Molecular-beam epitaxial growth of InAs/GaAs superlattices on GaAs substrates and its application to a superlattice channel modulation-doped field-effect transistor

The molecular-beam epitaxial growth conditions for (InAs)m(GaAs)n short period superlattices (SPSs) on GaAs substrates have been optimized by monitoring reflection high-energy electron diffraction (RHEED) intensity oscillations. The RHEED oscillation measurements enable understanding InAs growth behavior on a 7% lattice-mismatch GaAs substrate. Within one monolayer InAs deposition with lower than 560 °C growth temperature can give high SPS crystalline quality. The SPS periodic structure and the monolayer InAs formation, embedded in GaAs layers, have been confirmed by x-ray diffraction and transmission electron microscopy measurements. The obtained thickness controllability for the SPSs is less than±6% for InAs and ±3% for GaAs. The electron Hall mobilities for modulation-doped structures having an (InAs)1(GaAs)n SPS as an electron channel, whose layer index of n varied from 3 to 6, have been compared with those with a pseudomorphic InGaAs random alloy channel which has the equivalent In composition. The SPS channel samples have shown up to 15% higher electron Hall mobilities than the InGaAs alloy channel samples at 77 K. A 0.2-μm-gate (InAs)1(GaAs)6 superlattice channel modulation-doped field-effect transistor (FET) has exhibited a maximum extrinsic transconductance of as high as 450 mS/mm with a 70-GHz cut-off frequency at room temperature. The best noise figure of 0.58 dB with an associated gain of 11.15 dB has been attained. The obtained device characteristics are comparable or superior to those for the corresponding InGaAs alloy channel FETs. These results demonstrate, for the first time, the (InAs)m(GaAs)n SPS potentialities as an ordered counterpart for InGaAs random alloy for high-speed device applications.