Elsevier

Sensors and Actuators A: Physical

Volume 229, 15 June 2015, Pages 166-171
Sensors and Actuators A: Physical

Highly sensitive room temperature infrared hybrid organic-nanocrystal detector

https://doi.org/10.1016/j.sna.2015.03.031Get rights and content

Highlights

  • The sensitivity of based QD detector was improved.

  • The photosensitive device exhibits a very high photoresponsivity.

  • The signal-to-noise ratio enables high sensitivity to very low photon powers.

  • Depletion of the surface states can be a way to increase the sensitivity.

  • The results were compared with simulations modeling program.

Abstract

In this paper we demonstrate a very sensitive near-infrared light detector device based on InAs nano crystals (NCs) acting as an optical gate on top of a high-mobility shallow two-dimensional electron gas channel. The ability to integrate electronics with the NCs using both top-down and bottom-up approaches allows to utilize the NCs unique quantum properties for future optoelectronic devices. We employ wet chemistry to self-assemble the organic monolayers and the NCs on top of the field effect transistor. By using shallow and very narrow channel, the device's quantum efficiency can go as high as 106 V/W at room temperature, with a signal-to-noise ratio that enables sensitivity for very low photon power. We find that our experimental results are compatible with simulation. Lastly, the route to advance to the single photon detection limit is discussed.

Introduction

Semiconductor GaAs-based devices are used for light-emitting diodes (LEDs) in optical communications and control systems, field effect transistors (FETs), and integrated circuits [1], [2], [3], [4], [5]. These devices utilize two main advantages of the GaAs/AlGaAs system: GaAs devices’ high mobility [6], and the fact that complicated band gap engineering can be easily accomplished by epitaxial growth [7].

Optoelectronic devices requiring high speed, together with photon counting abilities, have been extensively studied in recent years [8], [9], [10]. Most of the studies focus on the visible range wavelengths [11], [12], [13]. The development of a fast and sensitive room temperature detector in the infrared (IR) region has been elusive. Graphene grown by chemical vapor deposition has shown a very fast response but low responsivity of the order of 0.01 A/W measured at as low as 20 K in the IR region [14]. While reduced graphene oxide showed improved responsivity of ∼0.7 A/W in the infrared photoresponses [15], its main drawback lies in its slow response time of around 2 s. Another category of sensitive photon counting detectors is the InGaAs avalanche photon diodes (APD). While these detectors exhibit high performance at slightly cooled temperatures of around 250 K in the short wave IR range (incident photon counting at 1500 nm wavelength was demonstrated) [16], [17], [8], the cooling complicates the system, and the wavelength control is somewhat limited.

By coupling semiconductor nanocrystals (NCs), often called quantum dots, to a field effect transistor (FET), we have previously shown that a room temperature spectrally tunable light detector can be realized [18], [19], [20]. Nano-structures are unique since their energy levels depend on their size, structure, and composition. Hence, it is possible to control their electronic and optical properties and in particular, the absorption and/or emission wavelengths by modifying their composition or sizes [21], [22], [23]. When the NCs absorb light, charge or energy, separation occurs that creates a dipole moment that changes the current flowing through the transistor.

In this work we present a highly sensitive near-infrared light detector device based on InAs NCs acting as an optical gate on top of a high-mobility shallow two-dimensional electron gas channel. Our basic device's platform uses the GaAs/AlGaAs system's main advantages to develop a shallow field effect transistor together with adsorbed nano particles generating a highly sensitive room temperature detector. The selective absorbance of the nano particles enables control over quantum properties in the XY plane [24], whereas the epitaxial growth controls the Z direction. This approach provides many opportunities and may open the way for developing new photon counting devices. The response spectrum can be tuned by changing the size, shape, or composition of the NCs. The high sensitivity is achieved by obtaining a large gain for the on state. The organic molecules’ couplers were chosen to act mainly as a tunnel barrier between the excited state in the NCs and the device surface states, thus reducing their dependence on the temperature. By optimizing the FET structure to operate at lower temperatures several parameters can be improved such as signal-to-noise ratio (SNR), Johnson noise and mobility, thus improving dramatically the detector's performance.

