InP-based HEMTs with AlIn/sub 1-x/P Schottky barrier layers grown by gas-source MBE

Abstract

We report on the performance of a new class of InP-based HEMTs in which the conventional Al/sub x/In/sub 1-x/As Schottky barrier layer is replaced with Al/sub x/In/sub 1-x/P. 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/sub gd/) of <-5 V reported for Al/sub 0.48/In/sub 0.52/As/GaInPLs HEMTs limits the device performance for high power applications. A significant research effort has concentrated on improving BV/sub gd/ by increasing the aluminum concentration in the AlInAs layer. An increase in BV/sub gd/ from -5 V to -10 V has been achieved in our laboratory by increasing the aluminum concentration in the Al/sub x/In/sub 1-x/As Schottky layer from x=0.48 to x=0.70. Other researchers have reported BV/sub gd/ as high as -13 V for an In/sub 0.4/Al/sub 0.6/As/n+-InGaAs HFET with a gate length of 1.9 /spl mu/m. These breakdown voltages are, however, still much lower than typical values of BV/sub 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/sub 0.52/In/sub 0.48/P barrier layer has been reported with BV/sub gd/ of -17 V and -10 V for 1.0 and 0.1 /spl mu/m long gate devices, respectively. More recently, a pseudomorphic channel InP HEMT with an Al/sub 0.2/In/sub 0.8/P barrier was reported with a BV/sub gd/=-15 V for a gate length of 0.5 /spl mu/m. In this paper, we present for the first time the performance of a Al/sub x/In/sub 1-x/P/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/sub 0.6/In/sub 0.4/As/Al/sub 0.48/In/sub 0.52/As/Ga/sub 0.47/In/sub 0./$ d5/sub 3/As HMT to illustrate the improved device characteristics with the AlInP barrier layer.<>