Composition-controlled recovery time of SWIR (2-2.4 µm) GaSb-based SESAMs.

Area of Science:

• Optics and Photonics
• Materials Science
• Ultrafast Lasers

Background:

• Semiconductor Saturable Absorber Mirrors (SESAMs) are crucial for ultrafast lasers, with established near-infrared (NIR) applications using GaAs.
• There is growing demand for SESAMs in the short-wave infrared (SWIR) spectrum, necessitating the use of the GaSb material system.
• GaSb-based SESAMs offer inherent ultrafast response and unique interactions between response time and fabrication, distinct from GaAs counterparts.

Purpose of the Study:

• To investigate the advanced interplay between fabrication parameters and nonlinear response in GaSb-based SESAMs for SWIR applications.
• To analyze the impact of lattice mismatch (strain) in quantum wells (QWs) and barrier materials on SESAM performance.
• To optimize SESAM design for center wavelengths between 2 and 2.4 µm.

Main Methods:

• Growth of SESAMs using GaSb material system with varying quantum well compositions (InGaSb, GaAsSb, In(x)Ga(1-x)As(y)Sb(1-y)) and lattice mismatch levels.
• Fabrication of SESAMs with In0.27GaSb QWs and AlxGa1-xAsSb barriers with varying aluminum content.
• Characterization of interband recovery times for different strain levels and barrier compositions.

Main Results:

• A strong dependence of recovery time on QW strain was observed; lattice-matched QWs (-0.1% LMM) showed a maximum recovery time of 340 ps.
• Both compressive (-1.7% LMM) and tensile (+0.9% LMM) strained QWs exhibited shorter interband recovery times compared to lattice-matched ones.
• Increased aluminum content in AlxGa1-xAsSb barriers significantly slowed down the interband recovery time.

Conclusions:

• Quantum well strain in GaSb-based SESAMs critically influences ultrafast response, with strained QWs leading to faster recovery times.
• Barrier material composition, specifically aluminum content, plays a significant role in modulating the recovery dynamics.
• These findings provide advanced insights for designing high-performance SESAMs for SWIR ultrafast laser applications.