| With the advent of the 5G era,millimeter-wave/sub-millimeter waves have been widely used in wireless communications,and THz that has the higher frequency wave has the responsibility of future communication development.The THz radiation source is the focus of current research,and the Resonant Tunneling Diode(RTD)as a representative of the two-terminal negative resistance devices has a great application value and development.The RTD is based on the quantum-based resonant tunneling effect,which produces a negative differential resistance(NDR)that produces high-frequency oscillations in the AC circuit.Early researchers made Ga As-based RTD devices,but due to the limitations of GaAs materials,their output power was only a few microwatts and could not be used in high speed circuits.With the development of third-generation semiconductors in recent years,GaN has emerged as an outstanding representative of it.Due to its large energy gap,high mobility,and high thermal conductivity,GaN has become an important choice for making high-power RTD devices.In this paper,GaN-based RTD devices are used as research objects to fabricate complete devices,characterize and test them.Simulations are carried out according to deep microscopic mechanisms.The results are compared with experimental results to explain the causes of non-ideal effects,and improvement measures are proposed to verify its feasibility.These constitute the core of this article.This paper mainly includes two aspects: process preparation and theoretical analysis:In terms of process preparation,AlGaN/GaN and AlN/GaN heterojunctions were grown on a homogeneous GaN self-supporting substrate using Metal Organic Chemical Vapor Deposition(MOCVD)epitaxy.The epitaxial test pieces were characterized by resolution X-ray diffraction,Raman spectroscopy,transmission electron microscopy and field emission scanning electron microscopy.The epitaxial mass was judged according to the test results,and the working conditions and epitaxial thickness of MOCVD were continuously improved.Thereafter,a complete GaN-based RTD device was fabricated by using four different process flows,and the disadvantages and advantages of each process were analyzed according to the experimental results,and the most suitable process flow was selected.The ohmic contact electrode and the I-V DC characteristics of the device were tested.The results show that the RTD exhibits a clear NDR phenomenon on the forward voltage sweep,but there is a non-repeatable NDR effect,and the I-V characteristic exhibits an asymmetry when the device is subjected to forward and reverse bias voltage scanning.And after the scanning voltage increases from 0-5V,and then sweeps back from 5-0V,the NDR phenomenon disappears,hysteresis occurs.The non-reproducibility,hysteresis and asymmetry are analyzed from the microscopic mechanism.The parameters of the III-nitride material are calculated and the mobility,velocity field,ionization,embedded in the commercial Silvaco-Altas numerical simulation simulator are fitted.Based on the correlation coefficient parameters of the composite model,the III-nitride-related material model for simulation is obtained.On this basis,the GaN-based RTD device is successfully modeled by the planar unbalanced Green’s function electron transport model.The experimental results are analyzed by numerical model.The results reveal that it is the polarity that causes the strong built-in electric field to change the barrier structure,energy band and electron distribution of the effective region of the RTD,thus affecting the transmission coefficient and the ionization rate of the defect.The result is a decrease in the number of repeatable NDRs of the device and asymmetry and hysteresis of the forward and reverse bias currents.It is proposed to grow GaN materials along the non-polar direction to prepare non-polar RTD devices.The device structure and the ideal and higher performance GaN-based RTD devices are simulated.The feasibility of this method is verified from the theoretical simulation. |
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