Physical Mechanism of Buffer-Related Current Transients and Current Slump in AlGaN/GaN High Electron Mobility Transistors

Abstract

Two-dimensional transient analyses of AlGaN/GaN high electron mobility transistors (HEMTs) are performed in which a deep donor and a deep acceptor are considered in a buffer layer. Quasi-pulsed current-voltage (I-V) curves are derived from the transient characteristics. When the drain voltage is raised abruptly, electrons are injected into the buffer layer and captured by deep donors, and when it is lowered abruptly, the drain currents remain at low values for some periods and begin to increase slowly as the deep donors begin to emit electrons, showing drain-lag behavior. The gate lag could also occur due to deep levels in the buffer layer, and it is correlated with relatively high source access resistance in AlGaN/GaN HEMTs. It is shown that the current slump is more pronounced when the deep-acceptor density in the buffer layer is higher and when an off-state drain voltage is higher, because the trapping effects become more significant. The drain lag could be a major cause of current slump in the case of higher off-state drain voltage. It is suggested that to minimize current slump in AlGaN/GaN HEMTs, an acceptor density in the buffer layer should be made low, although there may be a trade-off relationship between reducing current slump and obtaining sharp current cutoff.

Simulation of Deep-Level Trap Distributions in AlGaN/GaN HEMTs and Its Influence on Transient Analysis of Drain Current

“…TCAD modeling efforts using commercial tools at replicating transient behavior of unintentionally doped GaN (UID-GaN) generally adopt the three-level compensation model. 18,21 In this model, the transient aspect is contributed only by a single deep donor.…”

“…TCAD modeling efforts using commercial tools at replicating transient behavior of unintentionally doped GaN (UID-GaN) generally adopt the three-level compensation model. 18,21 In this model, the transient aspect is contributed only by a single deep donor.The introduction of a single discrete deep-level, while being sufficient to qualitatively simulate dynamic I-V curves and bias dependence of trap occupancy in the bulk, cannot successfully replicate current relaxation curves observed during transient analysis. To this end, introduction of multiple deep trap levels will be necessary to obtain curves with multiple relaxation time constants observed in experiments.…”

Analysis of Parasitic Effects in AIGaN/GaN HEMTs

“…However, the types of traps and their energy levels seem to be artificial. Therefore, in this article, we have made two-dimensional transient simulations of AlGaN/GaN HEMTs with a buffer layer in which trap levels based on experiments are considered, as in our previous work on GaN MESFETs (Horio et al, 2005), and showed that the lag phenomena and current collapse could be reproduced (Horio & Nakajima, 2008). Also, we have studied dependence of current collapse on the impurity densities in the buffer layer and on an off-state drain voltage.…”

Reduction of buffer‐related current collapse in field‐plate AlGaN/GaN HEMTs

“…This is called current collapse in the GaN device field. These are serious problems, and many experimental works have been made [1][2][3][4][5][6][7], but only a few theoretical works are reported [7][8][9]. It is shown that the gate lag and current collapse can be reduced by SiN surface passivation [3] and by using a field plate [5].…”

“…In our previous works [8,9], we made twodimensional transient simulation of GaN MESFETs and AlGaN/GaN HEMTs in which deep levels in a semiinsulating buffer layer were considered, and showed that the lag phenomena and current collapse could be reproduced. In this work, we have made two-dimensional analyses of field-plate AlGaN/GaN HEMTs with deep levels in a buffer layer, and found that the buffer-related lag phenomena and current collapse could also be reduced by introducing a field plate.…”