Comparative studies of double δ-doped InAlAs/InGaAs metal-oxide-semiconductor metamorphic high electron mobility transistors (MOS-MHEMTs) with different compressive-strained and tensile-strained channel structures have been made. In addition to the strain engineering of the heterostructure, the MOS-gate design is also integrated by using the cost-effective H 2 O 2 oxidization technique. The tensile (compressive)-strained channel is devised by the In 0.52 Al 0.48 As/In 0.41 Ga 0.59 As (In 0.52 Al 0.48 As/In 0.63 Ga 0.37 As) heterostructure. Device characteristics with respect to different channel structures are physically studied. The impact-ionizationrelated kink effects in MHEMTs are significantly suppressed by the MOS-gate. Atomic force microscopy (AFM) and low-frequency noise (LFN) analysis were used to study the surface roughness and interface quality. As compared to the compressive-strained MOS-MHEMT and conventional Schottky-gate devices, the present tensile-strained MOS-MHEMT design has demonstrated improved transconductance gain (g m ), current drive, intrinsic voltage gain (A V ), and power performance. InAlAs/InGaAs MHEMTs have demonstrated advantages of large wafer-size and high electron mobility with respect to pseudomorphic high electron mobility transistors (pHEMTs) 1,2 and latticematched HEMTs on InP substrates. 3,4 It is because that the In-rich InGaAs channel can be grown on a robust GaAs substrate by the graded In x Al 1-x As metamorphic buffer (MB) design. Nevertheless, the impact-ionization-related kink effect 5 usually occurs in MHEMTs. This would seriously degrade gate leakage current, static power dissipation, and power-added efficiency (P.A.E.). Studies of strain engineering in the III-V research field have been made. 6,7 Channel engineering has been applied to form tensile-strained or compressivestrained HEMTs.8 The tensile-strained channel design has also been successfully used to effectively improve the carrier mobility in Sibased devices. A simple and cost-effective H 2 O 2 oxidization technique has been proposed in our previous work. 24 Therefore, this work investigates double δ-doped InAlAs/InGaAs MOS-MHEMTs based on strain engineering of the AlGaAs/InGaAs heterostructure and MOS-gate design by using the cost-effective H 2 O 2 oxidization method. Surface and interfacial property of the MOS-gate structure are studied by using AFM and LFN spectra. Device characteristics with respect to different strain mechanisms and Schottky/MOS-gate structures are physically investigated. Material Growth and Device FabricationThe schematic device structures of the studied InAlAs/InGaAs MHEMTs and MOS-MHEMTs grown by a MBE system are shown in Figs. 1a-1d. Upon the semi-insulating (S.I.) GaAs substrate, the epitaxial layers consist of a 5000-Å In x Al 1-x As MB layer, a 1500-Å undoped In 0.52 Al 0.48 As buffer, a Si δ-doped (n + = where a sc /a ch are the lattice constants of the Schottky-contact layer/channel. The lattice constant of the In x Ga 1-x As compound can be approximated by 25 a I nGa As = ...