Unintentional doping in GaN.

Area of Science:

• Materials Science
• Semiconductor Physics
• Device Engineering

Background:

• Optimizing gallium nitride (GaN) based devices necessitates precise control over material doping.
• Unintentional doping, especially in lateral transport electronic devices, degrades performance.
• For heteroepitaxial GaN grown in the polar (0001) orientation, unintentional doping is primarily concentrated near the GaN/substrate interface.

Purpose of the Study:

• To investigate the origins and distribution of unintentional doping in various GaN epitaxial orientations.
• To understand the role of growth facets and substrate interactions in impurity incorporation.
• To identify strategies for mitigating unintentional doping in GaN device fabrication.

Main Methods:

• Utilizing scanning capacitance microscopy (SCM) to map carrier concentration.
• Analyzing impurity incorporation across different GaN growth orientations (polar, semi-polar, non-polar).
• Examining the impact of three-dimensional growth phases (e.g., epitaxial lateral overgrowth) on doping profiles.

Main Results:

• High incorporation of gas-phase impurities, mainly oxygen, during early growth stages contributes to unintentional doping, particularly on N-rich semi-polar facets.
• Three-dimensional growth strategies can alter facet composition, influencing dopant incorporation.
• Semi-polar GaN layers show significant doping throughout, while non-polar layers are affected by oxygen diffusion from sapphire substrates along stacking faults.

Conclusions:

• Understanding facet-dependent impurity incorporation is key to controlling unintentional doping in GaN.
• Growth orientation and strategies like epitaxial lateral overgrowth significantly influence doping profiles.
• Minimizing oxygen incorporation and managing substrate diffusion are critical for high-performance GaN devices.