Current-voltage characteristics of iron-implanted silicon based Schottky diodes

https://doi.org/10.1016/j.mssp.2020.105524Get rights and content

Highlights

  • A change inI–V properties of Si diode with Fe fluence implanted in the material has been studied.

  • In silicon Iron is responsible for ohmic (I–V) behaviour of the diodes fabricated on the material.

  • A variation of rectification ration with Iron fluence has been used to explain a conductivity-type inversion of silicon.

  • Properties of Fe-doped Si diode are similar to those of devices that were found resistant to radiation damage.

Abstract

Current-voltage (I–V) measurements were carried out on undoped and iron (Fe) doped n-silicon (n-Si) to establish and study a change in electrical properties of the material-based diodes with Fe doping concentration. Fe doping was achieved by implantation at the energy of 160 keV to fluences of 1015, 1016 and 1017 ion/cm2. The obtained results indicated that the diodes were well fabricated and Fe doping resulted in a diode behaviour changing from normal exponential to ohmic I–V behaviour. This ohmic behaviour was explained in terms of Fe-induced defect levels that were positioned at the centre of the energy gap. An I–V ohmic region increased with fluence indicating that the density of defect levels has increased with Fe implantation fluence. A change in diode conduction mechanism domination and parameters with fluence were investigated. The obtained I–V properties of Fe doped Si-based diodes were similar to those of the diodes that were fabricated on radiation-hard materials indicating that Fe, too, is a promising dopant in a quest to improve radiation-hardness of Si to be used in high energy physics experiments.

Introduction

Crystalline silicon is used for fabrication of radiation detectors in high energy physics experiments due to its unique advantages like moderate energy gap, stability in high temperature and cost-friendly due to its abundance in nature, to mention the few. Detectors that are made from this material, however, gets damaged by the same radiation they intend to detect. The damage results in defect levels in the energy gap of Si that are responsible for a change in the microscopic properties of detectors. It is therefore important that radiation-hardness of Si is improved to make the material suitable for the fabrication of efficient radiation detector to be used in the current and future high energy physics experiments [1].

In trying to improve radiation-hardness of the material, numerous studies have shown that a heavy pre-irradiation [2] oxygenation [3] and doping Si with metals such as gold (Au) and platinum (Pt) [4] are promising methods. In Si, Au and Pt were found to be responsible for relaxation behaviour of the material [5] but they are, however, relatively expensive resulting in very limited research on radiation-hardness of Si. It is, therefore, important that the effects of other metal dopants in Si are established and studied. These dopants should be abundant and have similar behaviour as Au and Pt in Si.

In p-Si, Fe acts as donor impurity consequently reducing the concentration of holes [6], hence, reducing the conductivity of the material. The resistivity of n-Si, on the other hand, has been found to remain unchanged after doping with Fe concentration of 1014 cm−3 [7]. Based on the literature reviewed, the effects of Fe on electrical properties of Si at a concentration higher than 1014 cm−3 have not been studied. In Si, Fe creates defect levels at EV +0.40, EC -0.55 and EC -0.27 eV in the energy gap [8]. The main motive of studying the effects of Fe dopants in Si is due to ~0.55 eV defect level, which was found to be induced by Au and Pt [9,10]. A defect level at ~0.56 eV in the energy gap is responsible for relaxation behaviour of Si [11]. Devices fabricated on relaxation material show ohmic I–V behaviour [5,11] and they have been proven to be resistant to radiation damage [12]. These devices, however, have high leakage current showing that their radiation detection sensitivity is low. This shortfall encourages a search of the most suitable dopant to improve Si properties for radiation detection applications.

In this work, diodes were characterized using I–V technique to investigate the effects of Fe doping on the electrical properties of Si-based devices. The results indicate, for the first time, that in Si, Fe exhibits similar properties as other metals (Au and Pt) that have been found promising to improve radiation-hardness of Si. Hence, Fe could be a suitable replacement in case these two metals are disqualified due to their unavailability and scarcity.

Section snippets

Material preparation

In this study, an n-Si wafer polished on one side was diced into 0.9 cm × 0.9 cm square substrates. The resistivity of the material was quoted ranging from 1 to 20 Ω-cm with a thickness of 275 ± 25.0 μm. The standard cleaning procedure using methanol, acetone, trichloroethane and de-ionized water was used [5,13] to remove any handling grease and residue. An oxide layer was removed by dipping the substrates into 40% hydrofluoric (HF) solution. The substrates were then blow-dried using nitrogen

Results and discussion

The I–V trends for each diode in this work are represented in different scales to investigate the quality of the fabricated device and to study a variation of device current trends as a function of Fe fluence implanted in Si. Fig. 2(a) shows I–V characteristics of the unimplanted n-Si-based diode in a linear-linear scale. As expected, the current is completely independent of voltage in this scale since the reverse current is due to minority carriers (holes) in n-Si. In forward bias, the current

Conclusion

In this work, Schottky diodes were well fabricated on undoped and Fe-implanted n-Si. The diodes were characterized using the I–V technique. Diodes that were fabricated on Fe-implanted n-Si show ohmic I–V behaviour. This ohmic behaviour indicated that in Si, Fe induce g-r centres, defect levels positioned at the centre of the energy gap. The observed increase in ohmic region indicated that the induced g-r centres increased with fluence. In addition, the obtained results indicated that in Si, Fe

Author statement

J. O. Bodunrin: student investigator, data analysis, original draft preparation.

D. A. Oeba: editing.

S. J. Moloi: supervision, conceptualization, methodology, writing-reviewing and editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The first author acknowledges the National Research Foundation (NRF) and The World Academy of Science (TWAS) for student funding (Grant number 116113). This work is based on the research supported wholly by the National Research Foundation of South Africa (Grant numbers 105292 and 114800). We would like to thank Mr. Tony Miller of iThemba LABS for Iron implantation.

References (37)

  • G. Kramberger

    Nucl. Instrum. Methods A

    (2019)
  • P.G. Litovchenko et al.

    Nucl. Instrum. Methods A

    (2006)
  • L. Fonseca

    Microelectron. Reliab.

    (2000)
  • S.J. Moloi et al.

    Physica B: Phys. Condens. Matter

    (2009)
  • S.J. Moloi et al.

    Physica B: Phys. Condens. Matter

    (2009)
  • S. Mahato et al.

    Physica B: Phys. Condens. Matter

    (2018)
  • M. Siad et al.

    Appl. Surf. Sci.

    (2004)
  • O. Gullu et al.

    Microelectron. Eng.

    (2008)
  • S. Aydogan et al.

    Mater. Sci. Semicond. Process.

    (2008)
  • M. Msimanga et al.

    Radiat. Phys. Chem.

    (2004)
  • V.N. Brudnyi et al.

    Physica B: Phys. Condens. Matter

    (1995)
  • M.J. Parida et al.

    Nucl. Instrum. Methods A

    (2018)
  • L. Agarwal et al.

    Thim Solid Films

    (2016)
  • I.M. Afandiyeva et al.

    J. Alloys Compd.

    (2013)
  • D. Pitzl et al.

    Nucl. Instrum. Methods A

    (1992)
  • S. Aydogan et al.

    Microelectron. Eng.

    (2008)
  • H. Altuntaş et al.

    Microelectron. Reliab.

    (2009)
  • S. Mohammad et al.

    Prog. Quant. Electron.

    (1996)
  • Cited by (10)

    View all citing articles on Scopus
    View full text