Submicron pseudomorphic double heterojunction InAlAs/In0.7 Ga0.3As HEMTs with high cut-off and current-drive capability

Lattice-matched and strained (pseudomorphic) InAlAs/InGaAs high electron mobility transistors (HEMTs) are recognized as the most suitable components for operation at millimeter-waves. Pseudomorphic InAlAs/In_xGa_1-xAs (x>0.53) HEMTs are particularly promising candidates for high-frequency and low-noise applications due to the superior material properties of the strained InGaAs channel. The InGaAs channel with excess indium provides improved low-field mobility characteristics, better carrier confinement and higher peak velocity due to the larger Γ-to-L valley separation, compared with lattice-matched channels. The authors address such pseudomorphic designs using double heterostructure (DH) HEMT designs. They demonstrate the possibility of combining pseudomorphic rather than lattice-matched channels with a double heterostructure design to optimize the frequency and current drive characteristics of DH-HEMTs. The DC and microwave characteristics of the fabricated submicron DH-HEMTs are presented and compared with single heterostructure (SH)-devices processed at the same time. Improved f_max and higher current density have been obtained with the pseudomorphic DH-HEMTs compared to SH-HEMTs