On-chip graphene optoelectronic devices for high-speed modulation and photodetection

There has been a rapidly growing interest in graphene-based optoelectronics. This exceptional material exhibits broadband optical response, ultrahigh carrier mobility and more importantly, potential compatibility with silicon complementary metal-oxide semiconductor (CMOS) technology. Here we present our recent works that integrate graphene with silicon channel waveguides and photonic crystal cavities. By coupling graphene to an optical cavity, we demonstrated an efficient electro-optic modulator that features a modulation depth of 10 dB and a switching energy of 300 fJ. Several high-speed modulators are also tested, showing a speed up to 0.57 GHz. In addition, we implemented a graphene photodetector on a silicon waveguide. The 53-μm-long graphene channel couples to the evanescent field of the waveguide mode, resulting in more than 60% absorption of the input light. We demonstrated a responsivity of 0.108 A/W in our photodetector. A data transmission of 12 Gbps and response time in excess of 20 GHz are also achieved. These results show the feasibility of graphene as a building block for silicon photonic integrated circuits. In particular, on-chip graphene active devices such as modulators and photodetectors are promising for their broadband response, high-speed operation, low power consumption and ease-to-fabrication.United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0001088

Enhanced Photodetection in Graphene-Integrated Photonic Crystal Cavity

We demonstrate the controlled enhancement of photoresponsivity in a graphene photodetector by coupling to slow light modes in a long photonic crystal linear defect cavity. Near the Brillouin zone (BZ) boundary, spectral coupling of multiple cavity modes results in broad-band photocurrent enhancement from 1530 nm to 1540 nm. Away from the BZ boundary, individual cavity resonances enhance the photocurrent eight-fold in narrow resonant peaks. Optimization of the photocurrent via critical coupling of the incident field with the graphene-cavity system is discussed. The enhanced photocurrent demonstrates the feasibility of a wavelength-scale graphene photodetector for efficient photodetection with high spectral selectivity and broadband response

High-Responsivity Graphene-Boron Nitride Photodetector and Autocorrelator in a Silicon Photonic Integrated Circuit

Graphene and other two-dimensional (2D) materials have emerged as promising materials for broadband and ultrafast photodetection and optical modulation. These optoelectronic capabilities can augment complementary metal-oxide-semiconductor (CMOS) devices for high-speed and low-power optical interconnects. Here, we demonstrate an on-chip ultrafast photodetector based on a two-dimensional heterostructure consisting of high-quality graphene encapsulated in hexagonal boron nitride. Coupled to the optical mode of a silicon waveguide, this 2D heterostructure-based photodetector exhibits a maximum responsivity of 0.36 A/W and high-speed operation with a 3 dB cut-off at 42 GHz. From photocurrent measurements as a function of the top-gate and source-drain voltages, we conclude that the photoresponse is consistent with hot electron mediated effects. At moderate peak powers above 50 mW, we observe a saturating photocurrent consistent with the mechanisms of electron-phonon supercollision cooling. This nonlinear photoresponse enables optical on-chip autocorrelation measurements with picosecond-scale timing resolution and exceptionally low peak powers

Chalcogenide Glass-on-Graphene Photonics

Two-dimensional (2-D) materials are of tremendous interest to integrated photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. In this paper, we present a new route for 2-D material integration with planar photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides claiming improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as graphene-based mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators

The poly-Si Thin Film Transistor and a-Si:H p-i-n Solar Cell for 4x4 Energy-Recycling Organic Light Emitting Diode Array

在本論文中，先探討兩種元件的特性包括用準分子雷射退火的多晶矽薄膜電晶體以及非晶矽p-i-n太陽能電池。太陽能電池被導入在薄膜電晶體和有機發光二極體之間以解決對比降低的問題。經由這種新的設計，太陽光和有機二極體所發出來的光都可以被太陽能電池所吸收，同時這兩種被回收的光也可以被視為一種新的能源來達成能量回收型的有機發光二極體。而以每個能量回收型單元為核心，將能量回收型元件中薄膜電晶體連接成閘極的掃描線以及汲極的資料線的方式，擴展為能量回收型有機發光二極體的矩陣來展示此種能量回收型元件能應用在現今的面板產品中，特別是對於省電節能需求很高的可攜式的電子產品。三個元件的整合製程中需要運用低溫絕緣層a-SiNX薄膜以及特殊設計的有機發光二極體電極。最後，我們成功的製作出包含16組三種元件的4x4能量回收型有機發光二極體矩陣。The performance of poly-Si TFT fabricated by excimer laser annealing and the current-voltage characteristics of a-Si:H p-i-n solar cell were studied in the thesis. Solar cell was introduced between thin film transistor (TFT) and organic light emitting diode (OLED) to solve the contrast problem. Through the new design, both the sun light and the emitted light from OLED can be absorbed by the solar cell to achieve the energy-recycling OLED. By connecting every TFT drain with data lines and gate with scan lines, we will expand this energy-recycling device to a 4x4 energy-recycling array, which has practical applications in some mobile/portable electronic devices which are particularly power-aware. The integration of the three devices (TFT and OLED and solar cell) requires a low temperature a-SiNx passivation layer and a specially designed electrodes for OLED. Finally, the 4x4 energy-recycling OLED array consisting of 16 TFT, 16 solar cell and 16 OLEDs has been fabricated successfully.Contents Chapter 1 Introduction 1 Chapter 2 Experiments 5 2.1 Deposition System --Plasma Enhanced Chemical Vapor Deposition（PECVD）………………………..5 2.2 Substrate Preparation 8 2.3 Deposition Procedures 10 2.4 Measurement Techniques 11 2.4.1 Film Thickness 11 2.4.2 Current–Voltage Characteristics 12 2.4.3 Transmittance and Reflectance…………………………..12 2.4.4 Spectral Response………………………………………..12 2.4.5 Introduction of FTIR………………………………………….15 Chapter 3 Poly-Si Thin Film Transistor and a-Si:H p-i-n Solar Cell………………………..18 3.1 The fabrication of poly-Si TFT by ELA………18 3.2 The Performance of Poly-Si TFT by ELA…………23 3.3 The fabrication processes of a-Si:H p-i-n Solar Cell..23 3.4 Current-Voltage Characteristics of a-Si:H p-i-n SolarCell………………………………………25 Chapter 4 4x4 Energy-Recycling OLED array…………………………..35 4.1 The fabrication of 4x4 energy-recycling OLED array..............................................................................36 4.2 The Performance of TFT and a-Si:H p-i-n Solar Cell as a part of 4x4 energy-recycling array……………44 4.3 The 4x4 energy-recycling OLED array ……………55 Chapter 5 Conclusions 68 References 7

