Delay Time Analysis of AlGaN/GaN Heterojunction Field-Effect Transistors with AlN or SiN Surface Passivation

Abstract

We have carried out delay time analysis for the high-frequency characteristics of AlGaN/GaN heterojunction field-effect transistors (HFETs) on sapphire substrates, focusing on a comparison between the effects of AlN and SiN surface passivation. HFETs with AlN passivation, in comparison with those with SiN passivation, exhibit high current gain cut-off frequencies f T with good flatness, in accordance with high intrinsic transconductance due to the self-heating reduction effect of AlN. From the delay time analysis, we find that the effective saturation electron velocity for AlN and SiN passivation is similar, while the electron mobility under the gate for AlN passivation is higher. This implies that the higher f T is mainly due to the higher electron mobility under the gate owing to the self-heating reduction by AlN passivation. This is consistent with the fact that the saturation velocity has a weak temperature dependence, while the mobility has a strong dependence.

Gate-control efficiency and interface state density evaluated from capacitance-frequency-temperature mapping for GaN-based metal-insulator-semiconductor devices

“…Owing to their high thermal conductivities, the nitride materials are favorable also for passivation of GaN-based devices, exhibiting good heat release properties. 4,[11][12][13][14][15] Since controlling insulator-semiconductor interfaces is critical for both gate-insulator or passivation applications, it is important to characterize and analyze the interface states. In fact, we observe frequency dispersion in C-V characteristics of MIS devices, attributed to electron trapping/detrapping at interface mid-gap states leading to gate-control impediment.…”

Low Dynamic ON-Resistance in AlGaN/GaN Power HEMTs Obtained by AlN Thin Film Passivation

“…The charging/discharging of these slow interface states under high electric field could lead to current collapse in AlGaN/GaN HEMTs under large drain bias. Thus, the nitride-based high-k dielectrics such as AlN emerges as a compelling candidate for passivation with low interface states for GaN-based devices (18)(19)(20)(21)(22)(23), because of its smaller lattice mismatch to GaN and larger bandgap (compared to SiN x ).…”

“…In situ metal-organic chemical vapor deposited (MOCVD) thin AlN films have been implemented as the gate dielectric in MIS-HEMTs (18,21). Thick AlN layer had also been deposited on AlGaN/GaN HEMTs by dc sputtering and used as the heat spreading layer, for devices on low-thermal-conductivity sapphire substrate (22,23). However, the possible surface damage induced by the high-energy sputtering ions makes the control of AlN/III-nitride interface and the consequent passivation a challenging task.…”

Application of Sputtering-Deposited AlN Films to Gate Dielectric for AlGaN/GaN Metal–Insulator–Semiconductor Heterojunction Field-Effect Transistor

“…6) Previously, sputtering deposition of AlN on AlGaN/GaN, in which we expect a more controllable interface, was applied to passivation of AlGaN/GaN HFETs. [7][8][9][10][11][12] The AlN-passivated HFETs exhibit good heat release properties due to the high thermal conductivity of AlN 13) ($10 times higher than that of Al 2 O 3 ), and also effective suppression of current collapse. Since AlN has a possible high breakdown field &10 MV/cm 14,15) and a high dielectric constant $10, 16) which are comparable to those of Al 2 O 3 , the sputtering-deposited AlN can be a favorable gate dielectric for AlGaN/GaN MIS-HFETs, with the merits of a more controllable interface and better heat release properties.…”