| At present,we have entered the 5G era,and the research and development of the next-generation mobile communication technology,namely 6G,has also begun.In the 6G era,electromagnetic waves will enter the terahertz frequency band.Terahertz waves usually refer to electromagnetic waves with a frequency of 0.1 to 1 THz,and the corresponding wavelength range is 30 to 3000 μm.This frequency band has been called the "terahertz gap" for a long time,but its special position in the electromagnetic spectrum makes it not only been used in communications,but also has great application potential in aerospace,biology,chemistry,medical,security and other fields.At present,common terahertz radiation sources are mainly generated based on optical and vacuum electronics technologies,such as quantum cascade lasers,etc.In terms of semiconductor solid-state radiation sources,Gunn diodes,resonant tunneling diodes and avalanche time diodes have more potential,and more related research has been carried out.Electron transfer between energy valleys can also occur in High Electron Mobility Transistor(HEMT)devices based on GaN materials,and Gunn oscillation occurs in the conductive channel,thereby generating a signal output in the terahertz band.As the third-generation wide-bandgap semiconductor material,GaN material has a larger forbidden band width and higher electron mobility compared with the widely used Si materials and Ga As materials.AlGaN/GaN is formed to heterojunction witch has a strong spontaneous polarization effect and piezoelectric polarization effect,so that a higher concentration of two-dimensional electron gas can be obtained.In addition,the thickness of each epitaxial layer of HEMT devices can be precisely controlled by MBE and other material growth techniques,and the distance of gate-source and gate-drain can also be controlled by photolithography,which has excellent compatibility with devices and circuits under conventional planar technology.It is easy to realize terahertz monolithic integrated circuit.Therefore,in high frequency and high power applications,GaN-based high electron mobility transistors have greater application prospects.Based on this,this paper aims to conduct an exploratory study on current oscillations in the terahertz band in GaN-based AlGaN/GaN HEMT devices,expecting to obtain useful output of higher harmonic components.The research content mainly includes Atlas modeling of HEMT devices with notch structure and field plate structure,and analysis of Gunn oscillation effect in the device.And the process realization of AlGaN/GaN single heterojunction HEMT devices containing notch structure and field plate structure is also obtained.The research work in this paper is supported by the National Natural Science Foundation of China’s general project "Research on GaN-based harmonic-enhanced high electron mobility transistors for terahertz applications".The main contents include the following aspects:First introduced the basic knowledge of terahertz wave,including the definition of terahertz wave and its application in communications,etc.,introduced the research history of terahertz technology,introduced the research status of terahertz technology.We also introduced the GaN materials which is the representative of the third-generation wide-bandgap semiconductor materials.Highlighting its huge application potential in high-frequency and high-power scenarios.Secondly,the Gunn oscillation effect in the AlGaN/GaN single heterojunction HEMT device is theoretically studied.Based on the drift diffusion and energy balance transport model of the Silvaco-Atlas simulation simulator,we use the velocity field relationship model built by the research team including energy relaxation time,electron temperature and lattice temperature.This provides a good description of the negative resistance characteristics of GaN materials.In the HEMT device with notch structure,the influence of the gate electrode length on the Gunn oscillation frequency in the device conduction channel is studied.As the length of the gate electrode decreases,the current oscillation frequency will gradually increase;the notch structure is studied the influence of the length and depth on the Gunn oscillation frequency in the conductive channel of the device.As the notch length decreases and the depth become shallower,the current oscillation frequency will gradually increase.At the same time,the effect of the number of groove structures is studied,the fundamental frequency component in the double groove HEMT device is reduced,but the higher harmonic component is increased,realizing the effect of harmonic enhancement.In HEMT devices with a gate field plate structure,the influence of the length of the gate field plate on the Gunn oscillation frequency in the device channel is studied.As the length of the gate field plate decreases,the current oscillation frequency will gradually increase.This part of the theoretical research work on the Gunn oscillation effect in HEMT devices also plays a theoretical support role for the subsequent tape-out research.With the help of the conventional AlGaN/GaN HEMT device process preparation line,the HEMT device containing the notch structure was realized in the process to explore the Gunn Oscillation in the real devices,and related tests were completed to verify the modulation effect of the notch structure on the HEMT channel electric field.And the improvements of the breakdown characteristics,current collapse effect and cut-off frequency characteristics of the devices are also obtained.An AlGaN/GaN HEMT device with a field plate structure was also realized in the process to explore the Gunn Oscillation in the real device,and several different discontinuous gate field plate structures were designed,which also verified the modulation effect of the field plate structure on the channel electric field of the HEMT device.Comparative studies of the effects of different gate field plate lengths and gate field plate density on the device characteristics are discussed,and the discontinuous gate field plate structure improves the cut-off frequency characteristics of the device.This paper innovatively proposes a sandwich structure consisting of a notch structure,Si N and a field plate structure,and based on the simulation research,an AlGaN/GaN HEMT device with a sandwich structure is realized in the process to explore the Gunn Oscillation in the real device.The dual suppression effect of the peak electric field in the HEMT device channel is verified.The sandwich structure improves the breakdown characteristics,current collapse effect and cut-off frequency characteristics of the device,and finally improves the JFOM quality factor of the device.The relevant theoretical and experimental research work on harmonic enhancement of GaN-based HEMT devices in this paper is summarized,and the problems and research directions that may need to be solved in the future for GaN-based HEMT devices to achieve terahertz signal output are pointed out. |
