Focused-Laser-Enabled p-n Junctions in Graphene Field-Effect Transistors

Young Duck Kim, Myung-Ho Bae, Jung-Tak Seo, Yong Seung Kim, Hakseong Kim, Jae Hong Lee, Joung Real Ahn, Sang Wook Lee, Seung-Hyun Chun and Yun Daniel Park “Focused-Laser-Enabled p-n Junctions in Graphene Field-Effect Transistors”, ACS Nano, DOI : 10.1021/nn402354j (2013)

지금까지의Graphene field-effect transistor에서 p-n junctions 형성 및 local doping effect를 위해서는 local electrode, chemical modification 등과 같이 추가적인 공정및 구조가 필요하였다. 본 연구에서는 graphene 에서 다양한 p-n junctions 형성을 추가적인 공정 및 구조 없이 442 nm 레이저만을 입사하여 다양한 p-n junctions 형성 및 the Dirac voltage의 이동을 조절 할 수 있음을 보였다. 레이저 입사에 따른 graphene의 local doping effect 및 p-n–p 와 p-n-p-n-p 접합 형성은 gate oxide에 존재하는 charge trap density를 레이저 에 의해 조절 가능하기 때문이다. 이러한 p-n junction 형성 및 local doping특성 및 공간적 분포를 gate-dependent scanning photocurrent microscopy 를 이용하여 확인하였으며 gate oxide 에 존재하는charge trap sites의 에너지 베리어가 약 2.6 eV 임을 확인하였다. 본 연구는 그래핀을 이용한 opto-electronic device에 대한 깊은 이해와 성능 향상을 의해 필수적이며 그래핀을 이용한optically trigged novoltaic memory device 및 high efficient energy harvesting device 실현에 큰 기여할 것으로 기대된다.

Abstract:
With its electrical carrier type as well as carrier densities highly sensitive to light, graphene is potentially an ideal candidate for many optoelectronic applications. Beyond the direct light-graphene interactions, indirect effects arising from induced charge traps underneath the photoactive graphene arising from light-substrate interactions must be better understood and harnessed. Here, we study the local doping effect in graphene using focused-laser irradiation, which governs the trapping and ejecting behavior of the charge trap sites in the gate oxide. The local doping effect in graphene is manifested by large Dirac voltage shifts and/or double Dirac peaks from the electrical measurements and a strong photocurrent response due to the formation of a p-n-p junction in gate-dependent scanning photocurrent microscopy. The technique of focused-laser irradiation on a graphene device suggests a new method to control the charge-carrier type and carrier concentration in graphene in a nonintrusive manner as well as elucidate strong light-substrate interactions in the ultimate performance of graphene devices.

ACS Nano, Article ASAP
DOI: 10.1021/nn402354j
Publication Date (Web): June 20, 2013
http://pubs.acs.org/doi/abs/10.1021/nn402354j