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Influence of GaN- and Si 3 N 4 -Passivation layers on the performance of AlGaN/GaN diodes with a gated edge termination

Abstract:

This paper analyses the influence of the GaN and Si <inf>3</inf> N <inf>4</inf> passivation (or 'cap') layer on the top of the AlGaN barrier layer on the performance and reliability of Schottky barrier diodes with a gated edge termination (GET-SBDs). Both GaN cap and Si <inf>3</inf> N <inf>4</inf> cap devices show similar dc characteristics but a higher density of traps at the SiO <inf>2</inf> /GaN interface or/and an increase of the total dielectric constant in the access region result in higher R <inf>ON</inf> -dispersion in GaN cap devices. The leakage current at medium/low temperatures in both types of devices shows two low-voltage-independent activation energies, suggesting thermionic and field-emission processes to be responsible for the conduction. Furthermore, a voltage-dependent activation energy in the high-temperature range occurs from low voltages in the GaN cap devices and limits their breakdown voltage (V <inf>BD</inf> ). Time-dependent dielectric breakdown measurements show a tighter distribution in Si <inf>3</inf> N <inf>4</inf> cap devices (Weibull slope β = 3.3) compared to GaN cap devices (β = 1.8). Additional measurements in plasma-enhanced atomic layer deposition (PEALD)-Si <inf>3</inf> N <inf>4</inf> capacitors with different cap layers and TCAD simulations show an electric field distribution with a strong peak within the PEALD-Si <inf>3</inf> N <inf>4</inf> dielectric at the GET corner, which could accelerate the formation of a percolation path and provoke the device breakdown in GaN cap SBDs even at low-stress voltages.