Enhanced near-infrared absorption in lattice-matched Sc_0.14Al_0.86N/GaN multi-quantum wells: growth optimization and insights into polarization parameters

We report on the near-infrared intersubband (ISB) absorption properties of strain-free Sc 0.14 Al 0.86 N/GaN multiple quantum wells (MQWs) grown on c-plane GaN substrates by molecular beam epitaxy. These MQWs exhibit strong, sharp, and tunable absorption energies between 515 meV and 709 meV, for well widths ranging from 7 nm to 1.5 nm, respectively. Observation of ISB absorption in ultra-thin Sc 0.14 Al 0.86 N/GaN MQWs not only extends the near-infrared range accessible with Sc-containing nitrides but also highlights the challenges of growing nanometer-thick GaN quantum wells. We explore the effects of growth temperature on absorption characteristics and find that substrate temperatures above 600°C significantly enhance ISB absorption intensity but also introduce an energy redshift for the narrowest wells. The redshift is attributed to increased interface roughness due to ScAlN surface morphology degradation at higher temperatures. Additionally, a comparison of experimental results with simulated band-structures indicates that the magnitude of net polarization rises faster with Sc-composition than previously suggested by theoretical calculations. This study advances the prospects of ScAlN/GaN heterostructures for novel photonic devices in the technologically important near-infrared range.