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

An AlxGa1-xN/GaN two-dimensional electron gas structure with x=0.13 deposit ed by molecular beam epitaxy on a GaN layer grown by organometallic vapor p hase epitaxy on a sapphire substrate was characterized. X-ray diffraction m aps of asymmetric reciprocal lattice points confirmed that the thin AlGaN l ayer was coherently strained to the thick GaN layer. Methods for computing the aluminum mole fraction in the AlGaN layer by x-ray diffraction are disc ussed. Hall effect measurements gave a sheet electron concentration of 5.1x 10(12) cm(-2) and a mobility of 1.9x10(4) cm(2)/V s at 10 K. Mobility spect rum analysis showed single-carrier transport and negligible parallel conduc tion at low temperatures. The sheet carrier concentrations determined from Shubnikov-de Haas magnetoresistance oscillations were in good agreement wit h the Hall data. The electron effective mass was determined to be 0.215 +/- 0.006 m(0) based on the temperature dependence of the amplitude of Shubnik ov-de Haas oscillations. The quantum lifetime was about one-fifth of the tr ansport lifetime of 2.3x10(-12) s. (C) 2000 American Institute of Physics. [S0021-8979(00)08001-4].