Saturday, April 25, 2015

Chinese and US researchers dope & un-dope graphene FETs by ALD

Despite the tremendous world wide focus on the wonder material graphene, its pristine form can't be used in field-effect transistors (FETs) to replace current channel materials (Si, SiGe, III/V) between the source and drain suffer from the absence of a bandgap.

Here reseraches are seeking  to chemically modify or dope grapheneto open up a  band gap in the material. However, the carbon atoms in graphene are arranged in a two-dimensional sp2 hybridization surface, which makes it almost impossible to induce any chemical modification or doping without alteration of its idealized properties.

Finally, in order to form a super fast CMOS logic based on ultra fast graphene FETs (GFET) you need to be able to dope the GFETs in to NMOS and PMOS transistores and it has been proven very difficult to produce a stable n-type graphene transistors than its p-type counterpart.

A team of Chinese and US researchers [1, 2, 3, 4] have developed a simple method to produce n-type doping of graphene by using an ALD chamber. That is not all - the mechanism is reversible, meaning they can bring back graphene to p-type by a thermal anneal step. The main mechanism of n-type doping is driven by a surface charge transfer at graphene/redox interfaces during the ALD processing of Al2O3. Fantastic - Check out the details in the publication below!

Reversible n-Type Doping of Graphene by H2O-Based Atomic-Layer Deposition and Its Doping Mechanism
Li Zheng, Xinhong Cheng, Zhongjian Wang, Chao Xia, Duo Cao, Lingyan Shen, Qian Wang, Yuehui Yu, and Dashen Shen
J. Phys. Chem. C, 2015, 119 (11), pp 5995–6000
DOI: 10.1021/jp511562t

The pre-H2O treatment and Al2O3 film growth under a two-temperature-regime mode in an oxygen-deficient atomic layer deposition (ALD) chamber can induce n-type doping of graphene, with the enhancement of electron mobility and no defect introduction to graphene. The main mechanism of n-type doping is surface charge transfer at graphene/redox interfaces during the ALD procedure. More interestingly, this n-type doping of graphene is reversible and can be recovered by thermal annealing, similar to hydrogenated graphene (graphane). This technique utilizing pre-H2O treatment and an encapsulated layer of Al2O3 achieved in an oxygen-deficient ALD chamber provides a simple and novel route to fabricate n-type doping of graphene. (From grapfical abstract J. Phys. Chem. C, 2015, 119 (11), pp 5995–6000)

[1] State Key Laboratory of Functional Materials for Informatics
[2] Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
[3] University of Chinese Academy of Sciences, Beijing 100049, China
[4] University of Alabama in Huntsville, Huntsville, Alabama 35899, United States