InP-based HEMTs with AlIn1-xP Schottky barrier layers grown by gas-source MBE

We report on the performance of a new class of InP-based HEMTs in which the conventional Al_xIn_1-xAs Schottky barrier layer is replaced with Al_xIn_1-xP. The study of alternative Schottky barrier designs is aimed at improving the performance of InP-based HEMTs for applications that require high breakdown voltages, such as microwave power amplifiers. The typical low gate-to-drain breakdown voltage (BV_gd) of <-5 V reported for Al_0.48In_0.52As/GaInPLs HEMTs limits the device performance for high power applications. A significant research effort has concentrated on improving BV_gd by increasing the aluminum concentration in the AlInAs layer. An increase in BV_gd from -5 V to -10 V has been achieved in our laboratory by increasing the aluminum concentration in the Al_xIn_1-xAs Schottky layer from x=0.48 to x=0.70. Other researchers have reported BV_gd as high as -13 V for an In_0.4Al_0.6As/n+-InGaAs HFET with a gate length of 1.9 μm. These breakdown voltages are, however, still much lower than typical values of BV_gd>20 V reported for GaAs MESFETs and HEMTs. In addition, the increased Al concentration may limit both device reliability and yield due to poor gate metal adhesion to the Al-rich layer. Phosphorous containing materials are an attractive candidate for a wide bandgap Schottky layer design with low aluminum content. A pseudomorphic GaAs-based HEMT with Al_0.52In_0.48P barrier layer has been reported with BV_gd of -17 V and -10 V for 1.0 and 0.1 μm long gate devices, respectively. More recently, a pseudomorphic channel InP HEMT with an Al_0.2In_0.8P barrier was reported with a BV_gd=-15 V for a gate length of 0.5 μm. In this paper, we present for the first time the performance of a Al_xIn_1-xP/AlInAs/GaInAs HEMT in which the channel is lattice matched to the InP substrate. We compare the performance of this new device with an Al_0.6In_0.4As/Al_0.48In_0.52 As/Ga_0.47In_0.$ d5₃As HEMT to illustrate the improved device characteristics with the AlInP barrier layer