Typical Field-effect Device Charge Control Model Research

One of the core mechanisms of field effect (FE) devices modeling, charge controlmodel describes the variation of carriers charge density with gate voltage. Now, chargecontrol modeling of FE devices can resort to two methods: threshold voltage-based(VTH-based) model and surface potential-based (s-based) model, in which the former,owing to some historical factors, has been dominating in FE device modeling. With thedevelopment of microelectronic science and technology, devices dimensions becomesmaller together with stronger quantum mechanical (QM) effects, so much emphasishas been put on compact modeling, which means using uniform mathematical formulasto represent the characteristics of devices from accumulation region to strongly inverseregion. Accurately describing the device properties in subtreshold region, nowVTH-based model with compact form and clear physics attracts public concern againMOS structures and semiconductor heterojunction structures are two typical FEdevices. Applied most widely in applications, the research on MOS structures has beena key field in Microelectronics. As for heterojunction structures, the devices based onthe third generation semiconductor material GaN, due to its high electron mobility,good voltage withstand and thermoresistance, has become study hotspotIn this thesis, the charge control modeling technology regarding MOS andAlGaN/GaN heterojuction structures are investigated from the perspective of devicephysics. The main content can be divided into following parts:1. The research progresses of present international and domestic VTH-basedmodels have been summarized, and the related problems have been demonstrated.2. The charge distribution at semiconductor interface (surface) has been discussedunder semi-classical conditions and QM conditions. A perturbation-based method tocalculate the ground state characteristics of2DEG has been reported, with betteragreement with numerical solution than variational method. The accuracy of thismethod proves that it can be used in device modeling.3. VTH-based ands-based modeling methods of MOS devices have beenintroduced respectively. As a semi-QM correction, the degenerate effect of surface charge in inverse (accumulation) layer has been incorporated ins-based model ofMOS structures. The gate capacitance deduced from the proposed model achievesbetter agreement with experimental data than the result from the non-degenerate model,which indicates effectiveness and availability.4. The structure and working principle of AlGaN/GaN heterojunction-baseddevices has been introduced. Based on linear Taylor expansion, an analytical linearcharge control model of AlGaN/GaN heterojunction has been developed at thepresence of temperature variable. Without any numerical iteration involved, theparameters of the model under different temperatures are determined by a set ofanalytic expressions, with enough accuracy. Based on the proposed charge controlmodel, an analytic thermal DC output characteristic has been worked out underfield-induced-velocity mechanism. At last, this thermal DC I-V model is employed toinvestigate the self-heating in AlGaN/GaN HEMT with two kinds of substrates:sapphire and SiC.With enough accuracy and practical applicability, the research fruits of the thesispromise to provide references and guides for device modeling.