Performance of Devices Made of Large Band-gap Semiconductors, SiC and GaN




Okayama, Taizo

Journal Title

Journal ISSN

Volume Title



Silicon (Si) and gallium arsenide (GaAs) devices have limitations for certain applications such as high-power and/or high-frequency due to their material properties. As a partial fulfillment of the requirements for the degree of doctor of philosophy in electrical and computer engineering, devices made using two promising substrate materials: silicon carbide (SiC) and gallium nitride (GaN) were studied for high-power and high-frequency applications, respectively. The SiC is considered as a suitable material for high-power devices such as double-implanted metal-oxide-semiconductor field-effect-transistor (DMOSFET), in which the current flows vertically to the substrate contact. The DMOSFET consists of several hundred cells connected in parallel, making it possible to sustain both high blocking voltage and high current. GaN grown on SiC is considered as a suitable material for high-frequency and high-power applications. High electron mobility transistor x (HEMT) fabricated with GaN and aluminum gallium nitride (AlGaN) utilizes a conduction band offset and piezoelectric polarization effect at the junction between these two materials to produce a highly conductive channel. However, in spite of their promises, the performance of both SiC DMOSFET and GaN HEMT devices, with respect to their Si and GaAs counterparts are not well understood. In this work, first the SiC DMOSFET devices were characterized for their threshold voltage, drain current and breakdown voltage stability and then GaN devices for their efficiency and linearity performance at high-frequency. The results of SiC DMOSFETs were fitted with simulation to determine the location of the interface charge responsible for instability in device behavior. The charge at the inner region of the junction termination extension has the most pronounced effect on the breakdown voltage instability. The interlayer dielectric (ILD) composition that can minimize the SiC DMOSFET instability problem is also determined considering several limitations on the maximum weight percentages of the boron and phosphorous constituent dopants in the boro-phospho-silicate glass (BPSG) ILD layer. The BPSG with a composition of 2.4 weight percent B and 5 weight percent P is projected as optimum for the processing conditions used for making the SiC DMOSFET of this study. Results of GaN HEMTs were compared with those of GaAs pseudomorphic HEMTs.



SiC, GaN, Wide bandgap, Traps, High power