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Electrically-pumped THz emitters based on plasma waves excitation in III-nitride structures

We report three approaches to development of electrically-pumped THz emitters based on III-Nitride structures. The first approach entails the investigation of two-dimensional (2D) plasmons in grating-gated AlGaN/GaN heterostructures performed at temperatures above liquid nitrogen by means of THz time-domain spectroscopy (TDS). Comparative analysis of the experimental data revealed the considerable phase shift of transmitted THz pulses at the resonant frequencies of collective oscillations of the grating-gated 2D electron gas (2DEG). The use of 2D plasmons is proposed for the development of tunable-frequency THz emitters with electrical control of the emission frequency, beam wave front and directivity. Another approach is based on the THz electroluminescence of shallow impurities such as oxygen and silicon in the standard AlGaN/GaN high electron mobility transistor (HEMT) structures. The surface plasmonphonon polaritons (SPPhP) in n-GaN grating are also considered for the development of electrically-pumped THz sources under thermal and electrical excitation of directive (coherent) radiation. We note that emission frequency can be governed either by gate voltage (2D plasmons) or structural design (SPPhP). All discussed methods are compared in terms of achieved quality factor, operating temperature and emitted power.