Photo-responsivity of majority carrier graphene–insulator–silicon (GIS) photodetectors, which act as photocurrent amplifiers and thus have high potential for various future electro-optic applications requiring their high responsivity, low dark current, high on–off ratio and high detectivity.

A photocurrent amplifier operable at low bias voltages with high responsivity and detectivity is highly demanding for various optoelectronic applications. This study shows majority carrier graphene-native oxide-silicon (GOS) photocurrent amplifiers complying with the demands. The photocurrent amplification is primarily attributed to the photoinduced Schottky barrier height (SBH) lowering for majority carriers. The unavoidably formed thin native oxide layer between graphene and silicon during the wet graphene transfer process plays significant roles in lowering of the dark leakage current as well as photoinduced SBH lowering. As a result, the photocurrent to dark current ratio is as high as ∼12.7 at the optical power density of 1.45 mW cm–2. These GOS devices show a high responsivity of 5.5 AW–1 at an optical power (458 nm in wavelength) of 15 μWcm–2, which corresponds to ∼1400% quantum efficiency. Further the response speed is as fast as a few ten-microseconds. Thus, these GOS majority carrier photodiodes show the highest detectivity (2.35 × 1010 cm Hz1/2 W1–) among previously reported graphene-silicon photodiodes. However, the responsivity decreases with the optical power density due to the increasing recombination rate through the interface states proportional to the optical power density.

devices, the hurdle should be overcome by identifying the origin. However, the origin of the wide-range ideality factor was not yet been fully elucidated.The ideality factor is a measure of how efficiently an applied bias is delivered to the junction of the device. The ideality factor of GS devices can be influenced by both voltage-independent serial resistance and voltage-dependent attributes such as interface state and quantum capacitance. Thus, one can expect that the ideality factor changes with applied bias voltage.First of all, when a bias voltage is applied to a GS junction, the Fermi level of 2D graphene changes significantly in contrast to typical metal-oxide-semiconductor (MOS) devices due to the far less density of states of graphene compared to that of 3D metal. As a result, the effective Schottky barrier height and the resistance of graphene change with bias voltage. This directly influences the GS device performance and the ideality factor.Second, a peculiar issue related to the GS devices is the un avoidable wet graphene transfer process on a cleaned silicon wafer. During this process, oxidation of silicon occurs naturally. As a result, the GS devices inevitably have a native interfacial oxide layer between graphene and silicon although it may be very thin. This interfacial oxide layer directly influences the performance of GS devices. Although the layer can act as a tunneling barrier, which may enhance the effective potential barrier height, this effect has often been ignored because the layer is thin enough to assume that the transport property is largely governed by the semiconductor rather than limited by the tunneling.Third, the truncated silicon surface has high density of surface states. The surface states can exist as interface states of GS devices. The interface states can be equilibrated with silicon itself or with the graphene and this depends on the thickness of the interfacial oxide layer. Due to the very thin native oxide layer, one can expect that the silicon interface state can be mostly equilibrated with graphene rather than silicon itself. But this has not been confirmed yet.In this study, first we extract the voltage-dependent ideality factors of graphene-silicon Schottky diodes from their I-V characteristics based on Schottky emission theory. [13][14][15] We then compare the ideality factors with those obtained from the impedance spectra. [16,17] We designed an equivalent circuit model for analysis of impedance spectra accounting for Undoubtedly graphene-silicon (GS) heterostructure devices will play significant roles as future rectifiers, potential barrier modulators, photodetectors, photovoltaic devices, biochemical sensors, and so on. However, typical GS devices suffer from unusually wide-range voltage-dependent high ideality factors (η = 1.1-33.5). To overcome this hurdle, the origin of this wide-range voltage-dependent ideality factor should first be identified but this has not yet been fully studied. This study focuses on identifying the origin using impedance spectroscop...

Mapped photo-responsivity of a graphene–insulator–silicon photodetector having a double-electrode configuration illuminated with 10 μW of optical power and at an applied reverse bias voltage of −5 V.

A series of novel, soluble polyazomethines bearing fluorene and carbazole moieties in the main chain and solubility‐improving moieties in the side group (dibutyl, ethylhexyl, thienylethyloxy, furyl, and fluorenyl) were synthesized. Good‐quality films of these polymers were prepared through the conventional solution‐casting and drying processes. Depending on the polymer structure, some polymers showed a glass‐transition temperature (107–167 °C) and others showed a melting temperature (285–341 °C). The temperature of 5% weight loss under nitrogen atmosphere of the polymers ranged from 370 to 464 °C. The results indicated that the side groups incorporated into the polyazomethine structure in this work improved the polymer solubility without sacrificing thermal stability. Depending on the polymer structure, some of the polymers were crystalline whereas others were amorphous. All the polyazomethines were solution‐processable and thermally stable, making them potential candidate materials for applications in microelectronics and aerospace. Moreover, the features in the UV–visible spectra of the polyazomethines were redshifted as compared with those of the monomers from which the polymers were synthesized, indicating that these polymers, if combined with an appropriate doping agent to improve the light‐emitting and conducting abilities, may be good candidate materials for optoelectronic devices. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 825–834, 2004