Heterogeneous integration of two-dimensional materials for on-chip optical interconnects

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.Cataloged from PDF version of thesis.Includes bibliographical references (pages 141-164).Two-dimensional materials have emerged as promising candidates to augment existing optical networks for metrology, sensing, and telecommunication. Their structural nature lends themselves remarkable flexibility to be conformally transferred and "glued" strongly onto arbitrary bulk semiconductor substrates by van der Waal forces. This offers a simple approach to construct heterogeneous photonic architectures, which is currently challenging for silicon-based photonics integrated with germanium and III-V semiconductors due to mismatched lattice constants and thermal properties. In addition, the entire family of 2D materials can exhibit a rich variety of physical behaviors, ranging from that of a wide-bandgap insulator to a narrow-gap semiconductor to a semimetal or metal. Previous demonstrations suggest that generic building blocks for a photonic integrated circuit including light sources, modulators, and photodetectors can be accomplished using 2D materials. Beyond conventional components, distinct 2D materials can form a variety of 2D heterostructures with high quality, enabling potential optoelectronic devices that were not feasible using silicon and other bulk semiconductors. In this dissertation, I present several classes of active photonic components in a 2D materials-based heterogeneous architecture. First, by depositing graphene onto silicon photonic crystal nanocavities, it is possible to reach near unity absorption into graphene. The cavity-graphene system enables a high-contrast (> 10 dB) electrooptic modulation by electrically tuning the Fermi level of graphene. High-speed modulation is possible using high-speed capacitive gating, such as through a double layer graphene stack encapsulated in 2D hexagonal boron nitride layers. The demonstrated modulation speed exceeds 1.2 GHz. The cavity also enables dramatically enhanced and spectrally selective photodetection in graphene. To further enable broadband photodetection, a similar scheme that couples graphene to the evanescent field of nanophotonic waveguides extends the interaction length of graphene with light dramatically, achieving high-speed (> 40 GHz) photodetection with high responsivity. The responsivity of the detector reaches a maximum (0.36 A/W) when the doping of graphene is controlled at a level that maximizes photothermoelectric, photovoltaic and bolometric effects in graphene. Finally, light sources based on cavity-integrated 2D molybdenum disulfide show pronounced fluorescence enhancement owing to the Purcell effect in an optical cavity. An electrically-driven thermal light source of graphene in a cavity provides a new route to control the thermal emission spectrum at a temperature beyond 2000 K. These heterogeneous architectures and devices combine the advantages of 2D materials and dielectric photonic structures, promising for an ease-of-fabrication, large-scale and high-performance optical interconnect.by Ren-Jye Shiue.Ph. D

High-Performance Flexible Waveguide-Integrated Photodetectors

Mechanically flexible photonic devices are essential building blocks for novel bio-integrated optoelectronic systems, wearable sensors, and flexible consumer electronics. Here we describe the design and experimental demonstration of high-performance flexible semiconductor nanomembrane photodetectors integrated with single-mode chalcogenide glass waveguides. Through a combination of a waveguide-integrated architecture to enhance light–matter interactions and mechanical engineering of multilayer configurations to suppress strains, the detector devices exhibit record optical and mechanical performance. The devices feature a noise equivalent power as low as 0.02 pW · Hz1/2, a linear dynamic range exceeding 70 dB, and a 3-dB bandwidth of 1.4 GHz, all measured at 1530 nm wavelength. The devices withstand 1000 bending cycles at a submillimeter radius without degradation in their optoelectronic responses. These metrics represent significant improvements over state-of-the-art flexible photodetectors