InGaAs Inversion Layer Mobility and Interface Trap Density From Gated Hall Measurements

In this letter, we use gated Hall method for direct measurement of free carrier density and electron mobility in inversion InGaAs MOSFET channels. At room temperature, the highest Hall mobility of 1800 cm²/Vs is observed at electron density in the channel $\approx 1\times 10^{12}$ cm $^{-2}$ . A comparison with mobility values estimated from transistor characteristics reveals a significant underestimation of mobility, which arises from overestimation of channel density obtained from $C$ – $V$ measurements. Temperature dependence of the electron mobility provides the evidence that remote Coulomb scattering dominates at electron density $< 3\times 10^{11}$ cm $^{-2}$ . Contrary to the capacitance-based methods commonly used for extraction of interface trap density, a gated Hall method can separate the contributions of fast-trapped charges and free carriers in the channel to the total charge of a MOS capacitor. This allows for reliable estimation of trap density at the III–V/high- $k$ interface including border traps. The results illustrate that even high-quality interfaces providing high-mobility transport suffer from fast border traps above the conduction band. In contrast with Si where the effect of border traps is negligible, in low density-of-state InGaAs channel material as much as half of the channel electrons can be trapped and excluded from transport, increasing switching energy and dissipated power.

I. Introduction

Group III-V semiconductors are potential candidates for replacement of Si channel for complimentary metal-oxide-semiconductor (CMOS) logic applications because of. their high carrier mobility. However, reduction of electron trap density at high-k oxide/III-V interface is still the major challenge for III-V device technology in sub 10nm nodes [1], [2]. Conventional characterization methods primarily based on admittance measurements are unable to unambiguously determine interface trap density ( [3]–[8]; in particular, they cannot distinguish between free carriers and trapped carriers with fast response. In addition, III-V materials have low density of conduction band states and relatively high density of border traps [9], [10] that can have very fast (up to GHz) response [11] contributing to C-V measurements even under strong inversion conditions in contrast with Si MOS structures. Conventional methods employing a combination of C-V and I-V characteristics to estimate the effective mobility in the channel [5], [6], [12]–[15] result in over-estimation of channel charge thereby leading to under-estimation of carrier mobility. In this work, we use a gated Hall method to find the mobility and in an In_0.53Ga_0.47As inversion channel. Gated Hall method [12], [16]–[19] extracts without assumption of the trapping rates and the mobility is obtained from the Hall/conductivity measurements. Previously, we used gated Hall method to extract and mobility in buried InGaAs channels [17]–[19].