Enhancement of Negative Differential Mobility Effect in Recessed Barrier Layer AlGaN/GaN HEMT for Terahertz Applications

A recessed barrier layer (RBL) structure is proposed in the micrometer-sized AlGaN/GaN high-electron mobility transistor (HEMT) for terahertz applications. It is found by using numerical simulation that the properly designed RBL structure can trigger the formation and propagation of electron domains in the 2-D electron gas (2-DEG) channel. As a result, the fundamental frequency can be extended even up to terahertz regime, and also it can be tuned in a certain range by the bias voltage of Schottky contact gate that acts as a hot-electron injector just like the notch-doped Gunn diode. Our simulations show that the 0.3-μm-gate HEMT with the RBL structure having the depth of 10-15 nm and the length of 200-400 nm can generate the stable and tunable oscillations in the range of around 0.8-1.6 THz under the normally gate bias of -0.2-0.4 V, as well as the ratio of RF-to-dc current component ranging from 3.04% to 7.2%. These available characteristics come from the redistribution of electric field in the 2-DEG channel. Compared with the ungated and the top-gated planar Gunn diodes ever reported, the proposed RBL structural AlGaN/GaN HEMT can be easily fabricated and operated under normal conditions, demonstrating a great potential application in terahertz radiation sources.