Elsevier

Journal of Luminescence

Volume 237, September 2021, 118136
Journal of Luminescence

Radiation effects of heavy ions on the static and dynamic characteristics of 850 nm high-speed vertical cavity surface emitting lasers

https://doi.org/10.1016/j.jlumin.2021.118136Get rights and content

Highlights

  • VCSELs are sensitive to radiation damage induced by heavy ions.

  • Enhanced optical absorption leads to degradation of static characteristics.

  • Appropriate ion fluence irradiation can improve the modulation bandwidth.

  • Irradiation damages distributed-Bragg reflectors and quantum wells of VCSEL.

Abstract

We investigate the radiation effects of 1907 MeV Ta ions on the static and dynamic characteristics of 850 nm high-speed vertical cavity surface emitting lasers (VCSELs). The threshold current and slope efficiency are found to be degraded. However, appropriate ion fluence irradiation can improve the modulation bandwidth. The maximum 3 dB frequency is increased to 14.02 GHz from 13 GHz at a fluence of 1 × 108 ions/cm2. The observed behaviour can be explained in terms of reflectivity degradation of lossy distributed-Bragg reflectors as well as the degradation of quantum wells.

Introduction

High speed vertical cavity surface emitting lasers (VCSELs ) have become the preferred light source for short distance transmission links due to their excellent characteristics, such as low threshold current, high-speed modulation, and good beam quality etc. [[1], [2], [3]]. At present, they are widely used in optical interconnects in harsh environments such as avionics, space, and high energy physics [[4], [5], [6]]. In addition, taking their advantages of both low divergence and low linewidth, VCSELs are promising candidates for optical links used in Earth-Satellites and Circular Electron-Positron Collider-Super Proton-Proton Collider (CEPC-SPPC) [5,6]. However, the VCSELs performance can be affected by high fluence particles with high energy in space and CEPC-SPPC [5,7,8]. Therefore, it is imperative to investigate the effect of various high-energy particles such as protons, neutrons and heavy ions on the reliabiity of high-speed VCSELs.

At present, extensive work has been devoted to evaluating radiation damage affecting the static characteristics of devices under various particles irradiation such as protons, neutrons, pions and ions [[9], [10], [11], [12], [13]]. A. Kalavagunta et al. illustrated that the threshold current and output power were degraded under proton irradiation caused by displacement damage effect [[9], [10], [11]], while the slope efficiency was almost unchanged [11]. J. Troska et al. pointed out that VCSELs are more radiation resistant than edge-emitting lasers and pions induce more damage than neutrons [9,12]. N. Venet et al. suggested that no irradiation damage occurs when heavy ion radiation fluence below 1 × 107 ions/cm2 [13]. However, the fluence level of heavy ion can be much higher in practical application, as for example the CEPC-SPPC will collide heavy ions with a fluence as high as 1010 ions/cm2 when it reachs its design performane [5]. In addition, only a few studies of dynamic properties of irradiated VCSELs have been carried out and the underlying mechanisms responsible for the radiation damage are yet to be fully understood. In order to analyze and improve the design of functional devices, a through understanding of radiation effects on irradiated VCSELs with high energy heavy ions is necessary.

In this paper, we examine for the first time the effect of 1907 MeV Ta ion on high-speed oxide-confined VCSEL. The static and dynamic characteristics of devices experienced ion fluences between 5 × 107–1 × 1010 ions/cm2 were investigated. The experimental results show that VCSELs are sensitive to radiation damage induced by heavy ions. The degradation of static characteristics can be attributed to enhanced carrier loss and optical absorption in both cavity and distributed-Bragg reflectors (DBRs). The unusual behavior of dynamic response can be explained in terms of degradation of both DBRs and active region.

Section snippets

Material and methods

The structure of the VCSELs investigated in this study is shown in Fig. 1. The VCSEL is designed for 850 nm operation with a 1.5-λ separate confinement heterostructure (SCH) region containing an active region with three 7 nm thick GaAs quantum wells (QWs) separated by 8 nm Al0.3Ga0.7As barriers. The SCH is sandwiched between a p-doped DBR containing 22 pairs of Al0.9Ga0.1As/Al0.12Ga0.88As and an n-doped DBR containing 34 pairs of Al0.9Ga0.1As/Al0.12Ga0.88As. One 30 nm thick Al0.98Ga0.02As layer

Static performance characteristics of VCSELs

In order to determine the irradiation effects on the device performance, the VCSELs with similar L-I-V and spectral characteristics as shown in Fig. 2 have been selected for followed radiation measurements to exclude wrong information induced by scattered device performance. The typical L-I-V characteristics of irradiated VCSELs are shown in Fig. 3 together with a pre-irradiated L-I-V curve for comparision. The important parameters of device performance including the threshold current Ith,

Conclusion

In conclusion, the radiation effects of 1907 MeV Ta ion on the static and dynamic characteristics of 850 nm VCSELs have been systemically investigated and corresponding mechanisms have been revealed. Our results clearly show that Ta ion radiation induces excessive defects resulting in enhanced carrier loss and optical absorption in both cavity and DBR mirrors. As a result, the static performance characteristics of devices after radiation including threshold current, output power and thermal

Funding

This work was supported by the National Natural Science Foundation of China, (Grants 61804175 and 61874135), Key Research Program of Frontier Sciences, Chinese Academy of Sciences, (No. ZDBS-LY-JSC031 & ZDBS-LY-JSC015), Innovation Center of Radiation Application Project, China Institute of Atomic Energy, (No. KFZC2018040203), Institute of Modern Physics Project, Chinese Academy of Sciences, (No. HIR19PY015).

Author statement

All authors have seen and approved the final version of the manuscript being submitted. We warrant that the article is the authors' original work, hasn't received prior publication and isn't under consideration for publication elsewhere.

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.

Acknowledgements

We thank the members of the HIRFL Accelerator at the Institute of Modern Physics, Chinese Academy of Sciences, for the sample irradiation.

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