Comprehensive modeling of the extrinsic transconductance for InxGa1-xAs/In0.52Al0.48As quantum-well high-electron-mobility transistors

Abstract

This paper presents the comprehensive modeling of extrinsic transconductance (gm_ext) in the saturation regime for InxGa1-xAs/In0.52Al0.48As quantum-well (QW) high-electron-mobility transistors (HEMTs) with Lg from 10 μm to sub-100 nm, covering the ballistic and mobility relevant regimes. First, we fabricated and characterized two types of lattice matched (LM) channel In0.53Ga0.47As QW HEMTs on a 3-inch InP substrate. One of these was fully fabricated with an i-line stepper, yielding Lg from 10 μm to 0.5 μm, and the other was fabricated in a mix & match manner with a combination of an i-line stepper and an e-beam lithography equipment, where T-shaped gates were implemented using a tri-layer resist stack of ZEP520A-PMGI-ZEP520A in the e-beam lithography process. Using devices with a wide range of Lg values, we examined the transconductance (gm) characteristics in saturation and attempted to correlate them to analytical expressions capable of describing the carrier transport properties of the devices using only physical parameters, such as the gate capacitance (Cgi) apparent mobility (μn_app), and saturation velocity (vsat), and the series resistances (Rs and Rd). In this way, we assessed the dependences of the extrinsic transconductances of the fabricated devices on their gate lengths, with the model parameters of Cgi = 0.65 μF/cm2, μn_app = 9400 cm2/V⋅s, vsat = 4.3 × 107 cm/s and Rs = 147 Ω⋅μm. These values were observed to be well-matched with those of the physical parameters. Most importantly, we extended the proposed approach to realistically project the increase in gm_ext that could be accomplished by improving certain device parameters.