Analysis of buffer-impurity and field-plate effects on breakdown characteristics in small-sized AlGaN/GaN high electron mobility transistors

Abstract

The two-dimensional analysis of breakdown characteristics in field-plate AlGaN/GaN high electron mobility transistors with a relatively short gate length and short gate-to-drain distances is performed by considering a deep donor and a deep acceptor in a buffer layer. It is shown that when the acceptor density in the buffer layer is high, the breakdown voltage is determined by the impact ionization of carriers, and it can decrease with increasing the field-plate length. This is because the distance between the field-plate edge and the drain becomes very short and the electric field there becomes very high. On the other hand, when the acceptor density in the buffer layer is relatively low, the buffer leakage current becomes very large and this can determine the breakdown voltage, which becomes very low. In this case, the breakdown voltage increases with increasing the field-plate length.

Similarities of lags, current collapse and breakdown characteristics between source and gate field-plate AlGaN/GaN HEMTs

“…We use our in-house software, and the details on the basic equations and physical parameters are given in our previous works [14], [19]. We use drift-diffusion-type equations, and treat an iso-thermal case [13], [19].…”

Analysis of breakdown characteristics in source field‐plate AlGaN/GaN HEMTs

“…1) enhances the power performance of AlGaN/GaN HEMTs [3][4][5]. This is because the introduction of field plate reduces the current collapse [6][7][8], and increases the off-state breakdown voltage [9][10][11]. Usually, the breakdown voltage increases with increasing the fieldplate length [9], because the electric field at the drain edge of the gate decreases.…”

“…The deep acceptor's energy level is set 0.6 eV above the top of valence band. The deep donor's energy level is typically set to 0.5 eV below the bottom of conduction band [11]. As values of the deep-acceptor density N DA , we consider a case with high N DA of 10 17 cm -3 .…”

“…Basic equations to be solved are Poisson's equation including ionized deep-level terms, continuity equations for electrons and holes including a carrier generation rate by impact ionization and carrier loss rates via the deep levels [11,17]. These are expressed as follows:…”

“…G is the carrier generation rate due to impact ionization, and is given by (4) where α n and α p are ionization rates for electrons and holes, respectively, and expressed as (5) (6) where E is the electric field. A n , B n , A p , and B p are deduced from [18], as in [11]. Figure 2 shows calculated drain current I D -drain voltage V D curves and gate current I G -V D curves of source field-plate AlGaN/GaN HEMTs when the gate voltage V G is − 8 V, which corresponds to an off state.…”