The effects of carbon on the bidirectional threshold voltage instabilities induced by negative gate bias stress in GaN M
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The effects of carbon on the bidirectional threshold voltage instabilities induced by negative gate bias stress in GaN MIS‑HEMTs Nicolò Zagni1 · Alessandro Chini1 · Francesco Maria Puglisi1 · Paolo Pavan1 · Giovanni Verzellesi2 Received: 7 May 2020 / Accepted: 8 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this paper, numerical device simulations are used to point out the possible contributions of carbon doping to the threshold voltage instabilities induced by negative gate bias stress in AlGaN/GaN metal–insulator–semiconductor high-electron mobility transistors. It is suggested that carbon can have a role in both negative and positive threshold voltage shifts, as a result of (1) the changes in the total negative charge stored in the carbon-related acceptor traps in the GaN buffer, and (2) the attraction of carbon-related free holes to the device surface and their capture into interface traps or recombination with gate-injected electrons. For a proper device optimization of carbon-doped MIS-HEMTs, it is therefore important to take these mechanisms into account, in addition to those related to defects in the gate dielectric volume and interface which are conventionally held responsible for threshold voltage instabilities. Keywords GaN power devices · Threshold voltage instability · Negative gate bias stress · NBTI · Carbon doping
1 Introduction GaN technology has eventually found its way to the power electronics market [1, 2], thanks to the lower total losses at higher breakdown voltage and higher switching frequency allowed by GaN-based transistors compared to Si power devices [3]. While normally-off devices, either based on the junction-gated high-electron mobility transistor (HEMT) (aka p-GaN HEMT) or the fully recessed gate metal–oxide–semiconductor field-effect transistor (MOSFET) concepts are intensively being developed at both research and industry levels [1, 2], the two-chip cascade connection of a low-voltage Si MOSFET with a highvoltage, normally-on AlGaN/GaN metal–insulator–semiconductor high-electron mobility transistor (MIS-HEMT) still represents a commonly adopted solution mainly for its * Nicolò Zagni [email protected] 1
Department of Engineering “Enzo Ferrari”, University of Modena and Reggio Emilia, Via P. Vivarelli 10, 41125 Modena, Italy
Department of Sciences and Methods for Engineering (DISMI), EN&TECH Center, University of Modena and Reggio Emilia, Via G. Amendola 2, 42122 Reggio Emilia, Italy
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compatibility with Si drivers [1]. Concerning the substrate material for the GaN device, a large-area Si wafer is the solution of choice for cost competitiveness [1, 2]. Given the insulated gate structure of the MIS-HEMT, threshold voltage (VT) stability is a major concern critically impacting yield [4]. For normally on devices with negative threshold voltages of several volts, VT stability after the application of a large and negative gate bias is, in particular, a key aspect that needs careful evaluation during technology deve
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