Electroluminescence of GeSn/Ge MQW LEDs on Si substrate

Area of Science:

• Materials Science
• Optoelectronics
• Semiconductor Physics

Background:

• Germanium-tin (GeSn) alloys are promising for optoelectronic applications due to their tunable bandgap.
• Quantum well structures are crucial for enhancing light-emitting properties in semiconductor devices.
• Integration of GeSn with silicon photonics is a key goal for on-chip optical communication.

Purpose of the Study:

• To grow and characterize multi-quantum well light-emitting diodes (LEDs) based on GeSn/Ge heterostructures on silicon.
• To investigate the optical properties and emission mechanisms of GeSn quantum wells at different temperatures.
• To analyze the influence of quantum confinement and strain on the electronic band structure of GeSn.

Main Methods:

• Epitaxial growth of ten alternating GeSn/Ge layers using molecular beam epitaxy (MBE) on a silicon substrate.
• Fabrication of multi-quantum well light-emitting diodes with specific Ge barrier and GeSn well dimensions and tin composition (7%).
• Electroluminescence (EL) spectroscopy measurements at room temperature (300 K) and low temperature (80 K).
• Spectral deconvolution of the electroluminescence to identify and analyze individual emission lines.
• Effective mass band structure calculations to support the interpretation of experimental results.

Main Results:

• Successful growth of GeSn/Ge multi-quantum well structures on silicon via MBE.
• Observation of broad and intensive luminescence bands in the electroluminescence spectra at both 300 K and 80 K.
• Deconvolution revealed three major emission lines originating from the GeSn quantum wells.
• These lines are attributed to quantum confinement effects, including two direct transitions (light hole and heavy hole) and one indirect transition.
• Evidence of biaxial compressive strain in the GeSn wells leading to light and heavy hole splitting.

Conclusions:

• The GeSn/Ge multi-quantum well structures exhibit promising electroluminescence properties for LED applications.
• Quantum confinement effects significantly influence the emission characteristics of the GeSn wells.
• The observed emission lines are consistent with theoretical predictions based on band structure calculations, confirming the role of strain and confinement.
• This work demonstrates the potential of MBE-grown GeSn/Ge heterostructures for silicon-based optoelectronics.