Study On Crystallization Quality And Electrical Properties Of Nearly Lattice-matched InAIN/GaN Materials

With the continuous development of GaN-based electronic materials and devicestowards higher frequency and higher power, the potential shortage of conventionalAlGaN/GaN heterostructure materials has been shown. Because of the misfitdislocations caused by lattice-mismatch between AlGaN and GaN buffer. InAlN barrierwith an indium concentration of18%has been attracting much attention, because it canbe grown lattice-matched with GaN showing a stress-free state and could avoid theproblems caused by lattice-mismatch. In nearly lattice-matched InAlN/GaN materialshigh density electrons(>2×10¹³cm^-2is induced in the GaN-channel with onlyspontaneous polarization effect present, When about1nm AlN interlayer is introducedbetween InAlN and GaN layers, the electron mobility significantly increases（>800cm2/Vs）and typical two dimensional electron gas（2DEG） conductance appears.However, the transport properties of InAlN/GaN materials and the improvementmechanisms of the electron mobility caused by AlN interlayer have not been studieddeeply. What’s more, the crystallization quality divergence among different samplesand the dispersion of experimental data make this research quite difficult. In this paper,we studied the crystallization quality and electric properties of InAlN/GaN andInAlN/AlN/GaN materials grown by pulse-MOCVD by theoretical and experimentalmethods comprehensively. The major research work and results are listed as following:1. The band diagram and carrier distribution of InAlN/GaN and InAlN/AlN/GaNmaterials were simulated by solving self-consistently Schr dinger’s and Poisson’sequations considering quantum effects. It was given the effects on the banddiagram and carrier distribution of Indium concentration, InAlN barrier thicknessand AlN interlayer thickness. It was found out that InAlN/AlN/GaN materials notonly induced higher2DEG density by spontaneous polarization but also hadstronger2DEG confinement at high temperature by comparing the band diagramand carrier distribution of InAlN/AlN/GaN and AlGaN/AlN/GaN hetero-structureswith same barrier thickness.2. It was shown the AlN interlayer effectively improved surface morphology andquality of the interface and decreased the defect density of InAlN barrier withexperimental investigation of structural properties of InAlN/GaN andInAlN/AlN/GaN materials by high resolution X-ray diffraction（HRXRD）, X-ray reflectivity（XRR）, Atom force microscopy（AFM） and Raman scattering etc.,3. The C-V and Hall measurements indicated that AlN interlayer not only increasedthe2DED density of InAN/GaN materials but also significantly improved the2DEG mobility. At300K, the Hall electron density is1.65×10¹³cm^P-2and1.75×10¹³cm^-2for InAlN/GaN and InAlN/AlN/GaN materials, respectively. TheHall mobility is949cm²/Vs and1437cm2/Vs. At77K, the Hall mobility ofInAlN/GaN and InAlN/AlM/GaN materials reaches2032cm2/Vs and5308cm²/Vs,respectively.4. Quantitative theoretical analysis of the temperature dependent mobility data of theaforementioned InAlN/GaN and InAlN/AlN/GaN materials was carried out basedon a comprehensive anylytical model including various scattering mechanismssuch as acoustic deformation-potential scattering, piezoelectric scattering, polaroptic phonon scattering, dislocation scattering, alloy disorder scattering andinterface roughness scattering. It was found that the electron mobility ofInAlN/GaN materials was improved because AlN interlayer eliminated the alloydisorder scattering of the InAlN barrier layer to2DEG and smoothed the interfaceand therefore restrained the interface roughness scattering.5. It was studied further with the above mobility model the correlation between2DEG mobility and2DEG density of nearly lattice-matched InAlN/GaN andInAlN/AlN/GaN materials based upon a wide collection of experimental data. Thetheoretical2DEG mobility as a function of2DEG density at room temperature wascalculated in a range of interface roughness values considering the difference ofsamples. It was found that the InAlN/AlN/GaN has smoother interface.