Investigation of the cap layer for improved GeSn multiple quantum well laser performance.

Area of Science:

• Optoelectronics
• Materials Science
• Semiconductor Physics

Background:

• Silicon-based light sources are crucial for integrated photonics.
• Silicon-Germanium-Tin (SiGeSn) heterostructures offer a pathway to achieving light emission in silicon.
• Optical confinement is a key factor influencing the performance of quantum well lasers.

Purpose of the Study:

• To investigate the effect of cap layer thickness on the performance of SiGeSn/GeSn multiple quantum well lasers.
• To determine the optimal cap layer design for enhanced optical confinement and lasing characteristics.
• To provide insights for the development of electrically injected SiGeSn quantum well lasers.

Main Methods:

• Growth of SiGeSn/GeSn multiple quantum well (4-well) devices with varying cap layer thicknesses (0, 190, 250, 290 nm) using chemical vapor deposition.
• Characterization of grown devices via optical pumping.
• Analysis of spontaneous emission and lasing properties at different temperatures.

Main Results:

• Devices with no cap or thin cap layers exhibited only spontaneous emission.
• Thicker cap layers (250 and 290 nm) enabled lasing up to 77 K.
• The 250 nm cap device showed lasing at 2440 nm with a threshold of 214 kW/cm².
• A clear trend between cap layer thickness and device performance was observed.

Conclusions:

• Cap layer engineering is critical for optimizing optical confinement in SiGeSn quantum well lasers.
• Thicker cap layers enhance optical mode overlap, leading to improved lasing performance.
• The findings provide valuable design guidelines for fabricating efficient, electrically injected SiGeSn-based lasers.