Enhancement of 2DEG effective mass in AlN/Al0.78Ga0.22N high electron mobility transistor structure determined by THz optical Hall effect

We report on the free charge carrier properties of a two-dimensional electron gas (2DEG) in an AlN/AlxGa1-xN high electron mobility transistor structure with a high aluminum content (x = 0.78). The 2DEG sheet density N s = ( 7.3 +/- 0.7 ) x 10 12 cm(-2), sheet mobility mu s = ( 270 +/- 40 ) cm(2)/(Vs), sheet resistance R- s = ( 3200 +/- 500 ) omega/ ?, and effective mass m( eff) = ( 0.63 +/- 0.04 ) m( 0) at low temperatures ( T = 5 K ) are determined by terahertz (THz) optical Hall effect measurements. The experimental 2DEG mobility in the channel is found within the expected range, and the sheet carrier density is in good agreement with self-consistent Poisson-Schrodinger calculations. However, a significant increase in the effective mass of 2DEG electrons at low temperatures is found in comparison with the respective value in bulk Al0.78Ga22N ( m( eff) = 0.334 m( 0)). Possible mechanisms for the enhanced 2DEG effective mass parameter are discussed and quantified using self-consistent Poisson-Schrodinger calculations .Published under an exclusive license by AIP Publishing.
Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program [2016-05190]; Chalmers University of technology; Ericsson; United Monolithic Semiconductors (UMS); Volvo Cars; Swedish Research Council Vetenskapsradet (VR) [2016-00889]; Swedish Foundation for Strategic Research [RIF14-055, EM16-0024]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoeping University, Faculty Grant Stark forskningsmiljoe (SFO) Mat LiU [2009-00971]; National Science Foundation [DMR 1808715, OIA-2044049]; Air Force Office of Scientific Research [FA9550-18-1-0360, FA9550-19-S-0003, FA9550-21-1-0259]