Two-dimensional electron-gas AlN/GaN heterostructures with extremely thin AlN barriers

Plasma-assisted molecular-beam epitaxy is used to grow a set of two-dimensional electron-gas AlN/GaN structures with AlN barrier thicknesses varied between 24 and 50 Å. The density of the two-dimensional electron gas formed at the GaN/AlN interface increases from ${\text{1.51×10}}^{13} {\mathrm{cm}}^{\mathrm{-2}}$ for the AlN barrier width of 24 Å to ${\text{3.65×10}}^{13} {\mathrm{cm}}^{\mathrm{-2}}$ for the AlN barrier width of 49 Å. The increase in the electron sheet density is accompanied by a decrease in electron mobility related to tensile strain relaxation and enhanced interface roughness scattering. It is shown that room-temperature sheet resistances below 200 Ω/□ can be achieved in AlN/GaN high electron mobility transistor structures with 35–45 Å AlN barriers.