Lithuanian Journal of Physics article / Lietuvos fizikos žurnalo straipsnis

LONG-TIME DRIFT INDUCED CHANGES IN ELECTRICAL CHARACTERISTICS OF GRAPHENE–METAL CONTACTS
Andrius Sakavičius, Vladimir Agafonov, Virginijus Bukauskas, Tomas Daugalas, Mindaugas Kamarauskas, Algimantas Lukša, Viktorija Nargelienė, Gediminas Niaura, Marius Treideris, and Arūnas Šetkus
State Research Institute Center for Physical Sciences and Technology, Savanorių 231, 02300 Vilnius, Lithuania
Email: andrius.sakavicius@ftmc.lt

Received 3 May 2020; revised 3 July 2020; accepted 1 September 2020

Chemical vapour deposition (CVD) graphene is commonly recognized as promising 2D material for development of electronic devices. However, the long-term drift of electrical parameters still requires deeper understanding before the technological means can be selected for an individual type of the devices. In this work, the changes in the electrical resistance were investigated over long time in the planar samples based on the CVD graphene with Au and Ni contacts. The samples were arranged as arrays of the resistors on a silicon substrate covered with a 250 nm layer of thermally grown silicon dioxide. The annealing in pure argon gas flow at 573 K was used to return the electrical properties of samples to the initial state. The effects of drift and annealing were compared for the three parts of structures, namely the electrical contact, the graphene sheet and the edge of the metal film with a hanging graphene sheet. For these parts, the resistance changes were related to the strain and doping of supported and hanged parts of the graphene sheet. Raman spectroscopy and Kelvin force probe microscopy were used to characterize charge doping, strain and work function in the graphene. The drift was explained in terms of the most prominent changes in the doping, strain and work function detected within the edge zone of the contact. It was proved that the annealing significantly changed the p-type doping and work function in the graphene layer in this edge zone. The properties were almost independent of test conditions in the SiO₂ supported graphene. The changes in the contact parameters produced by drift mechanisms were proved being reversible under proper annealing conditions.

Keywords: long-time drift, graphene, graphene–metal contacts, Raman spectroscopy, scanning probe microscopy, strain and doping in CVD graphene
PACS: 72.80.Vp, 68.65.Pq

GRAFENO IR METALO KONTAKTŲ ELEKTRINIŲ CHARAKTERISTIKŲ KITIMAS DĖL ILGALAIKIO DREIFO
Andrius Sakavičius, Vladimir Agafonov, Virginijus Bukauskas, Tomas Daugalas, Mindaugas Kamarauskas, Algimantas Lukša, Viktorija Nargelienė, Gediminas Niaura, Marius Treideris, Arūnas Šetkus

Fizinių ir technologijos mokslų centras, Vilnius, Lietuva

Darbe pristatomas tyrimas, kuriame buvo analizuotos CVD (cheminio garų nusodinimo) grafeno pagrindu pagamintų Au ir Ni CTLM (apskritiminės perdavimo linijos metodo) varžinių darinių elektrinių charakteristikų ilgalaikio stabilumo priežastys. Kontaktų iškaitinimas buvo naudojamas elektrines varžas atstatant į pradines vertes, būdingas tik ką pagamintiems grafeno bandiniams. Iškaitinimas buvo atliekamas Ar sraute, 573 K temperatūroje. Dėl parametrų kitimo bėgant laikui pasikeitusi grafeno bandinių elektrinė varža, kontaktinės ir sluoksnio varžos buvo atstatytos į pradines vertes.
Ramano spektroskopija buvo tirtas grafeno, esančio ant bandinių paviršiaus, legiravimo ir įtempimų kitimas bėgant laikui ir atstatymo metu. Analizuotos trys grafeno CTLM bandinių sritys: grafenas, esantis ant metalinių kontaktų, grafenas, esantis ant kontaktinio laiptelio srities, ir grafenas, esantis ant SiO₂ padėklo. Nustatyta, kad dėl bandinių kitimo bėgant laikui ir atstatymo didžiausi legiravimo kitimai įvyko grafeno sluoksnyje, esančiame ant kontaktinio laiptelio srities, o didžiausi įtempimų pokyčiai – grafeno sluoksnyje, esančiame ant metalinių kontaktų.
Kelvino jėgos spektroskopijos mikroskopija išmatuotos grafeno išlaisvinimo darbo vertės prieš CTLM bandinių iškaitinimą ir po. Nustatyta, kad išlaisvinimo darbo vertė sumažėjo grafeno sluoksnyje, esančiame ant Au kontaktų; po iškaitinimo ji padidėjo grafeno sluoksnyje, esančiame ant Ni kontaktų, ir W_Gr sumažėjo grafeno sluoksnyje, esančiame ant kontaktinio laiptelio srities bei SiO₂ padėklo. Išlaisvinimo darbo pokytis grafeno sluoksnyje, esančiame ant metalinių kontaktų, buvo didžiausias Au CTLM bandiniams, o W_Gr pokytis grafeno sluoksnyje, esančiame ant kontaktinio laiptelio srities, – Ni CTLM bandiniams.

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