iru Gu

Optimizing light absorption in quantum dot infrared photodetectors by tuning surface confinement of surface plasmonic waves

In this paper, we measured the transmission of the 2DSHA surface plasmonic structures and its variation with the hole diameters a of the 2DSHA structures. The relationship between the transmission and the hole diameters a is found to be different from the prediction of Bethes diffraction theorem. We also found that the photocurrent of the quantum dot (QD) infrared photodetectors (QDIPs) with different QD active layer thicknesses show different dependence on the hole diameters a of the 2DSHA structures. The photocurrent of the QDIPs with 10 active QD layers (10-QDIPs) saturates and starts to decrease as the hole diameter a is larger than 1.6 µm, whereas that of the QDIPs with 20 active QD layers (20-QDIPs) increases linearly with the hole diameter. The difference in the hole-diameter dependence of the 10-QDIPs and the 20-QDIPs is attributed to the variation of the near-field spreading in the vertical (surface-normal) direction due to the change in the hole diameters. An over 6 time (6×) photocurrent enhancement is obtained by optimizing the hole diameter of the 2DSHA surface plasmonic structure.

A Fano-type interference enhanced quantum dot infrared photodetector

In this letter, we report a quantum dot photodetector enhanced by Fano-type interference in a metallic two-dimensional (2D) subwavelength hole array (2DSHA). The photocurrent enhancement wavelength shows an offset from the plasmonic resonant peak and corresponds to a dip in the transmission spectrum of the 2DSHA structure. The offset is attributed to the Fano-type interference in the 2DSHA structure. The asymmetric line shapes of the plasmonic resonance are analyzed and agree well with the two-peak Fano-type interference model. Over 100% enhancement in photodetectivity and photoresponsivity is achieved at the wavelength of the Fano dip of the first order plasmonic mode.

Surface plasmonic resonance induced near-field vectors and their contribution to quantum dot infrared photodetector enhancement

In this paper, we analyse surface plasmonic resonance (SPR) induced near-field electric-field vector distribution in the quantum dot (QD) region and determine their roles in quantum dot infrared photodetector (QDIP) enhancement. SPR can be excited in metallic two-dimensional subwavelength hole arrays (2DSHAs) when illuminated at resonant wavelengths. The SPR induced near-field vectors (Ez, Ex and Ey) and their distributions and overlaps with the QD active region are simulated. A long-wave infrared (LWIR) QDIP is fabricated with the 2DSHA plasmonic structure to experimentally measure the SPR enhancement spectrum and compare it with the near-field vector components and their distribution in QDs. We found that QDIP enhancement is closely related to the near-field intensity overlap integral in the QD region. The large near-field overlap integral corresponds to high QDIP enhancement. Such near-field overlap integral dependent plasmonic enhancement is attributed to the interaction of and the electric-dipole interaction in QDs.

Surface plasmonic enhanced polarimetric longwave infrared photodetection with band pass spectral filtering

In this paper, we report a surface plasmonic enhanced polarimetric longwave infrared (LWIR) photodetector. Polarization-selective detection of LWIR incidence with different polarizations is achieved at different plasmonic resonant modes. Band-pass spectral filtering is also provided at the plasmonic resonant modes by the plasmonic enhancement. The extinction ratio (ER) of the polarimetric detection and its limiting factor is discussed.

Analysis of near-field components of a plasmonic optical antenna and their contribution to quantum dot infrared photodetector enhancement

In this paper, we analyze near-field vector components of a metallic circular disk array (MCDA) plasmonic optical antenna and their contribution to quantum dot infrared photodetector (QDIP) enhancement. The near-field vector components of the MCDA optical antenna and their distribution in the QD active region are simulated. The near-field overlap integral with the QD active region is calculated at different wavelengths and compared with the QDIP enhancement spectrum. The x-component (E(x)) of the near-field vector shows a larger intensity overlap integral and stronger correlation with the QDIP enhancement than E(z) and thus is determined to be the major near-field component to the QDIP enhancement.

