Elimination of remnant phases in low-temperature growth of wurtzite ScAlN by molecular-beam epitaxy

Growth of wurtzite Sc_xAl_1−xN (x < 0.23) by plasma-assisted molecular-beam epitaxy on c-plane GaN at high temperatures significantly alters the extracted lattice constants of the material due to defects likely associated with remnant phases. In contrast, ScAlN grown below a composition-dependent threshold temperature exhibits uniform alloy distribution, reduced defect density, and atomic-step surface morphology. The c-plane lattice constant of this low-temperature ScAlN varies with composition as expected from previous theoretical calculations and can be used to reliably estimate alloy composition. Moreover, lattice-matched Sc_0.18Al_0.82N/GaN multi-quantum wells grown under these conditions display strong and narrow near-infrared intersubband absorption lines that confirm advantageous optical and electronic properties.