Piezoelectric polarization and quantum size effects on the vertical transport in AlGaN/GaN resonant tunneling diodes

In this work, the electronic properties of resonant tunneling diodes (RTDs) based on GaN-Al_xGa_(1-x)N double barriers are investigated by using the non-equilibrium Green functions formalism (NEG). These materials each present a wide conduction band discontinuity and a strong internal piezoelectric field, which greatly affect the electronic transport properties. The electronic density, the transmission coefficient, and the current-voltage characteristics are computed with considering the spontaneous and piezoelectric polarizations. The influence of the quantum size on the transmission coefficient is analyzed by varying GaN quantum well thickness, Al_xGa_(1-x)N width, and the aluminum concentration x_Al. The results show that the transmission coefficient more strongly depends on the thickness of the quantum well than the barrier; it exhibits a series of resonant peaks and valleys as the quantum well width increases. In addition, it is found that the negative differential resistance (NDR) in the current--voltage (I-V) characteristic strongly depends on aluminum concentration x_Al. It is shown that the peak-to-valley ratio (PVR) increases with x_Al value decreasing. These findings open the door for developing vertical transport nitrides-based ISB devices such as THz lasers and detectors.