Research On Characteristics And Process Of GaN-based Terahertz IMPATT Diode

Due to the excellent electromagnetic wave characteristics,including spectral resolution,penetrating imaging and broadband,terahertz frequency band has shown broad application prospects in military security communications and civilian imaging detection,it has become a hot research object in global frontier scientific research in recent years.At present,among terahertz radiation sources,IMPATT diode has gradually become a research hotspot due to its high power output,and is widely used in military and civilian fields,such as communications,radar and other systems.Devices based on Si and GaAs materials have gradually shown their disadvantages in the application process due to the material’s physical conditions,and cannot be used in high temperature,high frequency,large power,anti-radation,optoelectronic devices and other fields,while the third-generation semiconductor GaN materials have many advantages.IMPATT diode based on GaN material will show excellent high-frequency and high-power performances,it is expected to have much higher power output capability than Si,Ga As-based IMPATT diode.This paper studies the process and characteristics of GaN-based IMPATT diode,and provides new ideas for the application of IMPATT diode in terahertz regime.The main contents of this paper are:1.The n-type doped low-high-low epitaxial structure of GaN-based IMPATT diodes was designed,the IMPATT device epitaxial materials were grown on the flat and patterned sapphire substrates by MOCVD epitaxial growth technology,the quality of the epitaxial wafers was analyzed by material characterization technology.The layout and manufacturing steps of GaN-based IMPATT diode are designed,GaN-based IMPATT diodes on flat and patterned sapphire substrates are experimentally obtained.The avalanche breakdown characteristics of GaN-based IMPATT diodes on the patterned sapphire substrate were verified by testing the ohmic contact,Schottky contact and reverse breakdown properties of the IMPATT diodes.According to the epitaxial layer test and the experimental results of the IMPATT diodes,the structure and physical models of the GaN-based IMPATT diode are established on the Silvaco-ATLAS numerical simulation platform.2.Based on the established structure and physical models of GaN-based IMPATT diodes in Silvaco-ATLAS,the noise characteristics the single drift-region Schottky barrier IMPATT diodes based on the polar and nonpolar orientation wurtzite GaN materials were studied.When the DC bias current densities of the IMPATT diode are 1,10 and 100 k A/cm~2,respectively,comparing with the polar IMPATT diode,the upper limit low-noise operating band of the nonpolar IMPATT diode is increased from 159.2 GHz to 184.3 GHz,183.4 GHz to 245.7 GHz,and 212.2 GHz to 285.6 GHz.The analysis shows that the mechanism comes from the excellent negative differential mobility characteristics in the nonpolar wurtzite GaN material and the excellent negative resistance generation ability in the nonpolar IMPATT diode.The IMPATT diode based on nopolar orientation wurtzite GaN can maintain a good unity between RF power and noise performance,it can improve the stability of the IMPATT diode in the terahertz frequency band and increase the tunability of the IMPATT diode.3.The influences of n-type doped GaN deep level defects on the DC and RF characteristics of GaN-based Schottky barrier IMPATT diodes are studied.The RF characteristics of IMPATT diode are seriously attenuated with the increase of the density of deep level defects due to the charge generated by the deep-level defects.Based on the research on the internal electron,energy band and electric field distribution and degradation mechanism of IMPATT diode,a double avalanche termination region structure(DATR)IMPATT diode is proposed to reduce the adverse effects of n-type doped GaN deep level defects.Finally,the negative peak conductance of the improved diode is 11.4×10~3 S/cm~2 at 248 GHz,showing the lowest quality factor of 1.42,the improved maximum power of 1.35 MW/cm~2 and efficiency of15.7%at 220 GHz under the same deep level defects density,these characteristics of the improved DATR structural IMPATT diode reach the level which the low deep level defects density original diode shows.4.A novel lateral Schottky barrier high-low IMPATT,the HEMT-like IMPATT(HIMPATT)diode is proposed based on the Al GaN/GaN 2-DEG and reactive ion etching(RIE)techniques.Numerical simulation demonstrated that comparing with the vertical IMPATT diode,the optimum frequency of HIMPATT diode rises from 260 to 380 GHz,the maximum RF output power rises from 2.30 to 3.06 MW/cm~2 and the maximum conversion efficiency rises from 14.7%to 18.5%.Simulation results reveal that the trench length L_r and depth D_rof 2-DEG channel significantly influence the output performances of HIMPATT diode,where the frequency characteristic is more sensitive to the trench length L_r and the RF power characteristic is more sensitive to the trench depth D_r.By designing the pattern shape of the trench area,a monolithic integrated HIMPATT diode oscillator array can be implemented on one chip to generate wider frequency band with great RF performances than the vertical IMPATT diode.