Study On InAs/AlSb High Electron Mobility Transistor

Due to high electron mobility,high electron saturation velocity,and high 2DEG sheet density in the channel,InAs/AlSb HEMT has become one of the most promising candidates for high-speed,low-power,and low-noise applications.In this thesis,InAs/AlSb HEMT is studied from various perspectives and the following results are obtained.The simulation platform of InAs/AlSb HEMT is established though Sentaurus TCAD.DC and AC characteristics of devices with 250 nm gate length are simulated.Saturation drain current Id,SS,and peak transconductance gm are 768 mA/mm,140 mV/dec,and 1942 mS/mm,respectively,at Vds=0.4 V.Furthermore,the cut off frequency ft and maximum oscillation frequency fmax of the simulated device are 199 GHz and 489 GHz,respectively.This simulation result indicates the superiority of this device.The device fabrication process of InAs/AlSb HEMT are explored and designed.Key processes such as ohmic contact,mesa isolation and Schottky gate formation are studied in detail.Ohmic contact is formed by e-beam evaporating Pd/Ti/Pt/Au(20/30/30/30 nm),following by RTA 300 ? for 20 s.The contact resistance R,and contact resistivity ?c are 0.116 ?·mm and 3.50× 10-7?·cm2,respectively though TLM.Mesa isolation is performed by the use of RIE dry etching with Ar/Cl2/CH4.Before Schottky gate metal deposition,gate recess is formed by a citric acid/H2O2 solution in order to avoid gate-to-source and gate-to-drain conduction because of the highly doped InAs cap layer.Then,Schottky gate metal is deposited by e-beam evaporating Ti/Pt/Au(20/20/300 nm)and lift off.Finally,devices with Lg=?2 ?m,W=2×50 ?m,and LSD=-8 ?m are fabricated.DC characteristic indicates that the device has excellent carrier transport property.However,its electrostatic control is not acceptable.The ultimate solution to suppress the high gate leakage current in InAs/AlSb HEMT is to insert high-k dielectric between InAlAs and gate metal.Thus,MOS-HEMT is developed.DC and AC characteristics of MOS-HEMT are simulated and compared with HEMT.Id,SS,and gm are 822 mA/mm,181 mV/dec,and 1876 mS/mm,respectively,at Vds=0.4 V Moreover,ff and fmax of the simulated device are 292 GHz and 403 GHz,respectively.High-k/InAlAs MOS structure is the key part of MOS-HEMT.Therefore,the conduction mechanisms of Al2O3/InAlAs MOS structure are analyzed in detail.Experimental results indicate that Schottky emission is dominant at forward bias.And the extracted dielectric constant of Al2O3 and Schottky barrier height between Al2O3 and InAlAs are 8.09 and 0.6±0.01 eV.Schottky emission is also dominant at low reverse bias and the extracted dynamic dielectric constant of Al2O3 and Schottky barrier height between Al2O3 and gate metal are 1.64-2.86 and 0.70±0.01 eV.However,I-V characteristics fit well with SCL conduction at medium and high reverse bias.TFL conduction is observed at all the measurement temperatures,whereas Ohm's law is only observed at 343 K and transition between TFL conduction and Child's law is only observed at 323 and 343 K.This phenomenon could be ascribed to different transition conditions at different measurement temperatures.Besides,the potential well depth of traps(Ec-Et)calculated from TFL conduction is 0.401±0.01 eV.