Momentum space imaging reveals chemical gating of 2D electron and hole gases in nitride heterostructures

Gallium nitride (GaN) and aluminum nitride (AlN) host high-density two-dimensional electron and hole gases in undoped GaN quantum wells, created by built-in polarization fields and favorable band offsets. These interfacial states are essential for many high-power and high-frequency devices, yet momentum-resolved measurements (particularly under applied bias) remain rare due to two challenges: (i) the surface sensitivity of conventional vacuum-ultraviolet ARPES, which cannot probe deeply buried states, and (ii) the difficulty of implementing electrostatic gating in semiconductor heterostructures due to leakage currents. Here, we use soft X-ray ARPES to overcome the first challenge, directly accessing quantized states several nanometers below the surface in GaN/AlN heterostructures and relating their subband dispersions to transport characteristics. As a precursor to gated ARPES, we employ controlled oxygen adsorption to chemically tune the potential and track the resulting band shifts. This approach opens a pathway toward fully gate-tunable, momentum-resolved studies of buried states in wide-bandgap devices. Gallium nitride and aluminum nitride quantum wells are crucial for high-power devices, yet probing their buried electronic states remains challenging. Here, the authors utilize soft X-ray ARPES and controlled oxygen adsorption to access and tune these states, paving the way for advanced momentum-resolved studies in wide-bandgap semiconductors.