Probing semiconductor gap states with resonant tunneling.

Area of Science:

• Solid State Physics
• Materials Science
• Surface Science

Background:

• Gallium Arsenide (GaAs) {110} surfaces exhibit complex electronic properties.
• Understanding tunneling transport is crucial for semiconductor device applications.
• Shallow acceptors play a significant role in the electronic behavior of semiconductors.

Purpose of the Study:

• To investigate tunneling transport through the depletion layer of a GaAs {110} surface.
• To elucidate the origin of negative differential conductivity observed in such systems.
• To analyze the role of shallow acceptors in mediating tunneling transport and creating anisotropic patterns.

Main Methods:

• Utilizing low temperature scanning tunneling microscopy (STM) for high-resolution surface analysis.
• Performing tunneling spectroscopy to probe electronic states within the GaAs band gap.
• Analyzing energetically and spatially resolved spectra to understand transport mechanisms.

Main Results:

• Observed negative differential conductivity attributed to resonant enhancement of tunneling probability.
• Identified individual shallow acceptors as mediators of this resonant tunneling.
• Demonstrated that evanescent states in the GaAs band gap are probed at specific bias voltages.
• Revealed pronounced anisotropic contrast patterns of shallow acceptors linked to a specific transport channel.

Conclusions:

• The observed anisotropic contrast patterns are exclusively associated with the resonant tunneling channel mediated by shallow acceptors.
• The complex band structure of GaAs, related to its zinc blende symmetry, is responsible for the observed anisotropies.
• Findings provide insights into surface electronic transport phenomena in semiconductors.