Photo-FETs: phototransistors enabled by 2D and 0D nanomaterials

The large diversity of applications in our daily lives that rely on photodetection technology requires photodetectors with distinct properties. The choice of an adequate photodetecting system depends on its application, where aspects such as spectral selectivity, speed, and sensitivity play a critical role. High-sensitivity photodetection covering a large spectral range from the UV to IR is dominated by photodiodes. To overcome existing limitations in sensitivity and cost of state-of-the-art systems, new device architectures and material systems are needed with low-cost fabrication and high performance. Low-dimensional nanomaterials (0D, 1D, 2D) are promising candidates with many unique electrical and optical properties and additional functionalities such as flexibility and transparency. In this Perspective, the physical mechanism of photo-FETs (field-effect transistors) is described and recent advances in the field of low-dimensional photo-FETs and hybrids thereof are discussed. Several requirements for the channel material are addressed in view of the photon absorption and carrier transport process, and a fundamental trade-off between them is pointed out for single-material-based devices. We further clarify how hybrid devices, consisting of an ultrathin channel sensitized with strongly absorbing semiconductors, can circumvent these limitations and lead to a new generation of highly sensitive photodetectors. Recent advances in the development of sensitized low-dimensional photo-FETs are discussed, and several promising future directions for their application in high-sensitivity photodetection are proposed.Peer ReviewedPostprint (author's final draft

Radiation effects on two‐dimensional materials

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135401/1/pssa201600395_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135401/2/pssa201600395.pd

Dual Gate Black Phosphorous Photodetectors Using a Polymer Electrolyte for Integrated Photonics and Optoelectronics Applications

Les photodétecteurs occupent une place prépondérante dans un nombre important de dispositifs. Ceux-ci sont utilisés dans plusieurs pour les communications optiques, la détection d'images, la vision nocturne, l’inspection alimentaire, l’imagerie médicale, etc. La conception de détecteurs infrarouges requiert l’utilisation de matériaux autre que le silicium démontrant une haute efficacité, détectivité et un temps de réponse rapide. Ceux-ci sont typiquement couteux et difficiles à intégrés avec des substrats flexibles ou des circuits photoniques et optoélectroniques conventionnels. Dans cette thèse, nous présentons un photodétecteur à base de phosphore noir avec une architecture à double grille basé sur sur un électrolyte polymère solide pour des applications en photonique intégrée et en optoélectronique. La combinaison de la grille électrolytique et du photodétecteur BP conventionnel permet un contrôle efficace du transport électrique et de la modulation de la densité de porteurs dans le canal BP. Les détecteurs à double grille fabriqués avec cette approche améliorent le rapport ON / OFF de 50 fois par rapport à l’architecture conventionnelle. Ceux-ci présentent également du courant de drain avec la configuration de contact source-drain orthogonale. Finalement, l’électrolyte polymère protège les flocons de BP de l'oxydation de surface et présentent des caractéristiques électriques stables dans les conditions ambiantes. Nous obtenons une modulation du photocourant par un facteur de 4 pour des puissances incidentes variant de 0.5 mW à 5 mW. Dans cette gamme de puissance, une modulation du photocourant par un facteur de 2 est obtenu en variant la tension de grille supérieure (variée de 3V à -3V) à une longueur d'onde de 808 nm. À plus faible puissance, le photodétecteur donne une modulation de photocourant largement supérieure à l’architecture conventionnelle: environ 16 fois avec une tension de grille d'électrolyte ajustée de -2 V à 2 V par rapport au dispositif à grille inférieure qui est d'environ 2.5 fois avec une tension de grille variant de -10 V 10 V dans le proche infrarouge. Des sensibilités de centaines de mA / W sont obtenues pour les photodétecteurs BP dans les régimes visible et proche-infrarouge.----------Abstract Visible and infrared photodetectors have become important in a multitude of present-day devices that find emerging applications in several fields: optical communications, image sensing, night vision, food monitoring and medical imaging etc. However, photodetection beyond the visible region of spectrum requires investigating unconventional materials and designs that deliver superior performance in terms of photocurrent/responsivity, detectivity and response speed, that also allow ultra-low weight, low-cost, flexible and easy integration with the photonic and optoelectronic circuits. In this thesis, we report on a dual-gate black phosphorous photodetector based on solid polymer electrolyte for integrated photonics and optoelectronic applications. The combination of polymer electrolyte gate with the conventional back-gate black phosphorous (BP) photodetector allows for efficient control of electrical transport and carrier-density modulation in the BP channel. Our dual-gate field effect transistors provide a 50-fold enhancement in the drain currents that lead to high ON/OFF ratio as compared to the conventional SiO2 bottom gating. The BP FETs with polymer electrolyte film also protect BP flake from surface oxidation and show stable electrical characteristics under ambient conditions. The polymer electrolyte-based FETs also show an enhancement in the drain current with the orthogonal source-drain contact configuration. Photocurrent modulation by a factor of four by incident powers (varied from 0.5 to 5 mW) at a wavelength of 808 nm. At these modest powers, a factor of two modulation in the photocurrent is achieved by varying the top-gate voltage (from 3 V to -3 V). At lower powers, the dual-gate polymer electrolyte based BP photodetector shows a photocurrent a substantial enhancement of the photocurrent by 16 when the electrolyte gate voltage tuned from -2 V to 2 V as compared to the bottom gate device which is 2.5 times, when the gate voltage varied from -10 V to 10 V. Responsivities of the order of hundreds of mA/W are obtained for the BP photodetectors in both visible and NIR regimes

