Spatial Wavefunction-Switched (SWS) InGaAs FETs with II–VI Gate Insulators

Abstract

This paper presents the implementation of a novel InGaAs field-effect transistor (FET), using a ZnSe-ZnS-ZnMgS-ZnS stacked gate insulator, in a spatial wavefunction-switched (SWS) structural configuration. Unlike conventional FETs, SWS devices comprise two or more asymmetric coupled quantum wells (QWs). This feature enables carrier transfer vertically from one quantum well to another or laterally to the wells of adjacent SWS-FET devices by manipulation of the gate voltages (V g ). Observation of an extra peak (near both accumulation and inversion regions) in the capacitance-voltage data in an InGaAs-AlInAs two-quantum-well SWS structure is presented as evidence of spatial switching. The peaks are attributed to the appearance of carriers first in the lower well and subsequently their transfer to the upper well as the gate voltage is increased. The electrical characteristics of a fabricated SWS InGaAs FET are also presented along with simulations of capacitance-voltage (C-V) behavior, showing the effect of wavefunction switching between wells. Finally, logic operations involving simultaneous processing of multiple bits in a device, using coded spatial location of carriers in quantum well channels, are also described.

Sequential Logic Circuits Using Spatial Wavefunction Switched (SWS) FETs

“…The peak seen in the C-V characteristics shows the transfer of electrons from well 2 to well 1 [6]. having two quantum wells can be seen in Fig 4(a).…”

“…The accumulation region shows the presence of two threshold voltages corresponding to the two quantum wells. "The peak on the left (at approximately -3.2V) is due to the holes first appearing in the lower well W2 and subsequently transferring to the upper well W1 as we move away from threshold towards accumulation" [6]. Fig4(b) shows the C-V plot for a different InGaAs two-well sample (#1965).…”

“…InGaAs which has carrier mobility higher than that of Silicon is used in the SWSFET configuration to provide faster switching feature in the device [6].…”

“…Different logic states are assigned to the device according to the current levels in the channels. So the device provides four states 00, 01, 10, 11 corresponding to the wavefunction being OFF (00), in well W2 (01), in Well 1 (10) and in both wells W2-W1 (11) [6]. The state assignments can be used in the implementation of efficient logic circuits.…”

“…Chapter 2 introduces the SWSFET device that was first developed and patented by Jain et al illustrating the two well and four well structures along with the quantum mechanical simulations [6]. The transfer of charge between wells, channel charge density and experimental capacitance voltage characteristics are shown in this chapter.…”