Spatial Mapping of Local Density Variations in Two-dimensional Electron Systems Using Scanning Photoluminescence

Area of Science:

• Semiconductor Physics
• Materials Science
• Quantum Engineering

Background:

• Two-dimensional electron systems (2DES) are fundamental to modern electronics.
• Precise characterization of electron density is vital for device performance.
• Existing methods have limitations in mapping local electron density variations.

Purpose of the Study:

• To develop and validate a scanning photoluminescence (PL) technique for direct, high-resolution mapping of local two-dimensional electron density.
• To investigate electron density homogeneity in high-quality Gallium Arsenide (GaAs) quantum well (QW) samples.
• To identify and quantify sources of local electron density fluctuations.

Main Methods:

• Development of a scanning photoluminescence (PL) technique.
• Direct mapping of local two-dimensional electron density with high relative accuracy (∼2.2 × 10^8 cm^-2).
• Analysis of electron density gradients and fluctuations in GaAs quantum well samples grown with and without substrate rotation.

Main Results:

• Successfully mapped local 2D electron density, confirming expected density gradients in non-rotated GaAs QW samples.
• Observed and quantified random local density fluctuations (∼1.2 × 10^9 cm^-2) in both rotated and non-rotated samples.
• Demonstrated that decreasing the buffer layer thickness significantly increases density fluctuations (to ∼9 × 10^9 cm^-2), indicating substrate-epitaxy interface effects.

Conclusions:

• The scanning PL technique provides direct, accurate measurement of local 2D electron density.
• Local density inhomogeneities exist even in high-quality 2D carrier systems.
• Residual space charges at the substrate-epitaxy interface are a significant source of these density fluctuations.