Near-infrared intersubband absorption in epitaxially grown Sc_xAl_1-xN/GaN multi quantum wells

The seamless integration of ultrawide-bandgap ScAlN with the GaN technology, along with its high piezoelectric response and ferroelectric properties, makes it a promising material for the fabrication of novel high-power, high electron mobility transistors, memory storage devices, and quantum photonic devices. In this work, the optical and electronic properties of lattice-matched Sc_0.18Al_0.82N/GaN superlattices (multi quantum wells/barriers) grown on polar c-plane GaN substrates by plasma-assisted molecular beam epitaxy were investigated. Direct Fourier transform infrared spectroscopy was used to measure near-infrared intersubband (ISB) absorption in the samples. The ISB transition energies are widely tunable by engineering the conduction band profile (i.e. layer compositions and thicknesses) and are constrained only by conduction band offsets. All samples exhibited strong and narrow absorption peaks in the near infrared range of 640 meV to 520 meV. Band structure calculations confirmed these results and showed excellent confinement of electrons in the quantum wells. The ISB energies given by 8-band k.p calculations were corrected by including many-body effects and the charge concentration was measured by Hall measurements.