Elsevier

Solid State Communications

Volume 270, February 2018, Pages 135-139
Solid State Communications

Fast-track communication
Gate-tunable transport characteristics of Bi2S3 nanowire transistors

https://doi.org/10.1016/j.ssc.2017.12.005Get rights and content

Highlights

  • Electrical characterization of Bi2S3 nanowire transistors over a wide range of temperature and drain-source bias.

  • Charge Carrier mobility, ON/OFF ratio and activation energy are analyzed.

  • Resistance noise spectroscopy supports evidence of mid-gap states in the system.

  • Findings support the impact native sulfur vacancies have on band structure of sulfide nanostructures.

  • Findings are beneficial for understanding nanoscale chalcogenide systems.

Abstract

Electrical transport and resistance noise spectroscopy measurements are performed on individual, single crystalline Bi2S3 nanowires in the field-effect geometry. The nanowires exhibit n-type conduction and device characteristics such as activation energy, ON/OFF ratio, and mobility are calculated over a temperature range of 120–320 K and at several bias values. The noise magnitude is measured between 0.01 and 5 Hz at several gate voltages as the device turns from it's OFF to ON state. The presence of mid-gap states which act as charge traps within the band gap can potentially explain the observed transport characteristics. Sulfur vacancies are the likely origin of these mid-gap states which makes Bi2S3 nanowires appealing for defect engineering as a means to enhance its optoelectronic properties and also to better understand the important role of defects in nanoscale semiconductors.

Introduction

Semiconducting nanowire field effect transistors (NWFETs) have been a staple of research in low dimensional electronics for the efforts of finding a suitable means of scaling down current technology [[1], [2], [3]]. Nanowires have been envisioned to fulfill roles in thermoelectrics [4,5], optoelectronics [6,7], and as various sensors [8,9]. Nanowires are advantageous for these technologies because of their superior properties compared to planar films; since nanowires have exhibited lower noise intensity [10], better electrostatic control [11] and drastically lower thermal conductivity due to phonon confinement which is beneficial for thermoelectrics [12]. For optoelectronics, it has been shown that the light trapping properties of nanowires make them more efficient than thin films [13]. Also, incorporating III - V materials with existing silicon technology has been an ongoing challenge due to lattice mismatch, but nanowires have changed that with epitaxial growth on silicon [14]. However, the high surface area-to-volume ratio of semiconducting nanowires means that they are at constant risk of having surface defects which significantly hinder their mobility compared to their bulk counterparts [15,16]. In addition, the growth of these nanowires followed by the fabrication of devices with parameters such as annealing time and choice of contact metals have a dramatic impact on the performance of these devices [17]. Hence, understanding defect behavior that often plague device performances are a necessity.

Layered semiconducting chalcogenides, especially bismuth chalcogenides, are a family of materials that have been drawing increased attention as low dimensional structures due to their vast array of interesting physical properties. Two prominent members, bismuth selenide, Bi2Se3 and bismuth telluride, Bi2Te3 are topological insulators [[18], [19], [20]], and are already established as good thermoelectric materials [21]. However, Bi2S3 lacks the toxicity of those two materials and the fact that sulfur vacancies could be potentially tuned in this material makes it worthy of exploring for electronic, thermoelectric and optical applications. Bi2S3, a prominent family member with an orthorhombic crystal structure, has many diverse and useful qualities such as a small band gap of 1.3–1.7 eV [22,23], high bulk mobility [24], high Seebeck coefficient [25], and low thermal conductivity [24,25]. Due to these distinct physical properties, Bi2S3 has been incorporated as the active material in optical [26,27], electronic [28,29] and thermoelectric technologies [30].

