Antiphase disorder in GaAs/Ge heterostructures for solar cells

Area of Science:

• Materials Science
• Semiconductor Physics
• Epitaxial Growth

Background:

• Antiphase disorder is a critical issue in metal organic vapour phase epitaxy (MOVPE) grown III-V/ (100)Ge heterostructures.
• This disorder impacts the performance of devices like GaAs solar cells.

Purpose of the Study:

• To investigate antiphase disorder in GaAs/(100)Ge heterostructures.
• To understand the mechanisms of antiphase domain formation and annihilation.
• To identify conditions for achieving antiphase domain-free epitaxy and its impact on solar cell efficiency.

Main Methods:

• Chemical etching
• Transmission electron microscopy (TEM)
• Cathodoluminescence (CL) analysis

Main Results:

• Antiphase domains self-annihilate at the surface, reducing domain size with increasing substrate misorientation.
• Antiphase domain-free epitaxy achieved for substrate miscuts > 3 degrees towards [111].
• Reversal in sublattice location observed with varying misorientation angle and growth temperature, explained by a surface step nucleation model.
• Strong interaction between antiphase boundaries and misfit dislocations noted.
• High densities of antiphase domains found in initial GaAs layers of solar cells, but successfully overgrown by single-phase material.

Conclusions:

• Substrate misorientation and growth temperature are key parameters to control antiphase disorder.
• Optimized epitaxy conditions enable high-quality GaAs/(100)Ge heterostructures.
• Overgrowth of initial antiphase domains is crucial for realizing high-efficiency GaAs solar cells on Ge.