Alternatives for Doping in Nanoscale Field‐Effect Transistors

Abstract

In the present article, alternatives to impurity doping in nanoscale field‐effect transistors (FETs) are investigated. The discussion is based on conventional and tunnel FETs. The impact of dopant deactivation due to dielectric mismatch or quantization, random dopant effects, and the degeneracy level on the performance is discussed. As alternatives metal‐semiconductor‐contacts, gate‐controlled doping and an interface engineering approach are studied. One of the main requirements for proper device functionality is the existence of a band gap in the contacts. Thus, metal‐semiconductor contacts are less suited since they lead to ambipolar operation with increased leakage and to a deteriorated on‐state performance. With gate‐controlled doping, electrodes areused to create doped regions leaving behind a pristine band gap. Moreover, it enables reconfigurable devices with nFET, pFET and tunnel FET operation. Furthermore, with multiple nanoscale gates, electrostatic doping allows manipulating the potential within the device on the nanoscale. Experimental demonstrations of such devices with triple‐gates and multiple gate structures are presented. Finally, the interface engineering approach allows combining a metallic contact electrode with an almost unmodified band gap in the source/drain contacts by adjusting an ultrathin insulator in‐between metal and semiconductor yielding quasi‐doped contacts whose polarity depends on the work function of contact metal.

The concept of electrostatic doping and related devices

“…Hueting et al [10] present the theory of electrostatic doping induced by metal workfunction or gate bias as well as the physics of Schottkybarrier devices, including their charge plasma diode [8]. The role of electrostatic doping in TFETs and reconfigurable multi-gate MOSFETs is discussed by Knoch et al [11]. In this paper, we review the state of the art of electrostatic devices from a different angle.…”

Remote free-carrier screening to boost the mobility of Fröhlich-limited two-dimensional semiconductors

“…VdWh engineering brings particularly interesting opportunities to electronic transport. High-mobility semiconductors are useful in many devices, especially when coupled with electrostatic doping [11][12][13], which allows one to explore a wide range of carrier densities in a nondestructive and versatile way. In this context, depending on the application and the situation, the operating layer needs to perform well in many different doping regimes (hereafter, the nature of the doping should be understood as electrostatic).…”

Towards electrostatic doping approaches in ultra-thin body semiconductor materials and devices

“…One potential solution to doping problem in thin-film poly-GaN films for device applications could be the electrostatic doping (ED) [17,[45][46][47][48] approach where charge carriers are induced in the ultra-thin body semiconductor by using a suitable metal work function or by applying a gate bias. ED has already been demonstrated in various material systems and device geometries where conventional doping is otherwise challenging, as discussed in the next chapter.…”

“…For more detailed overview on ED based innovative FD-SOI devices, please refer to [48]. Further, for a more technology focused review on ED based TFETs and reconfigurable FETs refer to [47].…”

“…For detail discussion on performance, technological aspects and merits of various potential ED-based devices for future CMOS, please refer to[46][47][48].…”