Creat membership Creat membership
Sign in

Forgot password?

Confirm
  • Forgot password?
    Sign Up
  • Confirm
    Sign In
home > search

Now showing items 1 - 16 of 50

  • Emerging technologies for high performance infrared detectors

    Tan, Chee Leong   Mohseni, Hooman  

    Infrared photodetectors (IRPDs) have become important devices in various applications such as night vision, military missile tracking, medical imaging, industry defect imaging, environmental sensing, and exoplanet exploration. Mature semiconductor technologies such as mercury cadmium telluride and III-V material-based photodetectors have been dominating the industry. However, in the last few decades, significant funding and research has been focused to improve the performance of IRPDs such as lowering the fabrication cost, simplifying the fabrication processes, increasing the production yield, and increasing the operating temperature by making use of advances in nanofabrication and nanotechnology. We will first review the nanomaterial with suitable electronic and mechanical properties, such as two-dimensional material, graphene, transition metal dichalcogenides, and metal oxides. We compare these with more traditional low-dimensional material such as quantum well, quantum dot, quantum dot in well, semiconductor superlattice, nanowires, nanotube, and colloid quantum dot. We will also review the nanostructures used for enhanced lightmatter interaction to boost the IRPD sensitivity. These include nanostructured antireflection coatings, optical antennas, plasmonic, and metamaterials.
    Download Collect
  • Engineering the gain-bandwidth product of phototransistor diodes

    Bianconi, Simone   Rezaei, Mohsen   Park, Min-Su   Huang, Wenyuan   Tan, Chee Leong   Mohseni, Hooman  

    In recent years, phototransistors have considerably expanded their field of application, including for instance heterodyne detection and optical interconnects. Unlike in low-light imaging, some of these applications require fast photodetectors that can operate in relatively high light levels. Since the gain and bandwidth of phototransistors are not constant across different optical powers, the devices that have been optimized for operation in low light level cannot effectively be employed in different technological applications. We present an extensive study of the gain and bandwidth of short-wavelength infrared phototransistors as a function of optical power level for three device architectures that we designed and fabricated. The gain of the photodetectors is found to increase with increasing carrier injection. Based on a Shockley-Read-Hall recombination model, we show that this is due to the saturation of recombination centers in the phototransistor base layer. Eventually, at a higher light level, the gain drops, due to the Kirk effect. As a result of these opposing mechanisms, the gain-bandwidth product is peaked at a given power level, which depends on the device design and material parameters, such as doping and defect density. Guided by this physical understanding, we design and demonstrate a phototransistor which is capable of reaching a high gain-bandwidth product for high-speed applications. The proposed design criteria can be employed in conjunction with the engineering of the device size to achieve a wide tunability of the gain and bandwidth, hence paving the way toward fast photodetectors for applications with different light levels. Published under license by AIP Publishing.
    Download Collect
  • Sensitivity Limit of Nanoscale Phototransistors

    Rezaei, Mohsen   Park, Min-Su   Tan, Chee Leong   Mohseni, Hooman  

    In this letter, the optical gain mechanism in phototransistor detectors (PTDs) is explored in low light conditions. An analytical formula is derived for the physical limit on the minimum number of detectable photons for the PTD. This formulation shows that the sensitivity of the PTD, regardless of its material composition, is related to the square root of the normalized total capacitance at the base layer. Since the base total capacitance is directly proportional to the size of the PTD, the formulation shows the scaling effect on the sensitivity of the PTD. Our proposed model can be used to explore a wide range of PTDs, including nanowire, monolayer, and bulk devices. For the illustration of the ability of the model, two different PDTs, one with bottom-up fabrication for ultraviolet and the other with top-down fabrication for short-wave infrared (SWIR) detection, are used. For the SWIR PTD, a scaling effect is explored on InGaAs-based devices. Our modeling predicts that this PTD with a nanoscale electronic area can reach to a single photon noise equivalent power even at room temperature. To the best of our knowledge, this is the first comprehensive study on the sensitivity of the PTD for extreme low light detection.
    Download Collect
  • Heterojunction phototransistor for highly sensitive infrared detection

    Rezaei, Mohsen   Park, Min-Su   Tan, Chee Leong   Rabinowitz, Cobi   Wheaton, Skyler   Mohseni, Hooman  

