Research On Heterogeneous Integrated InP-based Terahertz HEMT Device

Due to frequency range of terahertz wave,terahertz wave has the characteristics of large communication capacity,low photon energy,large frequency bandwidth,small diffraction effect,strong penetration,and excellent beam directionality,thus,it has a broad application prospects in mobile communication systems,satellite communication systems,phased array radar,high-definition imaging in agriculture,medical,and security,non-destructive detection of organisms,atmospheric imaging detection,and other fields.On the other hand,Heterogeneous integration technology can integrate III-V compound semiconductor devices with frequencies up to the terahertz band onto silicon-based circuits,greatly expanding the application range of silicon-based circuits.It can not only improve the high-frequency and low noise performance of silicon-based circuits,but also take advantage of the low cost and high reliability advantages of silicon-based circuits.Based on the above situation,this article studies the device structure design and device process of InP based HEMT devices heterogeneously integrated on silicon.The main research content is as follows:1.Using Slivaco TCAD software as the platform,we modeled InP based HEMTs and simulated and analyzed structural parameters such as In Al As barrier layer thickness,δ-planar doping concentration of the doping layer,and In Al As spacer layer thickness.Taking into account the requirements of high transconductance,high current output density,high breakdown voltage,and high cutoff frequency,the device structure with the best comprehensive performance of 12nm In Al As barrier layer thickness,5×10¹²cm^-2plane doping concentration,and 3nm In Al As spacer layer was ultimately selected as the reference structure for subsequent simulation and experiments in this article.2.Based on the established InP based HEMT reference device structure,the structure is heterogeneously integrated onto a silicon substrate and interface charges are introduced at the wafer bonding interface.The structure is simulated using Silvaco software.In the simulation model,this article gradually increases the surface density of negative interface charges from-5×10¹⁰cm^-2to-5×10¹¹cm^-2.Through simulation calculations,the device transfer characteristics,threshold voltage,output characteristics,C-V characteristics,leakage current,energy band,carrier concentration,carrier mobility,channel electric field,cutoff frequency,delay time,and other performance changes caused by changes in charge surface density were studied and analyzed.Research has found that negative interface charges can limit the distribution of charge carriers in the channel,leading to a decrease in electron concentration and a positive shift in the transfer curve.The peak transconductance,output current density,and cutoff frequency of the device decrease,while the breakdown voltage shows an upward trend.At the same time,the charges at three interfaces were compared,and the charge at the InP/Si O2 interface had the greatest impact on the device.3.According to the InP based HEMT reference structure,an InGaAs/InP（u）/InP（n）composite channel structure was composed of InP sub-channels and In_0.53Ga_0.47As channels.We first studied the effects of InP（n）doped secondary channel layer thickness on device transfer characteristics,threshold voltage,output characteristics,C-V characteristics,energy band,carrier concentration,carrier mobility,channel electric field,gate leakage current,channel collision ionization rate,thermal characteristics,cut-off frequency,delay time,and other performance through simulation analysis.As the thickness of the InP（n）doped sub-channel layer decreases,although the peak transconductance,output current density,and cutoff frequency of the device all decrease,they are still higher than the conventional InGaAs channel HEMT,at the same time,the breakdown characteristics of the device have been significantly improved.Based on this,the article proposes doped InP sub-channel structures and undoped InP sub channel structures,and compares and analyzes the device characteristics of these structures with conventional singleδ-doped InGaAs and doubleδ-doped InGaAs channel structures.Under the condition of ensuring the same level of output current and cutoff frequency,both types of InP sub channel structures improve the device’s breakdown characteristics,with the undoped InP sub channel structure having the highest breakdown voltage.4.Based on the above InGaAs/InP composite channel HEMT device structure,an InP epitaxial wafer with inverted structure HEMT was designed,and material characterization and surface morphology testing were conducted on the epitaxial wafer.The HEMT epitaxial layer structure was positively transferred to the silicon substrate through wafer bonding and InP substrate corrosion processes.After the film transfer was completed,non-contact Hall testing was performed on the heterojunction film to obtain its electron mobility,carrier concentration,and block resistance.The reason for its performance degradation was compared with the pre transfer epitaxial film and analyzed.After the transfer of heterojunction thin film,we designed the device layout,process structure,and process flow,fabricated InGaAs/InP composite channel HEMT on silicon,and conducted DC and AC tests.The Ohmic and Schottky contacts of the device were good,and the leakage current of the mesa isolation reached the expected level.However,due to the decrease in film quality,especially the decrease in effective carrier mobility,the device’s output current density and cutoff frequency exhibit significant performance degradation compared to HEMT on conventional InP substrates.Based on the measured effective electron mobility,carrier concentration,and gate metal work function used in the process,the model in the previous simulation was modified.After calibration,the model is basically consistent with the actual measured characteristic curve,which can accurately simulate the various characteristics of InP based HEMT heterojunction on silicon.