NIR) and liquid-nitrogen cooled InSb (MIR). For MIR PL, step-scan operation with lock-in detection and laser modulation suppresses thermal background and atmospheric artifacts; vacuum beam paths eliminate water/CO₂ absorptions.

Instrumentation

Key hardware and software components include:

• VERTEX 80 / 80v and INVENIO R FT-IR spectrometers
• PLII module for NIR/VIS PL with integrated sample compartment and optional mirror objective mapping stage
• Vacuum PL module for MIR PL with external cryostats (liquid He/N₂ or pulse tube), chopper wheel and lock-in interface
• CW excitation lasers (532 nm, 1064 nm) and optical filters
• Detectors: high-gain InGaAs, Si avalanche diode, Ge, and LN₂-cooled InSb
• Beam splitters for NIR/VIS/UV and MIR ranges; OPUS software for mode switching (PL, reflectance, transmittance, photomodulated reflectance)

Main Results and Discussion

- NIR PL spectra of GaAs bulk and various MQWs acquired within seconds, resolving excitonic peaks and barrier emissions at low temperature.
- InGaP solar cell PL in the visible (~690 nm) and GaAs substrate emission (~890 nm) demonstrated with high spectral resolution (<0.024 nm).
- Room-temperature MIR PL of PbS bulk at ~2.5–4 µm achieved via modulated 1064 nm excitation, step-scan FT-IR and lock-in detection, effectively eliminating 300 K background.
- Photomodulated reflectance measurements facilitated by dual beam paths, enabling band-structure investigations with step-scan amplitude modulation.

Benefits and Practical Applications

Bruker’s FT-IR PL systems deliver:

• Exceptional sensitivity and spectral resolution without manual grating exchange.
• Broad spectral coverage from VIS/UV through MIR in one instrument.
• Flexible sample handling with cryogenic and room-temperature options.
• Rapid data acquisition for high-throughput QA/QC and research.
• Integration of PL, reflectance, transmittance and photomodulated methods in a single software environment.

Future Trends and Possibilities

Emerging developments include:

• Next-generation detectors with extended sensitivity into the far IR.
• Cryogen-free cooling solutions for simplified low-temperature operation.
• Integration with time-resolved and ultrafast PL techniques.
• Expansion to novel materials (e.g., 2D semiconductors, perovskites) and advanced device architectures.
• Enhanced automation and mapping for spatially resolved PL characterization.

Conclusion

FT-IR-based infrared photoluminescence spectroscopy using Bruker’s VERTEX/INVENIO R platforms and dedicated PL modules provides a versatile, high-sensitivity toolset for semiconductor and optoelectronic research and quality control. From rapid NIR measurements to sophisticated MIR and photomodulated experiments under vacuum, these systems offer comprehensive analytical capabilities in a unified workflow.

References

1. P.R. Griffiths, Fourier Transform Infrared Spectroscopy, 2nd ed., Wiley-Interscience, 2007.
2. T. Gründl et al., GaInAsN growth studies for InP-based long-wavelength laser applications, Journal of Crystal Growth 311 (2009) 1719–1722.
3. A. Jaffrès et al., Photon management in La2BaZnO5: Tm3+/Yb3+ and La2BaZnO5:Pr3+/Yb3+ by two-step cross-relaxation, Chem. Phys. Lett. 527 (2012) 42–46.
4. S. Sauvage et al., Midinfrared unipolar photoluminescence in InAs/GaAs quantum dots, Phys. Rev. B 60 (1999) 15589–15592.
5. J. Shao et al., Modulated photoluminescence spectroscopy with a step-scan FT-IR spectrometer, Rev. Sci. Instrum. 77 (2006).
6. C.J. Manning and P.R. Griffiths, Noise Sources in FT-IR Spectrometry, Appl. Spectrosc. 51 (1997) 1092–1101.
7. M. Motyka, Fourier Transformed Photoreflectance and Photoluminescence of Mid Infrared GaSb-Based Type II Quantum Wells, Appl. Phys. Express 2 (2009) 126505.
8. D. Stange et al., Optical Transitions in Direct-Bandgap Ge1−xSnx Alloys, ACS Photonics (2015).
9. T.J.C. Hosea et al., A new FT-modulation technique for narrow band-gap materials in the mid- to far-IR, Phys. Status Solidi (a) 202 (2005) 1233–1243.
10. Ma Li-Li et al., Spectral Resolution Effects on the Lineshape of Photoreflectance, J. Appl. Phys. 28 (2011) 047801.