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

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.

Strain engineering in graphene by laser irradiation

“…On the other hand, laser irradiation of graphene on silicon oxide leads to a horizontal shift, consistent with an increase in hole doping as well as in compressive strain, in agreement with recent experiments performed by laser pulses. 9,10 This interpretation is also supported by the behaviour of the linewidth of the G peak, presented in Fig. 3(b), where a substrate-dependent response was observed.…”

“…5,6 One of the most attractive characteristics of graphene is the ability to control its electronic and optical properties through the charge carrier density. This can be achieved by chemical, 7 electronic, 1 optical, [8][9][10] or mechanical 11 means. Moreover, it has been suggested that the electronic and optical properties of graphene depend strongly on its strain distribution.…”

“…14,15 It has been demonstrated that laser irradiation even at low powers can lead to both reversible 8 and irreversible changes in graphene. 9,10 Typically, such changes are related either to charge carrier doping originating from the presence of charge traps in the substrate as in the latter case or they arise from hydrophilic/hydrophobic properties of the substrate as in the former case. Here, we study the effects of laser illumination on graphene deposited on lithium niobate and silicon oxide substrates.…”

Bright visible light emission from graphene

“…However, the thermal radiation from electrically biased graphene supported on a substrate 8,9,[15][16][17] has been found to be limited to the infrared range and 3 to be inefficient as an extremely small fraction of the applied energy (~ 10 -6 ) 8,9 is converted into light radiation. Such limitations are the direct result of heat dissipation through the underlying substrate 18 and significant hot electron relaxation from dominant extrinsic scattering effects such as charged impurities 19 and surface polar optical phonon interaction 20 , limiting the maximum operating temperatures.On the other hand, a freely suspended graphene is mostly immune to such undesirable vertical heat dissipation 10 and extrinsic scattering effects 21,22 , promising much more efficient and brighter radiation in the infrared-to-visible range. Fortuitously, due to the strong Umklapp phonon-phonon scattering 23 , we find that the thermal conductivity of graphene at high lattice temperatures (1800 ± 300 K) is greatly reduced (~ 65 Wm -1 K -1 ), which additionally suppresses lateral heat dissipation; therefore, hot electrons (~ 2800 K) become spatially localised at the centre of the suspended graphene under modest electric fields (~ 0.4 V/µm), greatly increasing the efficiency and brightness of the light emission.…”

Multi- and few-layer graphene on insulating substrate via pulsed laser deposition technique

“…It possesses exceptional thermal, electrical, optical and mechanical properties leading to its potential applications in research and industry as transparent electrodes, field emitters, biosensors, etc. [1][2][3][4][5][6][7][8]. Graphene has been prepared by several techniques viz.…”