Direct growth of graphene on GaN via plasma-enhanced chemical vapor deposition under N₂ atmosphere

Abstract

One of the bottlenecks in the implementation of graphene as a transparent electrode in modern opto-electronic devices is the need for complicated and damaging transfer processes of high-quality graphene sheets onto the desired target substrates. Here, we study the direct, plasma-enhanced chemical vapor deposition (PECVD) growth of graphene on GaN-based light-emitting diodes (LEDs). By replacing the commonly used hydrogen (H2) process gas with nitrogen (N2), we were able to suppress GaN surface decomposition while simultaneously enabling graphene deposition at <800 °C in a single-step growth process. Optimizing the methane (CH4) flow and varying the growth time between 0.5 h and 8 h, the electro-optical properties of the graphene layers could be tuned to sheet resistances as low as ∼1 kΩ/□ with a maximum transparency loss of ∼12%. The resulting high-quality graphene electrodes show an enhanced current spreading effect and an increase of the emission area by a factor of ∼8 in operating LEDs.

Quantifying Mn Diffusion through Transferred versus Directly Grown Graphene Barriers

“…Translating these performance enhancements to functional substrates at the wafer scale will require directly grown graphene synthesis approaches on the substrate of interest. For example, CVD approaches using small molecules, activated precursors, or plasma-enhanced CVD processes − show promise for reducing the graphene synthesis temperature and may be a route for graphene growth directly on GaAs and other technologically important compound semiconductors.…”

Quantifying Mn diffusion through transferred versus directly-grown graphene barriers

“…Translating these performance enhancements to functional substrates at wafer scale will require direct graphene synthesis approaches on the substrate of interest. For example, CVD approaches using small molecules [23], activated precursors [24], or plasmaenhanced CVD processes [25][26][27] show promise for reducing the graphene synthesis temperature, and may be a route for graphene growth directly on GaAs and other technologically important compound semiconductors.…”

Graphene as a Transparent Conductive Electrode in GaN-Based LEDs

“…Graphene directly grown on the p-side of GaN-based LEDs is expected to solve problems originating from the transfer process, such as bad adhesion, polymer residuals, defects and other damage introduced during transfer. Three main methods for direct integration of graphene layers as TCSL into GaN-based LED are reported: spray deposition of a graphene dispersion solution with a subsequent heating treatment (chemically converted graphene, CCG) [ 50 , 63 ], catalyzed graphene growth with W/Ni using rapid thermal annealing (RTA) post processing [ 64 ] and plasma enhanced chemical vapor deposition (PECVD) with [ 65 , 66 ] and without catalysts [ 67 , 68 ].…”

“…However, the expected values of of ~10–100 Ω/sq and of ~mΩcm 2 have not been achieved through either of the above-mentioned methods. The possible reasons are the relatively small grain size of graphene (~30 nm) and the high defect density, with distances between defects of around 2–5 nm [ 68 ], as reported for directly grown graphene. The grain boundaries and defects are all scattering centers and contribute to the increase of sheet and contact resistance.…”

“…The right panel shows the current-voltage (I-V) characteristics and the light emission in a LED chip with graphene TCSL (red I-V curve and lower image) and without graphene TCSL (blue I-V curve and upper left image); ( b ) Optical images of light emission of a typical LED device (inset) and the I-V characteristics (plot) of a LED device with transferred graphene (i.e., TG, right inset, grey points in the I-V plot) and with directly grown graphene (i.e., DG, left inset, blue points in the plot). ( a ) Data from recent work and reproduced with permission from [ 68 ]. Copyright 2020 The Author(s).…”