Abstract
Insulated-gate GaN-based transistors can fulfill the emerging demands for the future generation of highly efficient electronics for high-frequency, high-power and high-temperature applications. However, in contrast to Si-based devices, the introduction of an insulator on (Al)GaN is complicated by the absence of a high-quality native oxide for GaN. Trap states located at the insulator/(Al)GaN interface and within the dielectric can strongly affect the device performance. In particular, although AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) provide superior properties in terms of gate leakage currents compared to Schottky-gate HEMTs, the presence of an additional dielectric can induce threshold voltage instabilities. Similarly, the presence of trap states can be detrimental for the operational stability and reliability of other architectures of GaN devices employing a dielectric layer, such as hybrid MIS-FETs, trench MIS-FETs and vertical FinFETs. In this regard, the minimization of trap states is of critical importance to the advent of different insulated-gate GaN-based devices. Among the various dielectrics, aluminum oxide (Al2O3) is very attractive as a gate dielectric due to its large bandgap and band offsets to (Al)GaN, relatively high dielectric constant, high breakdown electric field as well as thermal and chemical stability against (Al)GaN. Additionally, although significant amounts of trap states are still present in the bulk Al2O3 and at the Al2O3/(Al)GaN interface, the current technological progress in the atomic layer deposition (ALD) process has already enabled the deposition of promising high-quality, uniform and conformal Al2O3 films to gate structures in GaN transistors. In this context, this paper first reviews the current status of gate dielectric technology using Al2O3 for GaN-based devices, focusing on the recent progress in engineering high-quality ALD-Al2O3/(Al)GaN interfaces and on the performance of Al2O3-gated GaN-based MIS-HEMTs for power switching applications. Afterwards, novel emerging concepts using the Al2O3-based gate dielectric technology are introduced. Finally, the recent status of nitride-based materials emerging as other gate dielectrics is briefly reviewed.
Highlights
Introduction iationsOwing to the large bandgap of 3.43 eV, resulting in a high electric breakdown field of 3.3 MV/cm and in a low intrinsic carrier concentration, and to the large saturation velocity of 2.5 × 107 cm/s, GaN is one of the most promising semiconductors for the future energy-efficient generation of high-power, high-frequency and high-temperature electronics [1,2,3,4]
A reduced off-state leakage current, in Figure 7, Ueda et al [192] very recently applied AlON films deposited by atomic layer deposition (ALD) com- a breakdown voltage of 730 V, an on-state bined to a postdeposition annealing (PDA) in O for shifting the V so to realize the normally off operation in the resistance of 270 mΩ for a 10 A drain current rating and impressive switching performance, recessed-gate AlGaN/GaN MIS-high electron mobility transistors (HEMTs), with a negligible hysteresis in the transfer characteristics, a reduced off-state leakage current, a breakdown voltage of 730 V, an on-state indicating the great potential of AlON as gate dielectric technology
We have summarized the most relevant challenges and recent progress on the development of a gate dielectric technology for insulated-gate GaN-based devices for high-frequency and high-power applications
Summary
MIS-FET with fully recessed (d) trench trench MISFET; (f) vertical FinFET. FET; (f) vertical FinFET. Stability the recentof status nitride-based materials emerging other thedielectrics gate leakage currents, gate is briefly reviewed.even at forward gate bias operation, a large bandg as well as large band offsets to (Al)GaN are necessary, in particular for powe devices. In the MIS-HEMTs, since the introduc consideration of the properties of the bandgap, thecase bandof offset to (Al)GaN, the permittivity and the chemical stability of the insulators. Gate-to-channel capacitance with of respect t the gate leakage currents, even at forward gate bias operation, a large bandgap material gate HEMTs, a high permittivity dielectric reduces the capacitive contribution as well as large band offsets to (Al)GaN are necessary, in particular for power switching dielectric, enabling it to obtain a stronger coupling between the gate and the 2 devices. Falabretti and by Reddy al. [57]
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