Oxide-Confined Formation of Germanium Nanowire Heterostructures for High-Performance Transistors

Abstract

Over the past several years, the formation of nanowire heterostructures via a solid-state reaction between a semiconductor nanowire and metal contact pads has attracted great interest. This is owing to its ready application in nanowire field-effect transistors (FETs) with a well-controlled channel length using a facile rapid thermal annealing process. We report the effect of oxide confinement on the formation of Ge nanowire heterostructures via a controlled reaction between a vapor-liquid-solid-grown, single-crystalline Ge nanowire and Ni pads. In contrast to the previous formation of Ni(2)Ge/Ge/Ni(2)Ge nanowire heterostructures, a segment of high-quality epitaxial NiGe was formed between Ni(2)Ge and Ge with the confinement of Al(2)O(3) during annealing. Significantly, back-gate FETs based on this Ni(2)Ge/NiGe/Ge/NiGe/Ni(2)Ge heterostructure demonstrated a high-performance p-type transistor behavior, showing a large on/off ratio of more than 10(5) and a high normalized transconductance of 2.4 μS/μm. The field-effect hole mobility was extracted to be 210 cm(2)/(V s). Temperature-dependent I-V measurements further confirmed that NiGe has an ideal ohmic contact to p-type Ge with a small Schottky barrier height of 0.11 eV. Moreover, the hysteresis during gate bias sweeping was significantly reduced after Al(2)O(3) passivation, and our Ω-gate Ge nanowire FETs using Al(2)O(3) as the top-gate dielectric showed an enhanced subthreshold swing and transconductance. Therefore, we conclude that the Al(2)O(3) layer can effectively passivate the Ge surface and also serve as a good gate dielectric in Ge top-gate FETs. Our innovative approach provides another freedom to control the growth of nanowire heterostructure and to further achieve high-performance nanowire transistors.

Ge nanowire transistors with high-quality interfaces by atomic-scale thermal annealing

“…3). As a result of the Al203 confinement, a segment of high-quality epitaxial NiGe was formed between Ni2Ge and Ge [4]. The formed NiGe has an orthorhombic crystal structure (space group 62) with the set of lattice constants: a = 0.538 nm, b = 0.342 nm, and c = 0.581 run.…”

“…3(c)). The subthreshold swing SS=1.74 V/dec is relatively large due to the use of a thick 300 nm Si02 back-gate dielectric, and it can be further reduced with a top-gate geometry [4]. Besides to the confmement effect during the germanide growth, it was also found that Ah03 could effectively passivate the Ge nanowire surface as evident from the dramatically improvement in the transistor performance after the ALD-AI203 capping and the significant suppression of the hysteresis during gate bias sweeping.…”

“…I N the effort of making high-quality nanoscale source/drain contacts to a semiconductor nanowire channel, one attractive strategy is to use thermal annealing to promote the solid-state reaction of metal contacts with semiconductor nanowires [1][2][3][4][5][6]. In the metal-Si(Ge) nanowire system, the produced silicide(germanide) region after annealing can be used as Schottky source/drain contacts for the fabrication of Si(Ge) nanowire transistors.…”

Ultrahigh-gain single SnO2 nanowire photodetectors made with ferromagnetic nickel electrodes

“…4,5 In fact, a variety of optoelectronic devices based on one-dimensional nanowires (NWs) have been developed, such as emitters, 6,7 detectors 8,9 and transistors. 10,11 Recently, tin dioxide (SnO 2 ) with a wide direct band gap of 3.6 eV and high quantum efficiency in the ultraviolet region has attracted a great deal of attention, and there are potential applications in many practical devices, such as visible-blind photodetectors and solar cells. [12][13][14][15] In addition, because NWs have a high surface-to-volume ratio, the surface of NWs can influence the conductivity markedly.…”

Growth kinetics controlled rational synthesis of germanium nanotowers in chemical vapor deposition

“…One-dimensional (1D) Ge nanowires show promising applications in high-performance field effect transistor [16][17][18] due to its high carrier mobility and large aspect ratio desirable for carrier transport. Three-dimensional (3D) tubular [19] or porous [20] Ge nanostructures are candidates as anode materials for high-capacity lithium-ion batteries as the porous structure can accommodate volume expansion in the charging and discharging cycling process of battery.…”