Cyclotron resonance and magnetotransport measurements in AlxGa1−xN/GaN heterostructures for x=0.15–0.30

Cyclotron resonance (CR) and magnetotransport experiments have been performed on modulation Si-doped ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N/GaN}$ heterostructures with aluminum fraction $x$ varying from 0.15 to 0.30. A clear CR absorption and Shubnikov–de Haas oscillations have been observed. The CR line shapes are analyzed by calculating the high frequency conductivity of a two-dimensional electron gas. The obtained electron effective mass $m^{*}$ and scattering time τ are found to depend on the aluminum fraction $\mathrm{x.}$ For $\text{x=0.30}$ the measured CR frequency shifts significantly upward, which demonstrates the formation of potential fluctuations in ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N/GaN}$ heterostructures with large aluminum fraction $\mathrm{x.}$