Tuning quantum dot luminescence below the bulk band gap using tensile strain

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Self-assembled quantum dots (SAQDs) under biaxial tension offer reduced band gaps for optoelectronics.
• Tensile strain in Germanium (Ge) can induce a transition from indirect- to direct-gap.
• Dislocations have previously hindered the growth of tensile SAQDs.

Purpose of the Study:

• To demonstrate a method for growing dislocation-free tensile SAQDs.
• To enable novel devices utilizing tensile SAQDs for mid-infrared optoelectronics.
• To overcome limitations in current tensile SAQD fabrication.

Main Methods:

• Utilizing (110)-oriented surfaces for unique strain relief mechanisms.
• Growing tensile Gallium Arsenide (GaAs) SAQDs on Indium Aluminum Arsenide (InAlAs) (110) surfaces.
• Characterizing the SAQDs for strain, confinement, and optical properties.

Main Results:

• Successfully grew spontaneous, controllable, and dislocation-free tensile GaAs SAQDs.
• Achieved a ~40% band gap reduction in GaAs SAQDs due to tensile strain.
• Observed robust type-I quantum confinement and photoluminescence at lower energies than bulk GaAs.

Conclusions:

• The developed method allows for dislocation-free tensile SAQDs.
• This technique can be applied to various zinc blende and diamond cubic materials.
• Enables the creation of new optoelectronic devices based on tensile SAQDs.