Top-gating of p-Si/SiGe/Si inverted modulation-doped structures

Abstract

Low-temperature electrical properties of two-dimensional hole gases (2-DHGs) in Si/Si0.8Ge0.2/Si inverted modulation-doped structures have been investigated at different hole densities using a metal semiconductor gate sputtered on top of these structures. The 2-DHG which is supplied to the inverted interface of Si/SiGe/Si quantum well by a Si boron-doped layer spatially grown beneath the alloy, was controlled in the range of 1.5–7.8×1011 cm−2 hole density by biasing the top gate. With increasing 2-DHG sheet density, the hole wave function of these structures expands and moves away from inverted interface, consequently the mobility enhances. These results may be understood theoretically by elaborating the role of interface charge, roughness, and alloy scattering mechanisms in limiting the mobility of holes at the inverted interface.

Single-hole transistor in a p-Si/SiGe quantum well

“…Homogeneous top gating of this material has been reported as well. 5 In those samples, the two-dimensional hole gas ͑2DHG͒ is buried very deeply below the surface, which limits the pattern transfer into the 2DHG. The fabrication of any kind of gated nanostructure in p-Si/SiGe has not been reported yet.…”

Low-temperature electrical characterization of the Ti–Si(100) interface at the p-Si/SiGe/Si–Ti structure using Hall measurement analysis

“…The layer sequence of the epitaxially grown structure and charge distribution at low temperature in the absence of applied gate voltage are shown in figure 1(a). The growth details and device processing have been reported before [11]. As seen, 2DHG is located near the lower (inverted) interface of a compressively strained SiGe quantum well, while positive interface charges (metal-induced donor interface states) are accommodated at the Si-Ti interface.…”

“…It is necessary to mention that provided the leakage is negligible (here for V gc in the range of −0.7 V up to 2.4 V at 6 K), the Hall experiment can be conducted. Moreover, the gate should modulate (change) the 2DHG density n h as the gate-channel voltage switches to discrete values [11].…”

“…where ε is the permittivity of free space, ε r is the dielectric constant of a silicon semiconductor, e is the electron charge and L gc is the distance of the 2DHG and Ti gate electrode provided; the interfacial layer thickness δ (which is of the order of atomic distance) was neglected. As is customary, one can figure out the average distance of 2DHG from the lower interface (Z av = 3/b) [11] which is explained in the following, so we obtain…”

“…In this structure, a two-dimensional hole gas (2DHG) is formed in the SiGe quantum well buried beneath the final Si (cap) layer. It was demonstrated that the sheet density of 2DHG confined in this structure depends on the applied voltage to the Ti-Si Schottky gate with respect to the SiGe conduction channel [10,11]. Thus, it has been implemented in density dependence studies of the transport properties of 2DHG in Si/SiGe/Si quantum wells [12][13][14].…”