Photoluminescence from GeSn nano-heterostructures.

Area of Science:

• Materials Science
• Nanotechnology
• Semiconductor Physics

Background:

• Germanium-tin (GeSn) alloys are promising for optoelectronic applications.
• Controlling Sn distribution in GeSn nanostructures is crucial for device performance.
• Heteroepitaxial growth of GeSn on silicon (Si) presents challenges due to lattice mismatch and thermal stability.

Purpose of the Study:

• To investigate the spatial distribution of tin (Sn) within GeSn nano-heteroepitaxial clusters.
• To understand the role of a germanium (Ge) capping layer on Sn incorporation and surface segregation.
• To correlate the observed Sn distribution with photoluminescence properties.

Main Methods:

• Molecular beam epitaxy (MBE) at 600 °C on Si-patterned substrates for selective GeSn nano-cluster growth.
• Deposition of a thin Ge cap layer to induce Sn incorporation from surface droplets.
• Characterization of Sn distribution and photoluminescence emission.

Main Results:

• GeSn nano-clusters with 1.4 ± 0.5 at% Sn were selectively grown.
• Sn droplets were observed on the faceted surfaces of the nano-clusters.
• A Ge cap layer induced Sn incorporation into a wetting layer (8 ± 0.5 at% Sn) on the nano-dot surfaces.
• Strong photoluminescence emission was observed, attributed to direct recombination in the Sn-rich outer region of the GeSn nano-dots.

Conclusions:

• Selective growth of GeSn nano-clusters is achievable at high temperatures.
• A Ge capping strategy effectively incorporates segregated Sn into a wetting layer, increasing Sn concentration.
• The Sn-rich wetting layer significantly contributes to the observed photoluminescence, indicating potential for optoelectronic device applications.