Three-dimensional graphene (3D-Gr) with excellent light absorption properties has received enormous interest, but in conventional processes to prepare 3D-Gr, amorphous carbon layers are inevitably introduced as buffer layers that may degrade the performance of graphene-based devices. Herein, 3D-Gr is prepared on germanium (Ge) using two-dimensional graphene (2D-Gr) as the buffer layer. 2D-Gr as the buffer layer facilitates the in situ synthesis of 3D-Gr on Ge by plasma-enhanced chemical vapor deposition (PECVD) by promoting 2D-Gr nucleation and reducing the barrier height. The growth mechanism is investigated and described. The enhanced light absorption as confirmed by theoretical calculation and 3D-Gr/2D-Gr/Ge with a Schottky junction improves the performance of optoelectronic devices without requiring pre-and post-transfer processes. The photodetector constructed with 3D-Gr/2D-Gr/Ge shows an excellent responsivity of 1.7 A W −1 and detectivity 3.42 × 10 14 cm Hz 1/2 W −1 at a wavelength of 1550 nm. This novel hybrid structure that incorporates 3D-and 2D-Gr into Ge-based integrated circuits and photodetectors delivers excellent performance and has large commercial potential.

Surface-enhanced Raman scattering (SERS) substrates based on graphene and its derivatives have recently attracted attention among those interested in the detection of trace molecules; however, these substrates generally show poor uniformity, an unsatisfactory enhancement factor, and require a complex fabrication process. Herein, we design and fabricate threedimensional (3D) graphene/silicon (3D-Gr/Si) heterojunction SERS substrates to detect various types of molecules. Notably, the detection limit of 3D-Gr/Si can reach 10 −10 M for rhodamine 6G (R6G) and rhodamine B (RB), 10 −7 M for crystal violet (CRV), copper(II) phthalocyanine (CuPc), and methylene blue (MB), 10 −8 M for dopamine (DA), 10 −6 M for bovine serum albumin (BSA), and 10 −5 M for melamine (Mel), which is superior to most reported graphene-based SERS substrates. Besides, the proposed 3D-Gr/Si heterojunction SERS substrates can achieve a high uniformity with relative standard deviations (RSDs) of less than 5%. Moreover, the 3D-Gr/Si SERS substrates are reusable after washing with ethyl alcohol to remove the adsorbed molecules. These excellent SERS performances are attributed to the novel 3D structure and abundantly exposed atomically thin edges, which facilitate charge transfer between 3D-Gr and probe molecules. We believe that the 3D-Gr/Si heterojunction SERS substrates offer potential for practical applications in biochemical molecule detection and provide insight into the design of high-performance SERS substrates.

Two-dimensional graphene films and graphene derivatives have attracted broad interest because of the large potential in optoelectronic applications. However, improving the performance of photodetectors based on graphene films and graphene derivatives remains a great challenge. Through replacing graphene films with vertically oriented graphene (VOG), which is subsequently functionalized with graphene quantum dots (GQDs), a functional VOG is assembled on the germanium (Ge) heterojunction (designated as GQDs/VOG/Ge) for near-infrared light detection. The properties of the photodetector are enhanced by the synergistic effects of GQDs and VOG with regard to light absorption and electron transport. Functional modification of VOG is an efficient way to adjust and control the Fermi level of VOG, increase the built-in potential of the Schottky junctions, and facilitate separation of photoinduced electron and hole pairs. The as-fabricated photodetector shows excellent responsivity (1.06 × 10 6 AW −1 ) and detectivity (2.11 × 10 14 cm Hz 1/2 W −1 ) at a wavelength of 1550 nm. Investigation of the photoresponse reveals response rates with microsecond rise/fall time in addition to excellent reproducibility and long-term stability. The results reveal a simple strategy to fabricate novel structures for high-performance graphene-based photodetectors.

The photodetector exhibits outstanding performance at 1550 nm with high detectivity and photoresponsivity and a microsecond-level light response which is attributed to the synergistic effects of FAPbI3 QDs and VAGAs.

No abstract