Impact of Gate and Passivation Structures on Current Collapse of AlGaN/GaN High-Electron-Mobility Transistors under Off-State-Bias Stress

Abstract

Previous results for the generation of linear, icosahedral, Jahn-Teller (JT) Hamiltonians with continuous group symmetries are extended. It is demonstrated that it is possible to define electronic generalized tensor operators on a direct sum electronic space such that a set of these operators is closed under commutation with another set of electronic generalized tensor operators which act as the generators of a continuous group. The normal modes carrying irreducible representations of the continuous group are then coupled 'equally' to produce a JT Hamiltonian which is invariant under the operations of the continuous group. The continuous groups generated on the direct sum spaces (T 1 ⊕ T 2 ), (T i ⊕ G), (T i ⊕ H ) and (G ⊕ H ) are discussed in detail. These additional continuous groups are of interest when the lowest JT states of certain icosahedral JT systems (such as some of those found in C 60 ) are modelled. The additional continuous group symmetry allows an analytic diagonalization of the linear JT matrix to be provided and thus facilitates an exact treatment of the vibronic ground state for these models.

DC and Pulse I–V Characteristics of Strain‐Engineered AlGaInN/GaN HEMTs fabricated on Single‐Crystal AlN Substrate

“…[29] In addition, from this result, we can construe that the current collapse observed for the unpassivated HEMTs was mostly related to the surface traps and thereby it was effectively suppressed by applying the ALD-Al 2 O 3 passivation. [23,24]…”

“…Then, the gate Schottky contacts were formed by evaporating a Pd/Ti/Au (40/20/60 nm) film. In addition, to apply them to the study on the drain-current collapse, the surface passivation with an Al 2 O 3 film [23,24] was adopted to fabricated devices. That is, after completing the previous procedure, a 15 nm thick Al 2 O 3 film was formed by an atomic layer deposition (ALD) at 300 °C and 0.35 Pa. [24] Then, the Al 2 O 3 film was partially removed by a wet etching to secure the contact paths.…”

Study of Current Collapse Behaviors of Dual-Gate AlGaN/GaN HEMTs on Si

“…On the other hand, a longer stress period allows depleted carriers to recover in the channel so that current collapse is less obvious. Among various methods to suppress current collapse, such as gate field plates [8], surface passivation [9], [17], dual-gate metal stacks [11]- [13], and HD-GIT [10], [20] as described in the Introduction Section, our results of demonstrating a normalized R ON of 1.87 (by applying V G_Aux of 0 V on G L (see Figure 5) at the stress condition V D _ OFF of 100 V and V G _ OFF of -10 V) are superior to most of previous works by taking the stress voltage and pulse period into consideration. Our approach avoids material regrowth, thus reducing the cost and improving the production yield.…”

“…The above reports, however, did not apply a bias voltage to the additional gate, mainly because of the concern of complicating the circuitry. To explore the physical root cause of current collapse, there were also reports using the additional gate to probe the surface trap distribution [16], [17].…”

Effects of p-GaN Capping Layer on the Current Collapse Behaviors in Normally-off p-GaN Gate AlGaN/GaN HFETs

“…A p-GaN barrier below the gate depletes the channel and increases the turn on voltage larger than 0V. Although, the p-GaN gate structure can make the AlGaN/GaN HFETs attractive for high-power applications by combining the high-mobility 2-DEG transistor channel with a secure normally-off operation, the current collapse effects related with surface and/or bulk traps are still critical problems which need to be overcome for the successful commercialization of AlGaN/GaN HFETs [2]. For a high-voltage Al-GaN/GaN HFET working at a switching mode, the current collapse effect always results in dynamic performance degradation, i.e., longer switch on delay time and higher dynamic ON-state resistance (R ON ), which increases the power consumption in the electrical energy conversion systems.…”