Quantum of optical absorption in two-dimensional semiconductors

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Understanding optical absorption in low-dimensional materials is crucial for advanced electronic and photonic applications.
• Two-dimensional (2D) semiconductor nanomembranes offer unique quantum confinement effects influencing their optical properties.
• Previous theoretical work predicted quantized absorption in 2D systems, but experimental verification in various materials is ongoing.

Purpose of the Study:

• To experimentally investigate the optical absorption characteristics of free-standing indium arsenide (InAs) nanomembranes.
• To determine the thickness dependence of optical absorption in InAs nanomembranes.
• To validate the theoretical concept of absorptance quantization in a specific 2D semiconductor system.

Main Methods:

• Fabrication of free-standing InAs nanomembranes with thicknesses ranging from 3 nm to 19 nm.
• Characterization of optical absorption using Fourier transform infrared (FTIR) spectroscopy at room temperature.
• Analysis of experimental data in comparison with theoretical predictions for 2D semiconductor absorptance.

Main Results:

• Stepwise optical absorption was observed in InAs nanomembranes, attributed to interband transitions between 2D subbands.
• The absorptance per step was consistently measured at approximately 1.6%, irrespective of the nanomembrane thickness.
• Experimental findings align with the theoretical prediction of a quantized absorptance (AQ = πα/nc) for 2D interband transitions.

Conclusions:

• Absorptance quantization is experimentally confirmed in InAs nanomembranes, supporting its universality in 2D systems.
• The observed phenomenon is independent of material thickness, highlighting a fundamental quantum mechanical effect.
• This finding has implications for the design and application of novel 2D materials in optoelectronics.