Buffer‐trapping effects on drain lag and power compression in GaN FET

Abstract

PACS 71.55.Eq, 72.20.Jv, 85.30.De, 85.30.Tv Buffer-trapping effects in a GaN MESFET are studied by two-dimensional transient simulation. A threelevel compensation model is adopted for a semi-insulating buffer layer where a shallow donor, a deep donor and a deep acceptor are considered. It is shown that when the drain voltage V D is raised, the drain current overshoots the steady-state value, and when V D is lowered, the drain current remains at a low value for some periods, showing drain lag behavior. This drain lag is shown to become a cause of so-called power compression in the GaN MESFET.

Reduction of buffer‐related current collapse in GaN FETs under favour of a field plate

“…In both cases, the drain currents remain at low values for some periods ("quasi-steady state") and begin to increase slowly, showing drain-lag behavior. It is understood that the drain currents begin to increase when the deep donors in the buffer layer begin to emit electrons [6,7]. The current rise time is roughly consistent with the deep donor's electron-emission time constant (given by inverse of the electron emission rate), which becomes 9.8x10 3 s for E C −E DD = 1.0 eV.…”

“…The shallow-donor density N Di is set to 10 15 cm -3 . When N DD > N DA , the deep donors donate electrons to the deep acceptors, and hence the ionized deepdonor density N DD + becomes nearly equal to N DA under equilibrium, and it acts as an electron trap [6,7].…”

“…Surface states are not considered to concentrate on buffertrapping effects. As a model for a semi-insulating buffer layer, we use three-level compensation model which includes a shallow donor, a deep donor and a deep acceptor [6,7]. Some experiments show that two levels (E C -1.75 eV, E C -2.85 eV) are associated with current collapse in GaN-based FETs [1], and hence we use energy levels of E C -2.85 eV (E V + 0.6 eV) for the deep acceptor and of E C -1.75 eV for the deep donor.…”

Analysis of buffer‐trapping effects on current collapse of GaN FETs

“…These are serious problems, and there are many experimental works reported on these phenomena [1][2][3][4][5]. But, only a few theoretical works have been reported recently for GaN-based FETs [5][6][7], although several numerical analyses were made for GaAsbased FETs [8][9][10][11]. In a previous work [7], we made primary two-dimensional simulation of a GaN MESFET on a semi-insulating buffer layer in which a deep donor and a deep acceptor are considered and showed that the drain lag and the current collapse could be reproduced.…”

“…But, only a few theoretical works have been reported recently for , although several numerical analyses were made for GaAsbased FETs [8][9][10][11]. In a previous work [7], we made primary two-dimensional simulation of a GaN MESFET on a semi-insulating buffer layer in which a deep donor and a deep acceptor are considered and showed that the drain lag and the current collapse could be reproduced. In this work, we have made more systematic simulations of GaN MESFETs on the semi-insulating buffer layer and studied how the current collapse is affected by impurity densities in the buffer layer and by an applied drain bias.…”