Performance evaluation of GaN light-emitting diodes using transferred graphene as current spreading layer

Abstract

This study elucidates the correlation among conductivity of graphene and interface aspects in GaN light-emitting diodes (LEDs). Using a multilayer graphene of low sheet resistance, it is demonstrated that graphene alone can make ohmic contact with p-GaN without necessitating additional interlayer. Large-area blue LED with relatively low contact resistance in the order of 10−2 ohm-cm2 and improved forward voltage of 3.2 ± 0.1 V was realized irrespective of the use of the interlayer. The results from parallel evaluation experiments performed by varying the layer numbers of graphene with ultrathin NiOx interlayer revealed that the poor lateral conductivity of monolayer or few layer graphene can be well compensated by the interlayer. A combination of three layer graphene and NiOx offered device with enhanced electro-optical performance. But the Schottky barrier associated with the inadequate adhesion of transferred graphene dominates all the benefits and becomes a major bottleneck preventing the formation of low resistance stable ohmic contact.

Enhanced opto-electrical properties of graphene electrode InGaN/GaN LEDs with a NiOx inter-layer

“…For GaN-based LED device, the p-type GaN layers own relatively high resistivity resulting in the inhomogeneous distribution of current density [1]. Obviously, transparent current spreading layers (TCSLs) are crucial for the homogeneous hole injection into the active regions of the LEDs.…”

“…Several pioneering works have reported the application of graphene film as TCSLs in GaN-based LEDs [1,2,[5][6][7]. However, it is still difficult to form good ohmic contact between graphene and p-GaN due to the mismatch of work function, which causes high operating voltage and great power loss.…”

Fundamentals of Chemical Vapor Deposited Graphene and Emerging Applications

“…GaN is one of the most promising wide bandgap semiconductors for applications in optoelectronic and other electronic devices such as light-emitting diodes, laser diodes, solar cells, and high-electron-mobility transistors [95][96][97][98][99]. The transparency of metal oxide conductors is poor in the UV and near UV region, which affects the photodetectors efficiency and brightness of LEDs.…”

Carbon nanotube-graphene composite film as transparent conductive electrode for GaN-based light-emitting diodes

“…9,10 Recently, graphene has been proposed and demonstrated as TCE on GaN-based LED. However, due to large work function (Φ) discrepancy with p-GaN 11 , high forward voltage 12 and poor current spreading 13 , the performance of the LED with graphene TCE is still not at par with ITO-based TCE. Hence, in order to improve the performance of the graphene-based TCE on GaN-based LED, many groups have suggested a more exquisite solid-phase layer-stacking, hybridizing graphene-based TCE with ITO rods 14 , thin ITO layer 15,16 , metal nanowires (i.e.…”

“…20,30 Apart from that, unfavourable conductivity and charge scattering across grain boundaries of polycrystalline graphene film also affected the lateral current spreading performance of bare graphene TCE. 12 On the other hand, when CNT-graphene composite film was adopted as TCE, the Vf was reduced down to 6.12 V at 20 mA. This is largely due to improved interconnected network and reduced contact resistivity of network CNT-graphene composite film.…”