Dependence on channel potential structures of I–V characteristics in InAlAs/InGaAs pseudomorphic high electron mobility transistors

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Abstract
We have systematically examined the relationship between channel potential structures and dc device performances in the InP-based pseudomorphic high electron mobility transistors, in order to obtain a guideline for improving the channel potential structures. Based on the self-consistent calculation of the quantum states in the channel, we have designed and fabricated several pseudomorphic devices with different channel potential structures where the quantum states were systematically changed. By comparing the I–V characteristics in terms of the transconductance, the drain conductance, and the shape of the I–V curve, we have successfully extracted information on the states of channel electrons under actual device operation. Not only the design for the ground state but also that for the excited states has been shown to be important for improving the transconductance. The drain conductance was shown to improve by reducing the total channel thickness, probably due to the enhanced recombination of electrons and holes. One of the channel designs, 20 Å In0.53Ga0.47As/30 Å InAs/70 Å In0.7Ga0.3As, was shown to yield a high transconductance of 1240 mS/mm and a low drain conductance of 40 mS/mm simultaneously, for a 0.7 μm gate length device.