InAlAs/InGaAs HFET with extremely high device breakdown using an optimized buffer layer structure

InAlAs/InGaAs heterostructure field-effect transistors (HFET´s) grown on InP show excellent RF and noise performance because of the large conduction-band discontinuity and the high electron mobility. However, these devices suffer from low breakdown voltage, high output conductance and small voltage gain. Furthermore, the growth start on InP in molecular-beam epitaxy (MBE) systems with arsenic overpressure is a sophisticated technology which may result in an additional interface charge and inferior buffer layer quality. Much effort has been paid to the development of high resistive buffers with smooth transitions to the channel. The impact of low temperature (LT) growth was first studied at very low growth temperatures (Tg=150...200°C). It has been shown that the highest specific resistance of MBE grown InAlAs is achieved even at higher substrate temperatures (T_g=350...420°C). In this work we provide a detailed experimental study of the buffer influence on the DC and RF performance of MBE grown InAlAs/InGaAs HFETs. After optimization of the growth start on InP substrates, the influence of the buffer layer design such as InGaAs/InAlAs superlattices (SL) and quaternary pseudomorphic GaInAlAs/InAlAs-SL is evaluated. Special care was taken on the realization of high mobility samples incorporating an InAlAs buffer, grown at a moderate low temperature (T_g=420°C)