Chemically modified multilayer graphene with metal interlayer as an efficient current spreading electrode for InGaN/GaN blue light-emitting diodes

Abstract

This paper describes a detailed systematic study based on the fabrication and performance of InGaN/GaN blue light-emitting diodes (LEDs) with multilayer graphene film as a current spreading electrode. Two facile approaches to improve the electrical coupling between graphene and p-GaN layer are demonstrated. Using chemical charge transfer doping, the work function (Φ) of graphene is tuned over a wide range from 4.21 to 4.93 eV with substantial improvements in sheet resistance (R s). Compared with pristine graphene, the chemically modified graphene on p-GaN yields several appealing characteristics such as low specific contact resistance (ρc) and minimized barrier height. In addition, insertion of a thin gold interlayer between graphene and p-GaN profoundly enhances the contact properties at the interface. Combining these two approaches in a single LED, the current spreading and thus the device forward voltage (V f) are considerably improved comparable to that of an LED fabricated with an indium tin oxide electrode. The importance of pre-metal deposition oxygen plasma treatment and rapid thermal annealing in improving the contact characteristics is also addressed.

Enhanced performance of GaN-based light-emitting diodes with graphene/Ag nanowires hybrid films

“…The values of ρ c for graphene/AgNWs/p-GaN before and after annealing are 1.34 × 10 −1 · cm and 1.05 × 10 −1 · cm, respectively. Similar results were observed in other two concentrations of hybrid films (0.1 and 1.0 mg/mL) and the values obtained are consistent with the values reported by Wang, et al 21 and S Chandramohan, et al 15 The improvement of graphene/AgNWs/p-GaN contacts, can be attributed to the improved adhesive and a better electrical coupling between hybrid films and p-GaN due to the annealing. It can be also attributed to the formation of Ag-Ga solid solution, which is formed during the thermal annealing at elevated temperature.…”

“…4(a)-4(d) show the optical images of light emission of different LED devices at 1 mA. The light emission of graphene-only LEDs was around the p-type metal pad due to the strong current crowding, 15 as shown in Fig. 4(a).…”

“…12,13 In addition, the sheet resistance of monolayer graphene (∼2 k /sq due to the presence of different defects) 14 is much higher than that of currently used transparent electrodes, resulting in the limited current spreading effect. Furthermore, the difference in work function between graphene (∼4.8 eV) and p-GaN (∼7.5 eV) 15 generates a high Schottky barrier height (SBH), which leads to the inferior electrical contact properties and high forward voltage. Recently, many groups have proposed different effective approaches to overcome these problems, like using chemical charge transfer doping to tune the work function of graphene, 15 inserting the metal interlayer 16 between graphene and p-GaN, or introducing metal nanoparticles 17 onto graphene.…”

“…Furthermore, the difference in work function between graphene (∼4.8 eV) and p-GaN (∼7.5 eV) 15 generates a high Schottky barrier height (SBH), which leads to the inferior electrical contact properties and high forward voltage. Recently, many groups have proposed different effective approaches to overcome these problems, like using chemical charge transfer doping to tune the work function of graphene, 15 inserting the metal interlayer 16 between graphene and p-GaN, or introducing metal nanoparticles 17 onto graphene. With these methods, the contact properties between graphene and a Emails: lzq@semi.ac.cn; hongweizhu@tsinghua.edu.cn p-GaN and the electrical performances of LED devices have been greatly improved.…”

Improved electrode performance in gallium nitride LEDs

“…By introducing a thin gold layer between the MLG and p-GaN followed by rapid thermal annealing, the ¡ c was further reduced to 0.24 -cm 2 . 9 We fabricated InGaN/GaN multi-quantum-well LEDs with both ITO electrodes and MLG (pristine and doped graphene both with and without a gold interlayer). Figure 2 compares the I-V characteristics of the devices.…”