    In this work, we have proposed a model for the ultimate physical limit on the sensitivity of the heterojunction bipolar phototransistors (HPTs). Based on our modeling we have extracted the design criteria for the HPT for high sensitivity application. HPT with the submicron emitter and base area has the potential to be used for the low number photon resolving in near-infrared (NIR) wavelength. However, in practice, the quality of materials, processing, and the passivation plays an important role in the realization of the highly sensitive HPT. For short wave infrared (SWIR) HPTs based on lattice matched InGaAs to InP is studied. For these devices, conditions to reach to the highest possible sensitivity is examined. We have made an HPT based on InGaAs collector and base on the InP substrate. After developing proper processing combination of wet and dry etching and the surface passivation for the device we made an imager with 320x256 pixels based with a 30m pixel pitch. The imager shows the sensitivity less the 30 photons for each pixel with the frame rate more than 1K frames per second.
    Download Collect
  • Emerging technologies for high performance infrared detectors

    Tan, Chee Leong   Mohseni, Hooman  

    Download Collect
  • Absorption enhancement of 980 nm MSM photodetector with a plasmonic grating structure

    Tan, Chee Leong   Lysak, Volodymyr V.   Alameh, Kamal   Lee, Yong Tak  

    We present finite-difference time-domain (FDTD) simulation to analyze the optical absorption enhancement of metal-semiconductor-metal (MSM) photodetectors employing plasmonic grating structures. Simulation results show that the combination of a subwavelength aperture and a nano-structured metal grating results in up to 16 times enhancement in optical absorption, in comparison to conventional MSM photodetector structures employing only a subwavelength aperture. (C) 2009 Elsevier B.V. All rights reserved.
    Download Collect
  • High-efficiency light-trapping effect using silver nanoparticles on thin amorphous silicon subwavelength structure

    Tan, Chee Leong   Lee, Yong Tak  

    Download Collect
  • High-efficiency light-trapping effect using silver nanoparticles on thin amorphous silicon subwavelength structure

    Tan, Chee Leong   Lee, Yong Tak  

    In this Letter, we experimentally demonstrate a hybrid structure consisting of metal nanoparticles deposited onto a subwavelength structure (SWS), which further increases the absorption of thin amorphous silicon (a-Si) and can possibly lead to a reduction in the minimum required thickness of the a-Si layer. Experimental results show that backscattering of the silver nanoparticles (Ag NPs) deposited on the top surface can be suppressed dramatically (by 85.5%) by the Ag NPs deposited on the SWS. We also experimentally prove that the thin a-Si SWS only lowers the surface reflectivity and does not increase the absorption rate of the material. The absorption of the thin a-Si layer can be increased by depositing Ag NPs onto a thin a-Si SWS, which not only reduces the backscattering of the metal NPs but also increases the light-trapping effect within thin a-Si through localized surface plasmon resonance properties. This decrease of reflection and increase in the light-trapping effect of Ag NPs on cone-shaped thin a-Si SWSs leads to extremely high average absorption (86.14%) within a 400 nm thick a-Si layer. (C) 2013 Optical Society of America
    Download Collect
  • AuAg bimetallic nonalloyed nanoparticles on a periodically nanostructured GaAs substrate for enhancing light trapping

    Lee, Soo Kyung   Tan, Chee Leong   Ju, Gun Wu   Song, Jae Hong   IlYeo, Chan   Lee, Yong Tak  

    We present a light trapping structure consisting of AuAg bimetallic nonalloyed nanoparticles (BNNPs) on coneshaped GaAs subwavelength structures (SWSs), combining the advantages of plasmonic structures and SWSs for GaAs-based solar cell applications. To obtain efficient light trapping in solar cells, the optical properties' dependence on the size and composition of the Ag and Au metal nanoparticles was systematically investigated. Cone-shaped GaAs SWSs with AuAg BNNPs formed from an Au film of 12 nm and an Ag film of 10 nm exhibited the extremely low average reflectance (R-avg) of 2.43% and the solar-weighted reflectance (SWR) of 2.38%, compared to that of a bare GaAs substrate (R-avg, 37.50%; SWR, 36.72%) in the wavelength range of 300 to 870 nm. (C) 2015 Optical Society of America
    Download Collect
  • InGaAs/InP quantum well infrared photodetector integrated on Si substrate by Mo/Au metal-assisted wafer bonding

