Effects of acceptors in a Fe-doped buffer layer on breakdown characteristics of AlGaN/GaN high electron mobility transistors with a high-kpassivation layer

We analyze off-state breakdown characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) with a Fe-doped buffer layer where a deep acceptor located above the midgap is included. It is shown that by introducing a high- k passivation layer, the breakdown voltage V br improves as in a case with an undoped semi-insulating buffer layer. In the Fe-doped case, V br becomes a little higher in the case where the passivation layer's relative permittivity ε r is rather higher when the energy levels determining the Fermi level are set equal in the two buffers. It is also shown that when the energy level of deep acceptor is deeper, V br becomes higher in the region where ε r is high. This occurs because the leakage current via the buffer layer becomes smaller.