Effect of temperature on 2D terahertz plasmons in AlGaN/GaN heterostructures

The effect of temperature on delocalized and localized plasmonic modes in large-area AlGaN/GaN plasmonic crystals formed by grating-gates and by ungated arrays of disks with two-dimensional electron gas was studied experimentally. The temperature dependences of the plasmon frequency was characterized by hysteresis and high dispersion of the experimental data across different plasmonic crystals, which was attributed to the uncertainty of the surface states on the open surface of AlGaN and the corresponding uncertainty of the electron concentration in the ungated parts. The redshift of the plasmon frequency with temperature increase was explained by the combined effect of temperature dependence of the electron concentration in the ungated parts and the electron effective mass. The temperature dependence of the electron effective mass in GaN was analyzed based on the results of the cyclotron resonance measurements using the simplified approach and taking losses into account. It was demonstrated that indeed, the electron effective mass increases (1.5-2) times at temperatures from T = 70 K to T = 290 K. The strong temperature dependence of such a basic parameter should be taken into account when designing GaN-based electronic, optoelectronic, and terahertz plasmonic devices.