    Park, Min-Su   Rezaei, Mohsen   Nia, Iman   Brown, Robert   Bianconi, Simone   Tan, Chee Leong   Mohseni, Hooman  

    Integration of an InGaAs/InP quantum well infrared photodetector (QWIP) onto a Si substrate was successfully demonstrated via a metal-assisted wafer bonding (MWB) using a Mo/Au metal scheme. The Mo/Au/Mo layer, situated between the QWIP structure and the Si, has shown a well-ordered lamination. It provides a smooth surface with a roughness of about 0.8 nm, as measured by a scanning electron microscope (SEM) and atomic force microscopy (AFM). The results on crystalline quality evaluated by Raman spectroscopy and X-ray diffraction (XRD) imply that the MWB could be achieved without any measurable material degradation and residual strain. Temperature dependence of dark current revealed that there is no noticeable change in the dark current properties of the QWIP after bonding on Si, despite that the quantum wells are only 200 nm away from the bonding interface. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
    Download Collect
  • InGaAs based heterojunction phototransistors:Viable solution for high-speed and low-noise short wave infrared imaging

    Rezaei, Mohsen   Park, Min-Su   Rabinowitz, Cobi   Tan, Chee Leong   Wheaton, Skylar   Ulmer, Melville   Mohseni, Hooman  

    Highly sensitive and fast imaging at short-wavelength infrared (SWIR) is one of the key enabling technologies for the direct-imaging of habitable exoplanets. SWIR imaging systems currently available in the market are dominated by imagers based on InGaAs PIN photodiodes. The sensitivity of these cameras is limited by their read-out noise (RON) level. Sensors with internal gain can suppress the RON and achieve lower noise imaging. In this paper, we demonstrate a SWIR camera based on 3D-engineered InP/InGaAs heterojunction phototransistors with responsivities around 2000A/W which provides a shot-noise limited imaging sensitivity at a very low light level. We present the details of the semiconductor structure, the microfabrication, and the heterogeneous integration of this camera. The low capacitance pixels of the imager achieve 36 electron effective RON at frame rates around 5 kilo-frames per second at an operating temperature of 220 K and a bias voltage of 1.1 V. This is a significant step toward achieving highly sensitive imaging at SWIR at high frame rates and noncryogenic operating temperatures. Based on the proposed modeling and experimental results, a clear path to reach the RON less than 10 electrons is presented. Published under license by AIP Publishing.
    Download Collect
  • InGaAs based heterojunction phototransistors: Viable solution for high-speed and low-noise short wave infrared imaging

    Rezaei, Mohsen   Park, Min-Su   Rabinowitz, Cobi   Tan, Chee Leong   Wheaton, Skylar   Ulmer, Melville   Mohseni, Hooman  

    Download Collect
  • Bi-SERS sensing and enhancement by Au-Ag bimetallic non-alloyed nanoparticles on amorphous and crystalline silicon substrate

    Tan, Chee Leong   Lee, Soo Kyung   Lee, Yong Tak  

    We have demonstrated Au-Ag bimetallic non-alloy nanoparticles (BNNPs) on thin a-Si film and c-Si substrate for high SERS enhancement, low cost, high sensitivity and reproducible SERS substrate with bi-SERS sensing properties where two different SERS peak for Au NPs and Ag NPs are observed on single SERS substrate. The isolated Au-Ag bimetallic NPs, with uniform size and spacing distribution, are suitable for uniform high density hotspot SERS enhancement. The SERS enhancement factor of Au-Ag BNNPs is 2.9 times higher compared to Ag NPs on similar substrates due to the increase of the localized surface plasmon resonance effect. However there is a decrement of SERS peak intensity at specific wavenumbers when the surrounding refractive index increases due to out-phase hybridization of Au NPs. The distinct changes of the two different SERS peaks on single Au-Ag BNNPs SERS substrate due to Au and Ag NPs independently show possible application for bi-molecular sensing. (C) 2015 Optical Society of America
    Download Collect
  • Broadband high responsivity large-area plasmonic-enhanced multilayer MoS2 on p-type silicon photodetector using Au nanostructures

    Tan, Chee Leong   Wei, Heming   Thandavam, Tamil Many K.   Ramli, Rizal   Park, Minsu   Ahmad, Harith  