Investigation of the humidity-dependent conductance of single-walled carbon nanotube networks

In this paper, we investigate the conductance of single walled carbon nanotube (SWCNT) networks at different humidity levels and various device temperatures. The carrier transport processes are analyzed by performing a temperature-dependent conductance study. It is found that the conductance of the SWCNT networks is dominated by the thermal activation carrier hopping over the barriers between CNTs. The average separation between the SWCNTs is found to vary linearly with the humidity levels. The humidity-dependent conductance of the SWCNT network is modeled and compared with the experimental data. The model agrees well with the experimental data.

A plasmonic dipole optical antenna coupled quantum dot infrared photodetector

In this paper, we report a full-wavelength plasmonic dipole optical antenna coupled quantum dot infrared photodetector (QDIP). The plasmonic dipole optical antenna can effectively modify the EM wave distribution and convert free-space propagation infrared light to localized surface plasmonic resonance (SPR) within the nanometer (nm) gap region of the full-wavelength dipole antenna. The plasmonic dipole optical antenna coupled QDIP shows incident-angle-dependent photocurrent enhancement. The angular dependence follows the far-field pattern of a full-wavelength dipole antenna. The directivity of the plasmonic dipole optical antenna is measured to be 1.8 dB, which agrees well with the antenna simulation. To our best knowledge, this is the first report of the antenna far-field and directivity measurement. The agreement of the detection pattern and the directivity with antenna theory confirms functions of an optical antenna are similar to that of a RF antenna.

A Printable CNT-Based FM Passive Wireless Sensor Tag on a Flexible Substrate With Enhanced Sensitivity

In this paper, we report a frequency-modulated (FM) passive wireless sensor tag for ammonia (NH3) sensing. The passive wireless sensor tag consists of a single-walled carbon nanotube (SWCNT) network based NH3 sensor, a radio frequency antenna, a ring oscillator, and other supporting circuits. The SWCNT network-based NH3 sensor is fabricated on a flexible plastic substrate through printable processes. The printable SWCNT-based NH3 sensor shows an enhanced sensitivity of 0.76% per part per million primarily due to the large surface area of the SWCNT network. The sensor also exhibits a high linearity between the resistance of the sensor and logarithm of the NH3 concentration (referred to as log [NH3] henceforth). A simple FM circuit is designed to convert the resistance change of the sensor to the oscillating frequency shift of the circuit. By properly designing the circuit, we have obtained a linear response between the frequency shift and log [NH3]. The linear response allows one to precisely predict the NH3 concentration by measuring the frequency shift of the FM wireless sensor tag. Such an FM-modulated passive wireless sensor tag with linear response and enhanced sensitivity is promising for power-less stand-alone low-level NH3 sensing and monitoring with high accuracy.

Quantum selection rule dependent plasmonic enhancement in quantum dot infrared photodetectors

In this paper, we analyze quantum selection rules of intersubband transitions in quantum dots (QDs) and determine their impact on plasmonic enhancement in quantum dot infrared photodetectors (QDIPs). Photoluminescence and photocurrent spectrum measurement were performed on QD samples with different doping levels to identify the QD energy levels and associate the photodetection peaks with the intersubband transitions. The quantum selection rules of the intersubband transitions are determined by the electric-dipole interaction. To determine the impact of quantum selection rules on the plasmonic enhancement, we fabricated metallic two-dimensional subwavelength hole array (2DSHA) plasmonic structures with different periods on QDIPs for specific plasmonic enhancement of individual intersubband transitions. We found that the plasmonic enhancement ratios of different intersubband transitions are not the same. The unequal enhancement ratios are attributed to the quantum selection rules in the intersubband transit...

All-Printed Thin-Film Transistor Based on Purified Single-Walled Carbon Nanotubes with Linear Response

We report an all-printed thin-film transistor (TFT) on a polyimide substrate with linear transconductance response. The TFT is based on our purified single-walled carbon nanotube (SWCNT) solution that is primarily consists of semiconducting carbon nanotubes (CNTs) with low metal impurities. The all-printed TFT exhibits a high ON/OFF ratio of around 103 and bias-independent transconductance over a certain gate bias range. Such bias-independent transconductance property is different from that of conventional metal-oxide-semiconductor field-effect transistors (MOSFETs) due to the special band structure and the one-dimensional (1D) quantum confined density of state (DOS) of CNTs. The bias-independent transconductance promises modulation linearity for analog electronics.