Improved Negative Differential Mobility Model of GaN and AlGaN for a Terahertz Gunn Diode

This paper presents an improved negative differential mobility model for GaN and AlGaN to simulate GaN Gunn diodes at terahertz frequencies. Temperature-dependent parameters vsat, Ec, α, δ, and γ are proposed to improve the accuracy of the mobility model at high temperatures. In particular, an Al-composition-related coefficient fZ(x) and a random-alloy-potential-related factor falloy(p) are developed for an AlGaN mobility model. Simulation results show that notched doping GaN and AlGaN/GaN heterostructure Gunn diodes, both including 0.6-m transit and 0.2-m electron launching regions, have the capability of generating fundamental frequencies of 352-508 and 332-469 GHz, respectively, with a maximum radio-frequency (RF) power density of ~1010 W/cm3 and RF efficiency of over 2% accompanied with a shift of an oscillation mode from a dipole-domain mode toward an accumulation mode as the temperature rises from 300 to 500 K.