The optical and electrical properties of vertical graphene grown on diamond substrate

Vertical graphene (VG) is a promising carbon material for optoelectronics applications owing to its strong light absorption and abundant edge sites. Compared with silicon-based devices, directly integrating VG on diamond substrates enhances interfacial bonding and reduces phonon scattering, enabling superior stability and performance. However, the influence of plasma–substrate interactions under bias on the structural and functional evolution of VG has not been fully understood. In this work, VG was synthesized on diamond using a direct current bias-assisted plasma-enhanced chemical vapor deposition system under controlled negative bias voltages of 90 V, 120 V, and 150 V. The results show that moderate bias promotes vertical alignment, with nanoflakes reaching ~2.6 µm in height, exhibiting multilayer stacking and cauliflower-like morphology, while excessive bias causes disorder and plasma instability. Optical characterization reveals broadband absorption exceeding 85% from 400 to 2400 nm and electrical testing demonstrates a minimum sheet resistance of 48.6 Ω/☐ with conductivity up to 2060 S·cm−1. Kelvin probe force microscopy further shows work functions of ~5.00–5.08 eV, and confirms bias-dependent modulation of surface potential linked to defect-assisted Fermi-level tuning. These findings confirm that bias-assisted growth enables precise control over VG morphology and properties. The optimized DC plasma process provides a robust route to fabricate high-quality VG/diamond heterostructures, while the resulting all-carbon system exhibits excellent photoelectric performance, highlighting its potential for broadband optoelectronic applications.