Electrical Properties Of The Dielectric Oxide / Gan-based Semiconductor Heterostructures

As a third-generation semiconductor, GaN-based semiconductors show many advantages, such as wide band gap, favorable thermal conductivity, high carrier drift velocity, high breakdown field, and so on. At the same time, oxide dielectric materials exhibit good electronic properties, such as well insulativity, ferroelectric polarization, and so forth. So the integration of oxide dielectrics with GaN semiconductors could be applied in new-type semiconductor devices with multifunction, excellent performance and high integration. However, there are some ticklish problems when integrating. The electrical properties of the device are not satisfied and the physical mechanism is not well understood. So, in this paper, by numerical simulation, the mechanism of the ferroelectric polarization modulation and the effect of the interface on the electrical properties of the heterostructure are discussed. Based on these, the electrical characteristics of oxide dielectric films and the performance of the integrated structure are studied. The main work and results are as following:1. The model of electrical property simulation of oxide dielectrics/GaN semiconductor heterostructure is built. The distribution of the heterostructure's potential and carriers are obtained by solveing the self-consistent Schr?dinger-Poisson equation; The effect of the interface on the electrical properties of the heterostructure is discussed by taking parameters such as interface thickness, dielectric constant and trap density into account in the electric displacement equation. Importantly, the unsaturated ferroelectric polarization is considered during the simulation of the heterostructure using the Lue ferroelectric polarization model.2. The simulations of oxide dielectrics/n-GaN heterostructure are carried out, including the effect of ferroelectrical polarization and interface characteristics on the heterostructure. The simulation results indicate that the ferroelectrical polarization could enhance the depletion of the carriers in the semiconductor and the control of the gate. At the same time, the switchable ferroelectric polarization could modulate the carriers in GaN. It also shows that the modulation capability of the ferroelectrical polarization is weakened with thicker interface, smaller dielectric and higher trap density. By the simulation of LiNbO₃/GaN, it is found that the ferroelectrical polarization of LiNbO₃ reaches 2.6μC/cm²,and the electron density at the GaN surface after poling is eight orders of magnitude higher than that after depoling, which manifests that the integration of LiNbO₃ with n-GaN would hold promise for non-volatile ferroelectrical memories.3. The accurate parameters of AlGaN/GaN template are obtained by C-V simulation, which lays the foundation of the simulation of oxide dielectric/AlGaN/GaN heterostructure. The parameters are: the thickness of AlGaN d_AlGaN=23nm, the doping concentration of AlGaN layer N_AlGaN<1×10¹⁶/cm³, the doping concentratin of GaN layer 1×10¹⁵/cm³, the polarization charge density at the AlGaN/GaN interface NP=9.7×10¹²/cm², the surface barrier hight SBH=1.3eV.4. The electrical property of the heterostructure of Al₂O₃/AlGaN/GaN is studied in this paper. By the simulation of the electrical property, it is found that the change of oxygen pressure is to change the negative charge density at the Al₂O₃/AlGaN interface, then reduce the sheet electron concentration of 2DEG in the semiconductor.5. The simulations of oxide dielectric/AlGaN/GaN heterostructure are carried out, the main work are done about the effect of ferroelectrical polarization and interface characteristics on the heterostructure. The simulation results indicate that the two-dimensional electron gas in AlGaN/GaN could be modulated effectively by the switchable ferroelectric polarization. It also shows that the modulation of the ferroelectrical polarization can be weakened with thicker interface, smaller dielectric and higher trap density. The simulation results of LiNbO₃/AlGaN/GaN heterostructure demonstrate that the polarization of LiNbO₃ reaches -0.5μC/cm² at a negative gate voltage and the two-dimensional electron gas density changes 7×10¹²/cm² with the effect of ferroelectrical polarization.