Al0.15Ga0.85N/GaNheterostructures: Effective mass and scattering times

We have observed well-resolved Shubnikov–de Haas oscillations in the two-dimensional electron gas in ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ heterojunctions, and determined the GaN electron effective mass ${(m}^{*})$ and the quantum scattering time $\left({\tau }_q\right)$. We found $m^{*}{=0.18m}_0\pm {0.02m}_0$ in agreement with theoretical calculations, but slightly smaller than the values previously reported from optical experiments. The value of ${\tau }_q$ was found to be $0.13\times {10}^{-12}$ sec, which is about a factor of 6 smaller than the classical scattering time $({\tau }_c=0.77\mathrm{}\times {10}^{-12}$ sec). This difference between ${\tau }_q$ and ${\tau }_c$ is attributed to a significant amount of small angle scattering, most likely due to charged defects at the epilayer/substrate interface.