Effective mass of two-dimensional electron gas in an Al0.2Ga0.8N/GaN heterojunction

We have performed a magnetotransport study on an AlGaN/GaN heterostructure at low temperatures. The effective-mass values have been evaluated by analy zing the exact form of the temperature-dependent Shubnikov-de Haas oscillat ion function. The values obtained increase with the magnetic field. This ma ss enhancement is attributed to conduction-band nonparabolicity. The effect ive-mass variation with the magnetic field was extrapolated to zero field, together with further correction due to the triangular confinement of the c arriers, yielding an effective mass of 0.185 +/-0.005 of the free-electron mass. Our result is in excellent agreement with the results obtained by fir st-principle calculations and the tight-binding method, and suggest the sig nificance of magnetic-field-induced nonparabolicity in transport measuremen ts. (C) 2001 American Institute of Physics.