Revisiting the Fabry-Perot reflectivity method for mid-infrared optical index measurement: case study of InGaAs,...

Area of Science:

• Optics and Photonics
• Materials Science
• Semiconductor Physics

Background:

• Accurate optical characterization is crucial for semiconductor devices like quantum cascade lasers.
• Existing methods for measuring optical indices can be complex or require specialized equipment.
• The mid-infrared spectrum is vital for applications such as gas sensing and free-space communications.

Purpose of the Study:

• To revisit and validate the Fabry-Perot (FP) reflectivity method for measuring optical indices.
• To demonstrate the method's applicability using standard Fourier transform infrared (FTIR) spectrometers.
• To provide precise optical index data for key quantum cascade laser materials.

Main Methods:

• Utilizing the Fabry-Perot (FP) reflectivity method with samples of varying heights.
• Employing a standard Fourier transform infrared spectrometer for spectral measurements.
• Conducting a thorough analysis of experimental errors and uncertainties.

Main Results:

• The FP method yields optical index measurements consistent with advanced ellipsometric techniques.
• Precise optical indices were determined for AlInAs, n-doped InGaAs, and InP in the 4–12 µm range.
• The study provides a comprehensive discussion of potential experimental errors and their impact.

Conclusions:

• The FP reflectivity method is a reliable and accessible technique for mid-infrared optical index measurements.
• This method offers enhanced precision when using samples with multiple heights.
• The obtained material data is valuable for the design and fabrication of quantum cascade lasers.