Occupation of the double subbands by the two-dimensional electron gas in the triangular quantum well at ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ heterostructures

Magnetoresistance of modulation-doped ${\mathrm{Al}}_{0.22}{\mathrm{Ga}}_{0.78}\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ heterostructures has been studied by means of magnetotransport measurements at low temperatures and high magnetic fields. The double periodicity of the Shubnikov–de Haas oscillations was observed. It was found that the occupation of the first two subbands by the two-dimensional electron gas (2DEG) in the triangular quantum well at the ${\mathrm{Al}}_{0.22}{\mathrm{Ga}}_{0.78}\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ heterointerface took place when the 2DEG sheet concentration reached $7.2\times {10}^{12}{\mathrm{cm}}^{\mathrm{-}2}.$ The energy separation of the first and the second subbands in the quantum well was determined to be 75 meV just before the second subband was occupied. The quantum scattering time related to the first subband was determined to be $8.4\times {10}^{-14}\mathrm{s}.$