Carrier density modulation in a germanium heterostructure by ferroelectric switching

Abstract

The development of non-volatile logic through direct coupling of spontaneous ferroelectric polarization with semiconductor charge carriers is nontrivial, with many issues, including epitaxial ferroelectric growth, demonstration of ferroelectric switching and measurable semiconductor modulation. Here we report a true ferroelectric field effect-carrier density modulation in an underlying Ge(001) substrate by switching of the ferroelectric polarization in epitaxial c-axis-oriented BaTiO 3 grown by molecular beam epitaxy. Using the density functional theory, we demonstrate that switching of BaTiO 3 polarization results in a large electric potential change in Ge. Aberration-corrected electron microscopy confirms BaTiO 3 tetragonality and the absence of any low-permittivity interlayer at the interface with Ge. The non-volatile, switchable nature of the single-domain out-of-plane ferroelectric polarization of BaTiO 3 is confirmed using piezoelectric force microscopy. The effect of the polarization switching on the conductivity of the underlying Ge is measured using microwave impedance microscopy, clearly demonstrating a ferroelectric field effect.

A review of molecular beam epitaxy of ferroelectric BaTiO3films on Si, Ge and GaAs substrates and their applications

“…The in-plane and out-of-plane parameters were 3.987 Å and 4.040 Å respectively. Ponath et al [116] have grown c -axis BaTiO 3 films using a 2 nm SrTiO 3 buffer on Ge (with ½ ML Sr prior to the SrTiO 3 buffer growth). The lattice parameters were a = 3.96 Å and c = 4.06 Å for 16 nm thick BaTiO 3 .…”

“…The lattice parameters were a = 3.96 Å and c = 4.06 Å for 16 nm thick BaTiO 3 . Both in [115] and [116], the comparison of the x-ray diffraction θ /2 θ scans clearly showed the impact of the buffer insertion on the BaTiO 3 crystalline orientation. In the work of Ponath et al [116], STEM-HAADF images revealed that Ti atomic columns close to the top of the BaTiO 3 film are shifted downward from the cell center, meaning a ‘down’ polarization, which is in good agreement with their DFT calculations.…”

Nanocrystalline Ferroelectric BiFeO3 Thin Films by Low-Temperature Atomic Layer Deposition

“…[21][22][23] The unique characteristics of conformality, atomic scale control and low temperature deposition that atomic layer deposition technique (ALD) offers can have direct technological applications: well controlled interfaces, smaller and more demanding structures (3D substrates), increased density of devices, including those that require flexible and transparent substrates, that have been hindered by the high temperature thermal treatment constraints. 17,[24][25][26][27] This cost-effective chemical deposition technique is based on a self-limiting surface reaction mechanism that makes it very attractive for areaselective deposition. In principle, this could allow simultaneous patterning for the growing films, which offers some advantages for hard-to-pattern materials relative to traditional top-down patterning techniques.…”

“…This adds complexity in the materials processing in device integration. 2,[9][10][11][12][13][14][15][16][17] One approach is to achieve locally high temperatures using laser annealing. 18-20 Alternatively, efforts have been made to develop new low-temperature synthesis routes for ferroelectric perovskite oxides; many of these are based on solution methodologies requiring processing temperatures of 300ºC-400ºC.…”

Surface-hydrogen-induced metallization and rumpling in thin BaTiO3 films

“…4 As BTO is ferroelectric, its integration with Si or Ge adds additional versatility in the construction of a ferroelectric FET, [5][6][7] in microwave device applications, 8 or as a nonlinear optical material for Si nano-photonic devices. 9 Due to this interest in utilizing ferroelectricity of BTO, it is crucial that the polarization of BTO is kept intact during growth and processing, and so the understanding of the effects of defects on the polarization is essential.…”