Additionally, transition-metal sulfides are attractive candidates for defect engineering of sulfur vacancies. Sulfur vacancies can impact the band structure of a material and thereby alter the electronic and optical properties [31]. For example, the formation of mid-gap states from these defects has been seen in other sulfide materials such as in MoS2 and WS2 [32,33] and has been attributed to the low luminescence quantum yield. The vacancies have also been shown to act as adsorption sites for gases which can lead to modulated electronic performance in the form of increased or decreased conductivity and field effect mobility depending on the specific gas [34]. Recently, calculations have shown that native sulfur vacancies can likewise produce mid-gap states in the Bi2S3 band structure which act as charge traps [[35], [36], [37]]. In previous works, it was experimentally shown that Bi2S3 optoelectronic devices had their performance and quantum yield hindered by what qualitatively seemed to be charge trapping which affects electron and hole recombination [38,39]. The impact of this altered band structure on the transport properties for the most fundamental building block of electronics, the transistor, have not been realized. In this work we show a systematic study of the transport characteristics in Bi2S3 nanowire transistors and present supporting evidence for the mid-gap states induced from vacancies. Specifically, we characterized the charge transport properties of Bi2S3 nanowires over a wide temperature range and developed a deeper understanding of the charge transport mechanisms in Bi2S3 single nanowire field effect transistors via transport and noise spectroscopy studies. Noise spectroscopy is a method to probe the intrinsic fluctuations of a system to obtain an understanding of the microscopic conduction mechanisms, which normally cannot be obtained through standard transport characterization [40]. Our current work sets the stage for many new works to be explored, from deeper noise spectroscopy studies to defect engineering to tune these vacancies and the electronic properties of Bi2S3 for future applications.

Section snippets

Nanowire growth & device fabrication

The Bi2S3 nanowires with a mean diameter of 36 nm were synthesized through a hydrothermal method, the details of which can be found elsewhere [41]. The orthorhombic structure is depicted in Fig. 1 (A). Bi2S3 possesses a highly anisotropic lamellar crystal structure that consists of ribbon-like [Bi4S6] cages linked together by the intermolecular interaction between Bi and S atoms. These ribbon-like [Bi4S6] cages, which are oriented parallel to the c-axis, dictate the growth direction in Bi2S3

Transistor characterization

Transistor characteristics were studied at several drains-source biases as well as at several temperatures. All nanowires show n-type conduction which has been previously attributed to sulfur vacancies in other Bi2S3 works [44]. Other n-type sulfide materials such as MoS2 have shown the same origin for their n-type conductance [45]. Gate voltage sweeps at various temperatures are shown in Fig. 2 (C). As the temperature is increased, the threshold voltage to turn the device ON decreases and the

Conclusion

In conclusion, Bi2S3 nanowire back gated field effect transistors have been characterized and their transistor parameters such as, mobility and ON/OFF were studied. Mobility is shown to be dependent on both electron-lattice scattering as well as defect/impurity scattering as temperature and drain-source bias are modified. The overall values range from 0.041 to 2.58 cm2/V s. The ON/OFF ratio ranged from 2 to 5 orders which at room temperature became roughly bias independent due to a large

References (57)

  • X. Chen et al.

    Sens Actuators B Chem

    (2013)
  • F. Patolsky et al.

    Mater. Today

    (2005)
  • Y.L. Chen et al.

    Science

    (2009)
  • J.D. Desai et al.

    Mater. Chem. Phys.

    (1995)
  • Y. Xi et al.

    Solid State Commun.

    (2009)
  • Y. Yu et al.

    Mater. Lett.

    (2009)
  • Y. Cui et al.

    Science

    (2001)
  • P.S. Peercy

    Nature

    (2000)
  • J. Appenzeller et al.

    IEEE Trans. Electron. Dev.

    (2008)
  • J. Kim et al.

    J. Mater. Chem. C

    (2015)
  • A.I. Boukai et al.

    Nature

    (2008)
  • L. Cao et al.

    Nat. Mater.

    (2009)
  • L. Vj et al.

    IEEE J. Sel. Top. Quant. Electron.

    (2011)
  • W. Feng et al.

    Jpn. J. Appl. Phys.

    (2012)
  • Z. He et al.

    J. Phys. Chem. C

    (2010)
  • I. Ponomareva et al.

    Nano Lett.

    (2007)
  • E. Garnett et al.

    Nano Lett.

    (2010)
  • Thomas Martensson et al.

    Nano Lett.

    (2004)
  • H.J. Joyce et al.

    Nano Lett.

    (2012)
  • A.C. Ford et al.

    Nano Lett.

    (2009)
  • D. Ovchinnikov et al.

    ACS Nano

    (2014)
  • D. Hsieh et al.

    Nature

    (2008)
  • Y. Xia et al.

    Nat. Phys.

    (2009)
  • S.K. Mishra et al.

    J. Phys. Condens. Matter

    (1997)
  • C. Ye et al.

    J. Am. Chem. Soc.

    (2002)
  • Z.-H. Ge et al.

    J. Mater. Chem.

    (2011)
  • Z.-H. Ge et al.

    J. Mater. Chem.

    (2012)
  • L. Whittaker-Brooks et al.

    J. Mater. Chem. C

    (2015)
  • View full text