The schematics of our experimental device are shown in Fig. 1a. Self-assembled monolayers (SAMs) are used for linking the NCs to the solid-state device. In this specific case, colloidal InAs NCs were covalently adsorbed on a SAM that linked them to the surface of a 2DEG GaAs/AlGaAs field effect transistor. The device is then illuminated by a laser with energies smaller than the GaAs energy band gap and larger than the InAs energy gap (Fig. 1c). Under illumination, the photo-excited holes are transferred to the transistor surface states via the SAM. The induced change in the surface potential bends the surface energy levels, thereby increasing the 2DEG electron's density. Therefore, by measuring the enhanced conductivity of the transistor channel (Fig. 1b), sub GaAs band-gap illumination can be detected [18], [19]. In all the devices used here, the above mechanism was confirmed by measuring a positive jump in the DC response under light illumination, a jump that was absent without the NCs.

The change in the FET current can be larger by several orders of magnitude than the number of electrons photoexcited in the NCs. This results from the intrinsic gain mechanism underlying the transistor. In most devices the large possible gain does not greatly improve the signal-to-noise ratio. The small difference created in the gate voltage, when photons are absorbed, does not significantly change the gain of the on or off states. This is not true, however, if the channel can be opened or closed by a single event. By narrowing the channel the sensitivity increases and the signal-to-noise ratio can improve. Controlled reduction in the transistor conducting channel can be achieved using etching and a side gate. By approaching the 1D conduction limit in the sub threshold regime, a small surface dipole field is enough to induce large conductivity, which, consequently, can dramatically change the gain. At the 1D limit, where only one conducting channel is available one loses the possibility of counting the photons and consequently and the detector's noise increases for high photon flux.

Section snippets

Materials and methods

The InAs nanocrystals were linked to the GaAs substrate using HS–(CH2)9–SH [1,9-nonane-dithiol (DT)] molecules. Samples were prepared in three steps: First, the GaAs were sonicated in acetone and ethanol solutions for 2 min each. Then the GaAs were etched for 5 s with 2% HF, washed with double-distilled water (DDW), etched with NH4OH for 30 s, and finally washed with DDW. In the second step the substrates were soaked in absolute ethanol for 20 min before they were immersed into a 1 mM ethanol

Results and discussion

In a previous study we showed that the addition of adsorption layers, that increases the NC density on top of the detector, enhances the device's response [19]. In this work we optimized the detector contacts and channel width to achieve higher sensitivity. The response of the detector was measured for a wide range of light intensities spanning from 10−11 W/cm2 to 10−5 W/cm2. The measurements were taken under a constant current of 0.23 mA using a 980 nm wavelength laser. Fig. 3 displays the light

Conclusions

In conclusion, the electronic and photoresponsive properties of a hybrid organic NC detector were studied at room temperature and presented fast (∼10 ms) and highly sensitive response. Owing to the narrow HEMT channel, the photosensitive device exhibits a very high photoresponsivity of 106 V/W. The signal-to-noise ratio enables high sensitivity to very low photon powers. Noise measurements show that the detector's noise equivalent power can be further improved by two orders of magnitude.

Acknowledgment

Special thanks to Dr. Irene Dujovne for her major contribution and for fruitful discussions.

A. Neubauer received his master's degree in applied physics in 2012 from the Hebrew University of Jerusalem, Israel. Currently he is working on his Ph.D. on Room temperature single photon infrared hybrid organic-nanocrystal detectors in the Hebrew University of Jerusalem.

References (33)

  • J.C. Zolper

    A review of junction field effect transistors for high-temperature and high-power electronics

    Solid-State Electron.

    (1998)
  • S.M. Sze et al.

    Resistivity, mobility and impurity levels in GaAs, Ge, and Si at 300 °K

    Solid-State Electron.

    (1968)
  • W.R. Curtice

    A MESFET model for use in the design of GaAs integrated circuits

    IEEE Trans. Microw. Theory Tech.

    (1980)
  • B. Kolner et al.

    Electrooptic sampling in GaAs integrated circuits

    IEEE J. Quantum Electron.

    (1986)
  • H.J. Yeh et al.

    Fluidic self-assembly for the integration of GaAs light-emitting diodes on Si substrates

    IEEE Photonics Technol. Lett.

    (1994)
  • N.E.J. Hunt et al.

    Increased fiber communications bandwidth from a resonant cavity light emitting diode emitting at λ = 940 nm

    Appl. Phys. Lett.

