A Study Of Interface Characteristics In GaN-based Devices With SiNx Dielectric Grown By LPCVD

This thesis mainly focuses on the study of the interface characteristics in Ga N-based devices with Si N x dielectric grown by LPCVD. In order that a comprehensive knowledge or understanding of the interface quality of Si N x/Ga N in Ga N-based MIS or MISHEMT devices in terms of the physical mechanisms can be acquired, C-V electrical tests supported by I-V tests have been performed, followed by a quantitative characterization of the interface quality in Ga N-based devices using frequency dispersion, conductance and Terman method.First of all, C-V curves and energy band diagrams under various gate bias are simulated using Atlas device simulator from Silvaco Company in Ga N-based MIS or MISHEMT devices, to lay a good theoretical foundation for the associated analysis of some electrical behaviors in the C-V tests of Ga N-based devices.A variety of research methods of quantitative characterization of interfacial properties in Ga N-based devices have been compared and analyzed systematically in this thesis. For Ga N MIS devices, frequency dispersion, conductance and Terman method are employed for the extraction of interface state density D it, which is an important parameter in the quantitative characterization of the interface properties. As to Ga N MISHEMT devices, only frequency dispersion and conductance can be utilized since Terman method cannot apply to this case that Ga N MISHEMTs have two interfaces. It has been found that the D it values of frequency dispersion are the highest, conductance the lowest and Terman method in the middle. Since each research method or extraction method of D it has its own pros and cons, the extraction method of D it should be selected scientifically according to our actual test conditions and research goals.C-V and I-V tetsts are performed on two Si N x/Ga N MIS samples, in which Si N x dielectric is deposited firstly at 780? by LPCVD and then ohmic contacts are annealed at 650? or 830?. The analysis of C-V tests is mainly concentrated on the quantitative characterization of interfacial properties based on frequency dispersion, conductance and Terman method. All the results have shown that the sample annealed at high temperature features a higher D it with smaller current density and larger breakdown voltage than low temperature, which may be associated with Si dangling bonds and Si-H bonding as the extraction result of the trap depth from the Poole-Frenkel current revealed. Combined with the result of D it, it may be explained as follows: during annealing at high temperature the Si-H bonds at the interface will release H atoms leaving more Si dangling bonds, namely more interface states, thus causing a higher D it.Then the study of of interfacial properties in typical Ga N MISHEMT devices, in which Si N x dielectric is deposited firstly at 780? by LPCVD and then ohmic contacts are annealed at 830?, has been conducted. For the quantitative characterization of the interface quality, frequency dispersion and conductance method are utilized to extract D it. By conductance method, the Si N x/Ga N interface or heterojunction interface can be characterized respectively under different gate bias. The results show that D it of conductance is 2~3 orders of magnitude lower than that of frequency dispersion and that D it of Si N x/Ga N interface is one order of magnitude higher than that of heterojunction interface. Finally, pulse I-V tests are performed at three typical quiescent bias points(V GSQ,V DSQ)=(0,0)(-15 V,0)(-15 V,30V) in our Ga N MISHEMT devices. The interface state trap is a very important factor which can affect pulse I-V characteristics. By the comparison of output characteristics of pulse I-V at three quiescent bias points with that of DC I-V, the scientific explanation based on self-heating effect and traps' capture of electrons is given to further validate Si N x/Ga N interface of high quality in our Ga N-based devices with LPCVD-Si N x.In summary, this thesis has carried out a series of basic research and explorations about interfacial properties in Ga N-based devices with LPCVD-Si N x and achieved some original resluts in this initial stage. Moreover, the research will play an instructive role in the actual process flow and reliability analysis of Ga N-based devices.