    High responsivity, large-area plasmonic-enhanced nanostructure photodetector based on multilayer (ML) molybdenum disulfide (MoS2) deposited on p-type Silicon (Si) substrates is reported. A large area ML-MoS2 is deposited onto the Si photodetector (PD) using a modified membrane filtration method. This large area ML-MoS2 and Au NSs on the p-Si form a cavity-like structure that dramatically enhances the incident light path. The increase of incident light path due to light trapping effect enhances the electron-hole pair generation tremendously. The plasmonic-enhanced ML MoS2 on Si PD has achieved a stable and repeatable photoresponse up to 37 A W-1, whereas the detectivity is around 10(12) Jones at the broad wavelengths (405-780 nm) with a modulation frequency of 1 kHz. The enhancement of photoresponsivity is 8, 5.3 and 11 times with 5 V bias at an incident wavelength of 405 nm, 650 nm and 780 nm respectively as compared to the bare p-Si PD. The experimental results also show that the plasmonic-enhanced ML-MoS2 on Si PD exhibited fast photoresponse (rise time of similar to 1 mu s and fall time of similar to 18 mu s), which is much higher compared to typical transition metal dichalcogenide PD or single layer MoS2 based PD. These excellent performances show that the plasmonic-enhanced MoS2 structure is highly potential to apply in Si photovoltaics, visible range photodetection, and visible bio/chemical sensing application.
    Download Collect
  • AuAg Bimetallic Non-Alloyed Nanoparticles on SiO2 Spacer Layer for Improved Light Absorption in Thin-Film c-Si Solar Cells

    Lee, Soo Kyung   Lim, Hee-Jin   Tan, Chee Leong   Lee, Yong Tak  

    We present a light trapping structure consisting of gold and silver (AuAg) bimetallic non-alloyed nanoparticles (BNNPs) on a silicon dioxide (SiO2) spacer layer over crystalline silicon (c-Si) film, designed to improve the absorption of thin-film c-Si solar cells. Prior to fabrication of the AuAg BNNPs on the SiO2 spacer layer, numerical investigations were carried out using electromagnetic field simulation following the finite-difference time-domain method. The hemispherical Au8Ag8 BNNPs were fabricated and deposited on a 15 nm-thick SiO2 spacer layer, which enhanced light trapping in the c-Si film over a broad wavelength range (450-1100 nm). Specifically, more than 85% of the incident light was absorbed in the c-Si film at 620 nm wavelengths due to the strong scattering of the Au8Ag8 BNNPs. To the best of our knowledge this is the first case presenting such a theoretical calculation and experimental study of the efficient light trapping by AuAg BNNPs on space layer for increasing the absorption in thin-film c-Si solar cells.
    Download Collect
  • Localized surface plasmon resonance with broadband ultralow reflectivity from metal nanoparticles on glass and silicon subwavelength structures

    Tan, Chee Leong   Jang, Sung Jun   Lee, Yong Tak  

    Metal nanoparticles (NPs) are well known to increase the efficiency of photovoltaic devices by reducing reflection and increasing light trapping within device. However, metal NPs on top flat surface suffer from high reflectivity losses due to the backscattering of the NPs itself. In this paper, we experimentally demonstrate a novel structure that exhibits localized surface plasmon resonance (LSPR) along with broadband ultralow reflectivity over a wide range of wavelength. Experimental results show that by depositing Ag NPs and Au NPs onto glass subwavelength structures (SWS) the backscattering effect of NPs can be suppressed, and the reflections can be considerably reduced by up to 87.5% and 66.7% respectively, compared to NPs fabricated on a flat glass substrate. Broadband ultralow reflection (< 2%) is also observed in the case of Ag NPs and Au NPs fabricated on cone shaped SWS silicon substrate over a wavelength range from 200 nm to 800 nm. This broadband ultralow reflectivity of Ag NPs and Au NPs on silicon SWS structure leads to a substantial enhancement of average absorption by 66.53% and 66.94%, respectively, over a broad wavelength range (200-2000 nm). This allows light absorption by NPs on SWS silicon structure close to 100% over a wavelength range from 300 nm to 1000 nm. The mechanism responsible for the increased light absorption is also explained.
    Download Collect
1 2 3 4

Contact

If you have any feedback, Please follow the official account to submit feedback.

Turn on your phone and scan

Submit Feedback