Study Of GaN MOSFET Device

As one of the third generation semiconductor maerials, Gallium Nitride (GaN) has some semicondutor features, such as lare direct bandgap, high saturation drift velocity, large conduction band discontinuities, high thermal stability and strong piezoelectric and spontaneous polarization. GaN has been widely used for high frequency, high power electric devices and photoelectric devices for its good physical and chymic characteristics.Recent progress in AlGaN/GaN Heterostructure Field Effect Transistors (HFETs) has demonstrated that many question related to the material quality such as defect states and trapping effects in a heterostructure and following device performance reliability are still open. And there has been great interest in development of GaN based metal-oxide-semiconductor (MOS) transistors because of their lower leakage currents and power consumption relative to the common GaN high electron mobility transistor (HEMT) devices. However, there are many problems still badly restrict improving performance of the GaN MOS devices such as high interface state density of the gate dielectrics or low electron mobility of the invension channel or difficulty in obtaining p-doped substrate.The characteristics of GaN MOSFET has been discussed in this paper using the method of computer simulation. The contains and results as follows: 1. Simulate DC characteristics of GaN MOSFET at room temperature, analysis relationship between the transfer characteristics and output characteristics and the key parameters, such as oxide thickness, gate length, channel doping concentration, dielectric constant. The results show that GaN MOSFET requires that gate length is relatively long, and 2μm is the crucial point of hort-channel effect. When the gate dielectric permittivity is high, the device transfer characteristics and output characteristics are greatly improved. GaN MOSFET device which is used undoped-GaN as epitaxial layer has been simulated, when analyzing the impact of substrate doping concentration for device characteristics. In short, we can select the appropriate structural parameters in order to obtain better characteristics of GaN MOSFET. 2. Analysis transfer characteristics and output characteristics of the device, when temperature varies from 300K to 800K. We conclude that the DC characteristics of devied worsen, and the decay of mobility and saturation drift velocity is the main reason. 3. Analysis the different structure GaN MOSFET devices. The p type GaN material is the key factor for the development of GaN MOSFET, so we select 2μm undoped-GaN as epitaxial layer. And then grow 100nm GaN of doping concentration 1×1017cm-3 as channel layer. We analysis characteristics of this depletion-mode GaN MOSFET. 4. Do some experiments on the characteristics of GaN MOSFET. We obtain the threshold voltage is about 4V, the drain saturation current is 3.2mA, when VGS=10V. And we simulate the same structure device using ATLAS. Experimental result and simulation result are compared. Two results have some differences because of the interface state density and the quality of the GaN material which are currently restricted mainly the development of GaN MOSFET.