Study On The Lateral Compositional Inhomogeneity Scattering Mechanism Of InAIN/GaN Heterostructure

A two dimensional electron gas(2DEG)with a high sheet carrier density and a high mobility can form in GaN-based heterostructures without intentionally doping,which shows the great potential of GaN-based heterostructures in high-power,high-frequency electronic devices in the form of high electron mobility transistors(HEMTs).In this thesis,the scattering mechanism due to the lateral compositional inhomogeneity(LCI),which widely exist in the InAIN/GaN heterostructures,are studied based on the perturbation theory and Boltzmann transport theory.The study of this thesis is directed towards developing a better understanding in the experimental observations and predicting the performance potential of InAlN/GaN HEMTs.The main results were summarized as follows:A new scatting mechanism due to LCI,i.e.conduction band fluctuation scattering,was proposed and the theoretical model is derived.The dependences of the conduction band fluctuation scattering on the structure parameters were calculated and compared vsith the subband energy fluctuation scattering.The results show that the conduction band fluctuation scattering-limited mobility decreases with increasing InAIN thickness,while the subband energy fluctuation scattering-limited mobility increases with the InAIN thickness.The two scattering mechanisms limited mobilities both decrease with increasing standard deviation of In mole fraction,and initially decrease and subsequently increase with increasing correlation length of In mole fraction.The effects of Al mole fraction of the AlGaN interlayers in InAIN/AlGaN/GaN heterostructures on three scattering mechanisms related to the InAIN layer,i.e.alloy disorder scattering,subband energy fluctuation scattering and conduction band fluctuation scattering were studied.The results show that in a small Al mole fraction range around 0.1,the alloy disorder scattering is the dominant scattering mechanism,while the subband energy fluctuation scattering dominates the mobility beyond this compositional range.When Al mole fraction is above 0.52,these scattering mechanisms-limited mobility exceeds that in the InAlN/GaN heterostructure without the AlGaN interlayer,indicating the promotion of the mobility by the AlGaN interlayer.The HEMT device simulation is performed with the Silvaco TCAD.The effects of LCI scattering mechanism and Al mole fraction of AlGaN interfacial layer on the DC output characteristics and transfer characteristics of InAlN/GaN HEMT devices are studied.The results show that the subband energy fluctuation scattering decrease the drain saturation current and increase the threshold voltage,while the conduction band fluctuation scattering is negligible.The increase of the Al mole fraction of AlGaN interfacial layer can effectively increase the drain saturation current and decrease the threshold voltage.