Spacer design to improve the breakdown voltage of InAlAs-InGaAs HEMTs

The work presented in this paper shows that the use of a mixed InAlAs/InP spacer rather than a conventional InAlAs spacer considerably improves the breakdown voltage of the devices in taking advantage of the large valence band offset of the InP/InGaAs heterojunction (0.42 eV). Also, this structure is entirely lattice matched thus avoiding the growth problems associated with strained layers. Furthermore, the noise associated with this device has been shown to be lower than that of conventional AlInAs/GaInAs HEMTs thanks to the low defect concentration in InP as compared to InAlAs.