Polarization Effects in Graded AlGaN Nanolayers Revealed by Current-Sensing and Kelvin Probe Microscopy

Area of Science:

• Semiconductor physics
• Materials science
• Nanotechnology

Background:

• Aluminum gallium nitride (AlGaN) is a key material for electronic devices.
• Impurity doping in AlGaN can be challenging and introduce defects.
• Polarization doping offers an alternative doping mechanism.

Purpose of the Study:

• To experimentally investigate the relationship between Al concentration gradient and conductivity in AlGaN.
• To explore the effects of polarization engineering on electric fields and current transport.
• To assess the feasibility of achieving p-type conductivity via polarization doping.

Main Methods:

• Fabrication of graded AlGaN nanolayers with varying Al concentration gradients.
• Utilized cross-sectional Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (c-AFM).
• Correlated experimental electrical property measurements with simulations of electric fields and carrier densities.

Main Results:

• Electrical conductivity of graded AlGaN directly correlates with the magnitude of the Al concentration gradient.
• Experimental results for built-in electric fields and current transport align with theoretical simulations.
• Polarization-induced hole doping is limited by native n-type donors for gradients below 0.28%Al/nm.

Conclusions:

• Polarization doping in graded AlGaN effectively enhances conductivity without impurity dopants.
• Achieving reliable p-type conductivity in AlGaN remains difficult due to background impurities and native n-type donors.
• Further research is needed to overcome limitations for p-type doping in polarization-engineered AlGaN.