Towards substrate engineering of graphene–silicon Schottky diode photodetectors

Abstract

Graphene-Silicon Schottky diode photodetectors possess beneficial properties such as high responsivities and detectivities, broad spectral wavelength operation and high operating speeds. Various routes and architectures have been employed in the past to fabricate devices. Devices are commonly based on the removal of the silicon-oxide layer on the surface of silicon by wet-etching before deposition of graphene on top of silicon to form the graphene-silicon Schottky junction. In this work, we systematically investigate the influence of the interfacial oxide layer, the fabrication technique employed and the silicon substrate on the light detection capabilities of graphene-silicon Schottky diode photodetectors. The properties of devices are investigated over a broad wavelength range from near-UV to short-/mid-infrared radiation, radiation intensities covering over five orders of magnitude as well as the suitability of devices for high speed operation. Results show that the interfacial layer, depending on the required application, is in fact beneficial to enhance the photodetection properties of such devices. Further, we demonstrate the influence of the silicon substrate on the spectral response and operating speed. Fabricated devices operate over a broad spectral wavelength range from the near-UV to the short-/mid-infrared (thermal) wavelength regime, exhibit high photovoltage responses approaching 10 6 V/W and short rise-and fall-times of tens of nanoseconds.Graphene is an appealing material for ultrafast and broadband photodetection applications due to its high charge carrier mobility [1, 2] and ultra-wide spectral absorption range [3,4]. The initial examples of graphene photodetectors are mostly based on metal-graphene (MG) junctions [5][6][7] and graphene p-n junction architectures [8][9][10]. Despite their broadband operation at ultrafast speeds [11], they generally exhibit low responsivities (limited to a few mAW −1 ) due to the intrinsically low optical absorption of monolayer graphene (2.3%) [12]. Further, the small photoactive area limits their use for realworld applications [9,10,13]. Recently, there is a surge of interest in using graphene to replace the metal electrode on semiconductor surfaces to realize Schottky diodes [17]. A further benefit of the graphene-silicon Schottky platform is its simple architecture, suitability for large scale fabrication and the potential for integration into the back end-of-line (BEOL) CMOS processing [11,55]. Particularly in photodetection applications, the G-Si diode provides an efficient hybrid platform where both graphene and silicon can be used as absorbing materials for different wavelength ranges [36]. Devices shows high responsivities comparable to commercial silicon photodiodes for wavelength ranges with photon energies above the silicon bandgap which is enabled by the high optical transmittance of graphene of more than 97% [27,36]. Detection of radiation with energies below the silicon band gap is enabled by the broadband absorption of graphene [25,26]. Respon...

Bilayer graphene/HgCdTe based very long infrared photodetector with superior external quantum efficiency, responsivity, and detectivity

“…3c shows the J light , J light /J dark ratio, and LDR for various P in values at zero-bias and 77 K. The device exhibits J light /J dark ratio of 4.8 Â 10 14 and LDR of 293.55 dB at 2 W cm À2 in self-powered mode and are better than that of Gr-Si based heterojunction photodetector. 84,85 The photocurrent density J light and incident power P in satisfy the relationship 86…”

High Responsivity and Quantum Efficiency of Graphene/Silicon Photodiodes Achieved by Interdigitating Schottky and Gated Regions

“…Another approach is to utilize interfacial oxide layers on photodiodes. Selvi et al demonstrated that such interfacial oxides increase the Schottky barrier height (SBH) and lead to an enhancement in photovoltage responsivity, particularly for low light intensities 31 . Complex nanotip patterning of substrates was employed to improve the photoresponse of G/Si Schottky diodes 28 .…”

Visible and infrared photocurrent enhancement in a graphene-silicon Schottky photodetector through surface-states and electric field engineering

“…Diffraction limited spot sizes were ≈ 1µm and 2µm, respectively, and SPM measurements were carried out at an applied reverse bias voltage of V b = -2V. The laser light was chopped at a frequency f = 2kHz and the electrical signals recorded using a lock-in amplifier (Zurich Instruments HF2LI/HF2TA) [7]. Employed lock-in technique allows characterization of the photocurrent-magnitude and -phase to determine the absolute photoresponse as well as inferring time delays between optical excitation and electrical response of the devices.…”

“…This inhomogeneity can be attributed to the non-uniform interface and quality of the GSi Schottky junction. Previous studies highlighted the importance and implications of the natural oxide layer formed between graphene and silicon [20,21] and the re-growth of this oxide layer after device fabriation [7]. The interfacial oxide layer thickness and quality influence the Schottky barrier height and with it the efficiency of conversion of infrared light into electrical current.…”