Design and fabrication of double modulation dopedInAlAs/lnGaAs/InAs heterojunction FETs for high-speed andmillimeter-wave applications

We report the design, fabrication, and characterization of InP-based double-sided-doped (DSD) MODFETs with InAs-layer-inserted channels. Devices based on optimized structures show a significant improvement in the effective saturation velocity, from 2.4×10⁷ cm/s for lattice-matched MODFETs to 3.1×10⁷ cm/s for InAs MODFETs. This leads to a maximum extrinsic transconductance of 1.95 S/mm and excellent high-speed performance of f_T=265 GHz for 0.13-μm T-gates. A f_max higher than 300 GHz can be achieved by fabricating a wide lateral recess groove, which simultaneously results in an improved breakdown voltage of 6.7 V. The excellent RF performance is primarily due to the reduction of Coulomb scattering from donor layers, especially under the channel, and to the reduction of scattering caused by the interface roughness. This improvement is achieved by inserting a 4-nm InAs layer, which better confines the two-dimensional electron gas (2DEG) at the center of the channel of MODFET's