Electrical Performance And Stability Of High Mobility And Narrow Band-gap Semiconductors Transistors

By now,the silicon complementary metal-oxide-semiconductor(CMOS)technology has been pushed down to 7 nm by Moore's Law.More and more challenges are emerging while the scaling of the silicon devices is finally approaching its fundamental limits.Making smaller and faster Si transistors for microprocessors is becoming a huge challenge.Non-Si channel materials with high mobility and narrow band-gap are expected to have better electric performance.InGaAs,black phosphorus(BP),and germanium(Ge)are all narrow bandgap semiconductors with high mobility,which are the promising channel materials candidates for high speed and low power CMOS devices.However,it also poses many challenges and long-standing problem is passivation of the defects between deposited gate insulators and channel materials,which severely degrade the electrical performance and stability of the devices.In this thesis,we systematically study the electrical performance and stability of transistors based on narrow band-gap semiconductors with high mobility,such as bulk germanium,two dimensional BP,quasi-1D indium gallium arsenide(InGaAs)nanowire.The mainly results are shown below:1,Ge CMOS devices with recessed channel and source/drain(S/D)are thoroughly studied.Benefited from the balanced carrier mobilities of Ge and well-engineered gate-stacks,the Ge nMOSFETs and pMOSFETs show near-symmetrical performance.Ge CMOS devices and circuits with various channel lengths from 10 to 90 nm are comprehensively studied in terms of device characteristics nMOSFETs and pMOSFETs with near symmetrical performance.Good voltage transitions are achieved in the CMOS inverters with a wide range of supply voltage(V_DD),from 1.6 to 0.2 V.We also report bias temperature instability(BTI)measurement on both Ge nMOSFETs and pMOSFETs and observe that Ge pMOSFETs threshold voltage shifts to the opposite direction comparing with classic NBTI phenomenon in silicon.A simple model is proposed to explain the experimental observation.The stability of Ge CMOS inverter under AC signal is also studied.It is found that Ge CMOS inverter has certain current stability and voltage instability after long-term operation.2,The few layers BP is a novel high mobility 2D material.Because ultra-thin black phosphorus layers degrade rapidly in ambient atmosphere,the primary work of making BP devices is studying and stopping this degradation.We thoroughly investigate BP oxidation and discuss the reaction mechanism based on the X-ray photoelectron spectroscopy(XPS)data.BP oxidation was characterized after different treatments in 5%O₂/Ar,2.3%H₂O/Ar,and 5%O₂&2.3%H₂O/Ar at 20°C.The XPS results show water accelerates the oxidation through the reaction with surface oxide and by this creating the sites for oxygen dissociation.The BP few-layer field-effect transistor(FET)with a 0.8 nm Al protecting layer has presented a better device performance than the one that is directly deposited with Trimethylaluminium and water.Similarly,h-BN passivation also helps retain good transport properties of BP.The results provide the guidance to preserve the BP sample in water-free environment.Atomic layer deposition(ALD)integration using water-free precursors deposition ALD dielectric passivation or h-BN passivation formed in a glove-box environment are also presented.3,We show the key fabrication processes for InGaAs gate all around(GAA)quasi-1D nanowire MOSFETs,and carried out electrical measure of the InGaAs GAA FETs under various temperatures form 300 K to 4.3 K to fully understand the basic physics mechanism of III-V materials.First,we study the temperature dependence for devices on-state and off-state performance.Then we study the temperature dependent subthreshold characteristics,such as threshold voltage,drain induced barrier lowering and subthreshold slope.We also analyze the intrinsic device parameters,including contact resistance and effective channel mobility under different temperatures.Finally,the low-frequency noise of quasi-1D InGaAs nanowire transistors is measured and the noise mechanism of those devices is studied,the results show the 1/f noise of the device mainly comes from the contact resistance.