THERMAL AND PHOTOELECTRIC TRANSPORT IN NOVEL TWO-DIMENSIONAL MATERIALS

Ph.DDOCTOR OF PHILOSOPH

Optoelectronic properties of the two-dimensional van der Waals semiconductor indium selenide (InSe)

This thesis presents an investigation of the optoelectronic properties of the two-dimensional (2D) van der Waals (vdW) semiconductor indium selenide (InSe) and exploits these properties in InSe-graphene vdW heterostructure devices. These heterostructures are fabricated by mechanical exfoliation and dry transfer of InSe and graphene nanosheets. A novel method of device fabrication by needle transfer of graphene microsheets is also described and used for some devices. The optical properties of InSe nanosheets differ qualitatively from those reported for other 2D materials, such as transition metal dichalcogenides (TMDCs). In particular, this thesis reports on the controlled modulation of optical signals by exploiting the inherent optical anisotropy and mechanical flexibility of atomically thin 2D vdW InSe bent onto a periodic array of silicon (Si) nanopillars. A series of vertical and planar vdW heterostructures, including tunnelling transistors and photodetectors, are investigated. The optoelectronic transport characteristics of these devices exploit a favourable band alignment between InSe and graphene. Moreover, 2D energy subbands of InSe exhibit strong quantum confinement, offering a route to the modulation of electrical properties. Optical absorption studies on bulk InSe by variable angle spectroscopic ellipsometry (VASE) are presented, which indicates strong resonances in the ultra-violet (UV) range of the absorption spectrum. A fast, ultra-high photoresponsivity is demonstrated in a hybrid phototransistor based on an InSe/graphene heterostructure that exploits the light-induced charge transfer at the interface of InSe and graphene

Multi-Functional Optoelectronic Heterostructure Devices Based on Transfer Printing of Nanomaterials

School of Energy and Chemical Engineering (Energy Engineering)Heterostructure devices, combining different electronic properties of semiconductors, offer novel electronic functionalities, which are critically required in emerging applications in high performance and multi-functional electronics. Previously, heterostructure devices have attracted a great attention due to the enhancing performances, adding functionalities and broadening absorption range, through components modulation, resulting in many applications in high electron mobility transistors, non-volatile memory, light emitting diodes, and broadband photodetectors. However, traditional semiconductor heterostructures present significant challenges due to the lattice constant mismatch with other substrates and generation of defects during the direct growth and deposition processes. To address these challenges, a transfer printing was introduced to heterogeneously integrate various nanomaterials onto arbitrary substrates, whereby the bonding at heterointerfaces with a large lattice mismatch is facilitated by van der Waals forces during the transfer printing processes. The transfer printing can provide a freedom of material choice, from zero to three dimensional materials, in the formation of heterostructures without the restriction from lattice mismatch, which enabled various heterostructure devices with unique physical properties. In this thesis, we demonstrate multi-functional optoelectronic heterostructure devices based on transfer printing of nanomaterials. First, in chapter 1, we briefly introduce the research trends in electronic devices and basic concept of transfer printing methods and multi-functional heterostructure devices. In chapter 2, we demonstrate a new type of heterostructure device based on black phosphorus and n-InGaAs nanomembrane semiconductors. The device offers gate-tunable rectification and switching behaviors. In addition, the proposed heterojunction diode can be programed by the modulation of forward current due to the capacitive gating effect. Furthermore, the device is photoresponsive in a spectral range spanning the ultraviolet to near infrared. In chapter 3, we describe the fine patterning technique of silver nanowires on various substrates using vacuum filtration and transfer printing process. This technique provides very simple and cost-effective fabrication for fine patterning of AgNWs electrode for optically transparent and mechanically flexible optoelectronic device applications. This patterning technique can be applied to other nanomaterials such as CNT and graphene and combination of nanomaterials to realize highly flexible and transparent optoelectronic devices. In chapter 4, the large-area MoS2 film and pattering process is demonstrated by shadow mask assisted transfer printing process. The liquid exfoliated MoS2 flakes can be easily patterned by vacuum filtration with polyimide shadow mask. Patterned film is transferred to arbitrary substrate by using transfer printing process for high performance and flexible electronic applications. Therefore, the heterostructure devices made by transfer printing are advantageous in scalability and avoids complicated fabrication process for multi-functional applications.ope

CHARGE AND SPIN TRANSPORT STUDIES IN GRAPHENE AND BLACK PHOSPHORUS

Ph.DDOCTOR OF PHILOSOPH

Colossal Ultraviolet Photoresponsivity of Few-Layer Black Phosphorus

Black phosphorus has an orthorhombic layered structure with a layer-dependent direct band gap from monolayer to bulk, making this material an emerging material for photodetection. Inspired by this and the recent excitement over this material, we studied the optoelectronics characteristics of high-quality, few-layer black phosphorus-based photodetectors over a wide spectrum ranging from near-ultraviolet (UV) to near-infrared (NIR). It is demonstrated for the first time that black phosphorus can be configured as an excellent UV photodetector with a specific detectivity ∼3 × 10¹³ Jones. More critically, we found that the UV photoresponsivity can be significantly enhanced to ∼9 × 10⁴ A W^–1 by applying a source-drain bias (<i>V</i>_SD) of 3 V, which is the highest ever measured in any 2D material and 10⁷ times higher than the previously reported value for black phosphorus. We attribute such a colossal UV photoresponsivity to the resonant-interband transition between two specially nested valence and conduction bands. These nested bands provide an unusually high density of states for highly efficient UV absorption due to the singularity of their nature