Search

The lack of a sizeable band gap has so far prevented graphene from building effective electronic and optoelectronic devices despite its numerous exceptional properties. Intensive theoretical research reveals that a band gap larger than 1 eV can only be achieved in sub-3 nm wide graphene nanoribbons (GNRs), but real fabrication of such ultranarrow GNRs still remains a critical challenge. Herein, we demonstrate an approach for the synthesis of ultranarrow and photoluminescent semiconducting GNRs by longitudinally unzipping single-walled carbon nanotubes. Atomic force microscopy reveals the unzipping process, and the resulting 2.2 nm wide GNRs are found to emit strong and sharp photoluminescence at ∼685 nm, demonstrating a very desirable semiconducting nature. This band gap of 1.8 eV is further confirmed by follow-up photoconductivity measurements, where a considerable photocurrent is generated, as the excitation wavelength becomes shorter than 700 nm. More importantly, our fabricated GNR field-effect transistors (FETs), by employing the hexagonal boron nitride-encapsulated heterostructure to achieve edge-bonded contacts, demonstrate a high current on/off ratio beyond 105 and carrier mobility of 840 cm2/V s, approaching the theoretical scattering limit in semiconducting GNRs at room temperature. Especially, highly aligned GNR bundles with lengths up to a millimeter are also achieved by prepatterning a template, and the fabricated GNR bundle FETs show a high on/off ratio reaching 105, well-defined saturation currents, and strong light-emitting properties. Therefore, GNRs produced by this method open a door for promising applications in graphene-based electronics and optoelectronics.

The graphene ballistic rectifier uses the ultra-high carrier mobility of graphene to rectify ballistic carriers in an asymmetric nanostructure, and has been previously shown to operate beyond 650 GHz. Unlike conventional diodes and transistors, it does not require a bandgap. Building on the previously developed extended Buttiker-Landauer formula for semiconductors, we derive an analytical theory suitable for coexistence of electrons and holes in semi-metal graphene. Four ballistic rectifier designs are fabricated and compared. The developed theory fits their characteristics well, with derived parameters showing good agreement with device geometries. We also predict achievable responsivities of at least 50,800 V/W and noise-equivalent powers of 0.51 pW/Hz1/2 using these designs, far better than has so far been achieved. Importantly, this theory predicts increased responsivities with a large difference in carrier mobilities. Using the theory presented here, other graphene based ballistic nanodevices may be designed and optimized.

Although graphene can operate in the ballistic transport regime at room temperature, there are very few devices harnessing this property. Here we present a novel device called the ballistic rectifier which circumvents the problem of opening a bandgap in graphene. Based on the device theory, we propose four different asymmetric planar structures. All devices are working and show responsivity higher than 1,000 V/W at room temperature, with noise-equivalent power as low as 4.16 pW/Hz$^{\mathbf {1/2}}$. These properties make GBRs a suitable candidate for THz detection.

Here we present theory and measurements for a bridge rectifier formed from arrays of graphene self-switching diodes (GSSDs). Graphene’s extremely high carrier mobility allows GSSDs to work at THz frequencies, with the bridge rectifier structure allowing for full wave rectification of an AC signal. We derive an equation for the voltage output of a GSSD bridge rectifier, predicting a quadratic dependence on input current. This relationship is confirmed using AC and DC measurements. The fabricated rectifier has a high room temperature intrinsic responsivity of 3,230 V/W at low frequency and a low noise equivalent power of 7.0 pW/Hz1/2. Moving forward, similar devices using CVD graphene have been tested and shown to function with high responsivity.

Here, we present theory and measurements for a bridge rectifier formed from arrays of graphene self-switching diodes (GSSDs). Despite graphene's lack of a bandgap and high carrier concentration causing a reduced rectification ratio, the extremely high carrier mobility will allow GSSDs to work at frequencies well into the THz region. Compared with a single SSD array, the bridge rectifier structure allows for full-wave rectification of an AC signal. Here we derive an equation for the voltage output of a bridge rectifier formed from GSSDs, which predicts a quadratic relationship between output voltage and input current. This relationship is confirmed using AC and DC measurements. The fabricated rectifier is found to have a high room temperature intrinsic responsivity of [Formula: see text] at low frequency and a low noise equivalent power of [Formula: see text].