Study On GaN Based Terahertz HEMTs With Buried Layer

Terahertz(THz)waves have shown great application potential in the fields of medical imaging,astronomical detection,security inspection,and communications.The research on terahertz source technology has always been one of the international hot research topics.As the third-generation wide-gap semiconductor material,gallium nitride(Ga N)has a higher Johnson quality factor,electron effective mass,longitudinal optical phonon energy,and heterojunction two-dimensional electron gas(2DEG)density.These characteristics make it have excellent power and frequency performance,which is very suitable for applications in the terahertz frequency band.Gallium nitride-based high electron mobility transistor(HEMT)is the core device of terahertz circuit,which plays a decisive role in circuit performance.However,there are few studies on the Gunn oscillation phenomenon in Ga N-based HEMT devices.The extremely high electron concentration of 2DEG at the Al Ga N/Ga N heterojunction interface and the low scattering of ionized impurities are very conducive to the formation of electronic domains.The peak of the electric field at the edge of the gate provides electric field perturbation,which can be used to trigger Gunn oscillation.The Gunn oscillation in Ga N-based HEMT has been proved by related experiments and theoretical studies,and its oscillation frequency can reach the terahertz range.By further adjusting the device structure,Ga N-based HEMT has the potential as a semiconductor broadband THz radiation source.In this paper,a p-Ga N island buried layer(PIBL)structure is introduced in the buffer layer below the edge of the gate near the drain in the traditional Ga N-based HEMT device structure.The introduction of the PIBL structure can adjust the electric field distribution in the 2DEG channel at the edge of the gate of the device,thereby further enhancing the Gunn effect in the device and promoting the formation of electronic domains.Based on the Silvaco ATLAS simulation software,this paper models the PIBL structure HEMT device,and uses the energy balance model(EB model)to simulate the oscillation characteristics of the device.The PIBL structure's modulation effect on the electric field and electron concentration distribution in the device channel is mainly studied,and the working mechanism of the PIBL structure to promote the formation of electronic domains is explained.This paper also focuses on the influence of simulation parameters such as p-Ga N doping concentration N_p,gate-source voltage V_gs,and the position p-Ga N island buried layer on the oscillation characteristics of the device and its internal mechanism.The change of the oscillation frequency is mainly caused by the change of the 2DEG electron concentration and electric field distribution in the PIBL region of the 2DEG channel under different simulation parameters.By reasonably designing the relevant parameters of the device,the current oscillation frequency can reach the terahertz range.In addition,this paper also deeply studied the multi-domain coexistence phenomenon in PIBL structure HEMT devices.The number and size of the electronic domains in the device are obviously affected by the applied bias voltage,and the working mode of the device can be adjusted by adjusting the drain-source voltage(V_ds).The high concentration of 2DEG allows the formation of narrower domains and provides conditions for the generation of multiple electronic domains in the channel of the device.The superposition of multiple electronic domains will cause the fundamental frequency of the oscillating current to decrease while the high-order harmonic components increase,making the non-linear characteristics of the oscillating current significantly enhanced.The oscillation frequency of the device can be further improved by making the device work at the harmonic frequency.