    (1993)
  • S. Adachi

    Properties of Aluminium Gallium Arsenide

    (1993)
  • Z.L. Yuan et al.

    High speed single photon detection in the near infrared

    Appl. Phys. Lett.

    (2007)
  • J.F. Dynes et al.

    A high speed, postprocessing free, quantum random number generator

    Appl. Phys. Lett.

    (2008)
  • A. McCarthy et al.

    Long-range time-of-flight scanning sensor based on high-speed time-correlated single-photon counting

    Appl. Opt.

    (2009)
  • F. Liu et al.

    High-sensitivity photodetectors based on multilayer GaTe flakes

    ACS Nano

    (2014)
  • O. Lopez-Sanchez et al.

    Ultrasensitive photodetectors based on monolayer MoS2

    Nat. Nanotechnol.

    (2013)
  • N. Perea-López et al.

    Photosensor device based on few-layered WS2 films

    Adv. Funct. Mater.

    (2013)
  • D. Sun et al.

    Ultrafast hot-carrier-dominated photocurrent in graphene

    Nat. Nanotechnol.

    (2012)
  • H. Chang et al.

    Regulating infrared photoresponses in reduced graphene oxide phototransistors by defect and atomic structure control

    ACS Nano

    (2013)
  • B.E. Kardynał et al.

    An avalanche-photodiode-based photon-number-resolving detector

    Nat. Photonics

    (2008)
  • Cited by (8)

    View all citing articles on Scopus

    A. Neubauer received his master's degree in applied physics in 2012 from the Hebrew University of Jerusalem, Israel. Currently he is working on his Ph.D. on Room temperature single photon infrared hybrid organic-nanocrystal detectors in the Hebrew University of Jerusalem.

    S. Yochelis graduated her Ph.D. in 2006, on formation mechanisms of chemical bath deposited semiconductor nanocrystals, at the Weizmann Institute of Science, Israel. Then studied the preparation of hydrogen detectors based on changes in Tungsten absorption spectra embedded in sol–gels at Innosense LLC., Torrance, California. Nowadays, she is a research associate, investigating hybrid self-assembled organic molecules onto inorganic surfaces at the Hebrew University of Jerusalem, Israel.

    Y. Amit holds a M.Sc. in chemistry, specializing in nanoscience and nanotechnology, from the Hebrew University of Jerusalem (2011). Currently he is a Ph.D. candidate at the Hebrew University of Jerusalem conducting my research on the synthesis, characterization of heavily doped colloidal semiconductor nanocrystals and their subsequent implementation in advanced optoelectronic devices.

    U. Banin is a full professor and holds the Alfred & Erica Larisch Memorial Chair in Solar Energy at the Institute of Chemistry at the Hebrew University of Jerusalem (HU). Dr. Banin was the founding director of the Center for Nanoscience and Nanotechnology (2001–2010). He received his Ph.D. degree in Physical Chemistry from HU in 1994 working on femtochemistry (Cum Laude), and was postdoc at the University of California at Berkeley with Professor Paul Alivisatos, studying the chemistry and physics of semiconductor nanocrystals. Dr. Banin joined the faculty of the Institute of Chemistry at HU in 1997and became full professor in 2005. He led the HU program in the frame of the Israel National Nanotechnology Initiative (2007–2010). Banin also serves on HU Executive Committee and on its board of managers. He served on the scientific advisory board of Nanosys. In 2009 Banin was the scientific founder of Qlight Nanotech developing the use of nanocrystals in display and lighting applications. His distinctions include the Rothschild and Fulbright postdoctoral fellowships (1994–1995), the Alon fellowship for young faculty (1997–2000), the Yoram Ben-Porat prize (2000), the Israel Chemical Society prize for a young scientist (2001), and the Michael Bruno Memorial Award (2007–2010).

    Y. Paltiel is an Associate Professor at The Hebrew University of Jerusalem and the chair of the Applied Physics Department. He received his M.Sc. and Ph.D. degrees at the Physics Department at the Weizmann Institute. At 2002 he joined a start-up company as the head of a quantum devices group, followed by working at the Solid State Physics group at Soreq NRC, with a tenure position from 2006. In 2008, during a sabbatical he was one of the core founders of a new startup company. Since July 2009, Yossi has been leading the Applied Physics Department Quantum Nano Engineering group at the Hebrew University.

    View full text