Light emitting diode structure based on Si nanocrystals formed by implantation into thermal oxide

doi:10.1016/S0022-2313(98)00109-4

Journal of Luminescence

Volume 80, Issues 1–4, December 1998, Pages 263-267

https://doi.org/10.1016/S0022-2313(98)00109-4 Get rights and content

Abstract

Light emitting diodes (LED), continuously operable at room temperature, have been fabricated by Si⁺ ion implantation into SiO₂ and subsequent annealing in order to form Si nanocrystals. A highly doped poly-Si layer was used to enhance injection into nanocrystals. Visible electroluminescence (EL) was observed from the LEDs with oxide thickness ⩽180 Å for bias voltages above 8 V. The EL decay transient was similar to stretched-exponential decays observed for photoluminescence (PL) from Si nanocrystals.

Introduction

Although porous silicon exhibits strong, visible photoluminescence [1], fabrication of light emitting diodes has been far less successful. While a rather high efficiency has been achieved 2, 3, 4, the stability is still a problem. An alternative system is Si nanocrystals, formed by Si⁺ ion implantation into SiO₂ 5, 6, 7, 8, 9. Those structures are stable and fully compatible with VLSI processing technology. However, for EL applications, inefficient carrier injection through the oxide is an obstacle. The purpose of this work was to investigate the possibility of manufacturing light emitting diodes from Si nanocrystals, with a stable EL in air ambient and operable at low voltages. To improve carrier injection, thin oxide layers were needed, as well as a highly doped injection layer. The diodes, manufactured by Si⁺ ion implantation into SiO₂, exhibited visible continuous EL at room temperature. Here we present the results of electrical and optical characterization of the diodes.

Section snippets

Experimental

Samples were prepared from p-type Si (1 0 0) wafers of resistivity 20 Ω cm. First, thermal oxides with thicknesses of 120, 180, 500 and 1000 Å were grown, followed by a deposition of a 2100 Å thick amorphous Si layer with dual purpose: to adjust the position of the implantation profile peak and to serve as a contacting and protective layer to the SiO_x layer. This structure was implanted with $^{28} Si^{+}$ ions at an energy of 150 keV to doses of 3×10¹⁶, 1×10¹⁷ and 3×10¹⁷ cm⁻², and annealed in N₂ atmosphere at

Results and discussion

The room-temperature EL from a diode with a 180 Å oxide thickness, implanted to 3×10¹⁷ cm⁻², and operated under a continuous forward bias of 16 V is shown in the inset in Fig. 2, as recorded with a CCD camera. The EL intensity was homogeneously distributed over the diode area. EL was also observed under reverse bias, but it was more than an order of magnitude weaker. The EL spectra are shown in Fig. 2, along with a PL spectrum for comparison. The PL spectrum was measured in the oxide area between

Summary

A VLSI compatible process for the fabrication of LED based on Si nanocrystals has been evaluated. Visible EL at low voltages has been observed from the diodes with a thin oxide layer, showing that it is possible to achieve efficient injection through a thin oxide. The EL was stable, due to a good passivation of the Si nanocrystals embedded in the oxide. The EL decay was similar to stretched-exponential decays reported for the PL. Shorter time constants for higher implantation doses are

Acknowledgements

NL is holder of a grant from the EIT faculty of the Royal Institute of Technology. The authors are also grateful to T. Pihl for ion implantation.

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Light emitting diode structure based on Si nanocrystals formed by implantation into thermal oxide

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Summary

Acknowledgements

Thin Solid Films

Phys. Rev. B

Appl. Phys. Lett.

Electron. Lett.

Appl. Phys. Lett.

J. Phys.Condens. Matter

Mat. Res. Soc. Symp. Proc.

Phys. Rev. B