Abstract
Germanane, a hydrogen-terminated graphane analogue of germanium has generated interest as a potential 2D electronic material. However, the incorporation and retention of extrinsic dopant atoms in the lattice, to tune the electronic properties, remains a significant challenge. Here, we show that the group-13 element Ga and the group-15 element As, can be successfully doped into a precursor CaGe2 phase, and remain intact in the lattice after the topotactic deintercalation, using HCl, to form GeH. After deintercalation, a maximum of 1.1% As and 2.3% Ga can be substituted into the germanium lattice. Electronic transport properties of single flakes show that incorporation of dopants leads to a reduction of resistance of more than three orders of magnitude in H2O-containing atmosphere after As doping. After doping with Ga, the reduction is more than six orders of magnitude, but with significant hysteretic behavior, indicative of water-activation of dopants on the surface. Only Ga-doped germanane remains activated under vacuum, and also exhibits minimal hysteretic behavior while the sheet resistance is reduced by more than four orders of magnitude. These Ga- and As-doped germanane materials start to oxidize after one to four days in ambient atmosphere. Overall, this work demonstrates that extrinsic doping with Ga is a viable pathway towards accessing stable electronic behavior in graphane analogues of germanium.
Highlights
Having previously grown phosphorus-doped GeH (P:GeH) [29] using this method, here, we explored whether other group-13 and group-15 elements (Al, Ga, As and Sb) can be included as dopants onto the germanane framework, and how these dopants affect the stability and electronic properties of GeH
Using X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS) we show that up to 1.1% and 2.3% of As and Ga, respectively, can be substituted onto the germanane lattice
We have demonstrated that gallium and arsenic can be incorporated into a precursor CaGe2 Zintl phase and are retained in the 2D germanium framework after the topotactic deinterca
Summary
Since the discovery of graphene [1], the quest to discover and measure novel two dimensional and layered materials has led to the investigation of group-14 and group-15 allotropes of graphene and graphane [1,2,3,4,5,6,7,8,9,10,11,12,13,14], transition-metal dichalcogenides [15,16,17,18,19], and layered van der Waals materials [20,21,22]. The incorporation of more dopant produced lower sheet resistances in H2O-containing ambient atmosphere, while only the gallium-doped samples continue to show dopant activation under vacuum and H2O-free conditions. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) provided further verification of the incorporation of dopant atoms into GeH.
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