Heterogeneous Epitaxy Of High Mobility Materials Of ?-? Family And Its Application

The narrow band-gap materials of InAs,InSb and InAsSb in ?-? compounds not only have high electron mobility and electron saturation drift velocity,but also can form diverse quantum well band structures with AlSb,GaSb and related ternary broadband gap materials.The quantum well band structures can effectively confine carriers in the quantum well.These excellent performances make the electrical devices have the advantages of ultra-high speed and low power consumption,which are widely used in wireless high-frequency communication,military radar,portable mobile devices,vacuum detection and other fields.In this dissertation,the heteroepitaxial materials and devices of InAs,InSb and InAsSb have been investigated by theoretical analysis and experimental research.The main research and innovative achievements in this dissertation are as follows:?1?Theoretical analysis of high mobility heteroepitaxial materials and devices.The electron mobility in the quantum well structure has been calculated,included various scattering mechanisms.In particular,the effect of dislocation scattering on mobility was added.Secondly,the electrical properties of high mobility devices using InAs,InSb,and InAsSb as channel materials were simulated by the Sentaurus.As a result,at the V_D of 0.5V and V_G of 0 V,the saturation drain current of InAs,InSb,and InAsSb HEMT with 2?m gate length are 275 mA/mm,420 mA/mm and 352.49 mA/mm,respectively.It provides a theoretical basis for subsequent experiments.?2?Growth of InAs materials.?a?The two-step method and the off-angle Si substrate were used to solve the problems of lattice mismatch,thermal mismatch and anti-phase domain.The effects of growth temperature and annealing temperature on the electron mobility and surface morphology of Si-based InAs were investigated.The results show that the highest electron mobility is4640 cm²/V·s in the sample,in which the 10 nm InAs nucleation layer was grown at a low temperature of 320?followed by ramping up to 560?and the nucleation layer was annealed for 15 min.Then the second layer of InAs was grown at 520?.Secondly,it is found that the InGaAlAs metamorphic buffer layer with linear component gradient can significantly improve the electron mobility.At 300 K,the highest electron mobility of Si based InAs is 9222 cm²/V·s.?b?A GaAs-based AlSb/InAs quantum well heterostructure was prepared.The temperature dependence of electron mobility and the two-dimensional electron gas concentration in AlSb/InAs heterostructure for the temperature range 90 K³00 K has been investigated.The electron mobility in the quantum well at 90 K is 42560 cm²/V·s.?c?The step-graded GaAs_xSb_1-x-x metamorphic buffer layer and mobility enhancement method were used to improve the lattice mismatch,thermal mismatch and anti-phase domain between the Si substrate and the AlSb/InAs quantum well heterostructures.The influence of the growth temperature of the step-graded GaAs_xSb_1-x-x metamorphic buffer layer on the electron mobility and surface topography of the AlSb/InAs quantum well heterostructures grown on Si substrates has been investigated.Based on the measurements results,the composition of As in GaAs_xSb_1-x layer increases,while the peaks positions of GaAs_xSb_1-x change from GaSb to GaAs due to the different of sticking coefficient.The results show that the highest diffraction intensity of the HRXRD scan curve,the narrowest FWHM,the highest electron mobility of 10270 cm²/V·s and the RMS roughness of 4.3 nm,is observed for the step-graded GaAsxSb1_-x metamorphic buffer layer grown at a temperature of 410?.?3?Growth of InSb and InAsSb Material.?a?The growth temperature and V/III ratio of InSb films grown on GaAs substrate were optimized.It was found that the atomic steps can be clearly seen at the growth temperature of 420?and the V/III ratio of 6,indicating that the surface morphology is the best.The highest electron mobility at room temperature is 38860 cm²/V·s.?b?The straddle energy band structure of Al_0.2In_0.8Sb/InAs_0.4Sb_0.6 heterostructure is used to replace the interleaved energy band structure of InAs/AlSb heterostructure,which can effectively reduce the lattice mismatch and the gate leakage current caused by holes.The effects of metamorphic buffer layer,channel layer width,Sb composition,spacer layer width and Si?-doping density on the transport properties and crystal quality of Al_0.2In_0.8Sb/InAs_0.4Sb_0.6 heterostructures were studied.The scattering mechanisms of interface roughness scattering,dislocations scattering,polar optical phonon scattering,remote impurity scattering,alloy scattering and inter-subband scattering have been discussed to examine their effect on electron mobility and 2DEG concentration.The results show that the highest electron mobility of 28300 cm²/V·s and 2DEG concentration of9.28×10¹11 cm^-2 at 300 K are obtained in the unintentionally doped Al_0.2In_0.8Sb/InAs_0.4Sb_0.6heterostructures.Meanwhile,the electron mobility of 26500 cm²/V·s,2DEG concentration of 1.15×10¹22 cm^-2 at 300 K and RMS roughness of 0.68 nm can be achieved in the Al_0.2In_0.8Sb/InAs_0.4Sb_0.6 modulation-doped heterostructures with a 30 nm channel,a 6 nm spacer layer width and a 9.0×10¹⁸cm^-3 Si?-doped layer.The RMS roughness is 0.68 nm.Compared with the previous reports,the higher electron mobility,better surface morphology and flatter channel interface of the Al_0.2In_0.8Sb/InAs_0.4Sb_0.6 heterostructures with the Sb component of 0.6 have been achieved in this dissertation,which can be used to prepare high electron mobility transistors.?4?Fabrication of high-electron-mobility transistors.The fabrication process of HEMT was designed,in which the process is based on four main processing steps:ohmic contact,mesa isolation,gate metal electrode deposition and probing pad metallization.The AlSb/InAs and Al_0.2In_0.8Sb/InAs_0.4Sb_0.6 HEMTs were fabricated.The test results show that the AlSb/InAs HEMT device performance is significantly improved with 27%lower gate leakage current,12%higher maximum drain current and 22.5%higher peak transconductance at 90 K compared to 300 K.The I_D of the AlSb/InAs HEMT with the SiO₂ passivation increases from 160 mA/mm to 214 mA/mm and the maximum I_D of simulation is 275 mA/mm at the V_D of 0.5 V and the V_G of 0 V,which is close to the result of theoretical simulation.At the same bias voltage,the maximum drain current of Al_0.2In_0.8Sb/InAs_0.4Sb_0.6 HEMT is significantly higher than that of AlSb/InAs HEMT devices.