Surface treatments affect GaN surface quantum well emission

Surface quantum wells (SuQWs), comprised of a thin layer of lower bandgap semiconductor sandwiched between a vacuum or air interface and a higher bandgap semiconductor, are sensitive to surface adsorbents that enhance or diminish surface recombination velocities. For non-centrosymmetric semiconductors, such as III-Nitrides used in high-electron-mobility transistors and sensors, the surface charge can enhance or diminish the intrinsic spontaneous polarization in the SuQW. Using photoluminescence spectroscopy of GaN SuQWs, we report increases in optical emission efficiency, shifts in polarization, and changes in confinement energies as large as ±15 meV following successive exposure of the surface to an acid or a base. To explain these effects, we propose a model in which the relative electronegativity of adsorbates to that of the nitrogen on gallium-terminated surfaces enhances or diminishes the SuQW polarization. We use this polarization model to elucidate the mechanisms responsible for the observed increase in emission efficiency.