Characterization of an AlGaN/GaN two-dimensional electron gas structure

An ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N/GaN}$ two-dimensional electron gas structure with $\text{x=0.13}$ deposited by molecular beam epitaxy on a GaN layer grown by organometallic vapor phase epitaxy on a sapphire substrate was characterized. X-ray diffraction maps of asymmetric reciprocal lattice points confirmed that the thin AlGaN layer was coherently strained to the thick GaN layer. Methods for computing the aluminum mole fraction in the AlGaN layer by x-ray diffraction are discussed. Hall effect measurements gave a sheet electron concentration of ${\text{5.1×10}}^{12} {\mathrm{cm}}^{\text{−2}}$ and a mobility of ${\text{1.9×10}}^4 {\mathrm{cm}}^{\mathrm{2}}\mathrm{/V s}$ at 10 K. Mobility spectrum analysis showed single-carrier transport and negligible parallel conduction at low temperatures. The sheet carrier concentrations determined from Shubnikov–de Haas magnetoresistance oscillations were in good agreement with the Hall data. The electron effective mass was determined to be ${\text{0.215±0.006\hspace{0.05em}m}}_0$ based on the temperature dependence of the amplitude of Shubnikov–de Haas oscillations. The quantum lifetime was about one-fifth of the transport lifetime of ${\text{2.3×10}}^{\text{−12}} \mathrm{s}.$