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# Transparent electrodes based on GaAs/metal subwavelength gratings for VCSEL applications

Natan Monvoisin, Weronika Glowadzka, Franck Carcenac, Aurélie Lecestre, Benjamin Reig, Stéphane Calvez, Antoine Monmayrant, Olivier Gauthier-Lafaye, Tomasz Czyszanowski, Guilhem Almuneau

► To cite this version:

Natan Monvoisin, Weronika Glowadzka, Franck Carcenac, Aurélie Lecestre, Benjamin Reig, et al. Transparent electrodes based on GaAs/metal subwavelength gratings for VCSEL applications. VCSEL Day 2023, Sep 2023, Turin (IT), Italy. 2023. [hal-04768581](https://hal-04768581)

HAL Id: hal-04768581

https://laas.hal.science/hal-04768581v1

Submitted on 12 Nov 2024

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# Transparent electrodes based on GaAs/metal subwavelength gratings for VCSEL applications

N. Monvoisin¹, W. Glowadzka², F. Carcenac¹, A. Lecestre¹, B. Reig¹, S. Calvez¹, A. Monmayrant¹, O. Gauthier-Lafaye¹, T. Czyszanowski², G. Almuneau¹

1: LAAS-CNRS, France, 2: Łódź University of Technology, Poland

## Context

* Standard oxide-confined VCSEL with annular top-electrode geometry leads to poor injection uniformity

* Strong interest for **efficient uniform electrical injection** whatever the emission window diameter and shape

* Need for a **transparent electrode** scalable in size with **high transparency** with fixed **light polarization** and **good electrical conductivity**

* Transparent conductive electrodes (TCE) already proposed/used on VCSEL: Indium Tin Oxide (ITO), silver nanostructured materials and graphene films

=> Limitations of electrical performances (compared to metal electrodes) and scarcity of In resources.

<figure><img src="image_2.png" /></figure>

* **Optical transparency** as nearest as possible to 100%

* **Electrical resistance** as low as 1 Ω/□

* Scalable to device size/geometry

* Compatible with standard VCSEL fabrication process

<figure><img src="image_3.png" /></figure>

## Methods

* Semiconductor-metal deep-subwavelength grating (SMDSG)

* New TCE concept proposed by Technical Univ. Lodz [1]

* Demonstrations in mid-infrared spectral window [2]

* This work is the **first experimental demonstration** of SMDSG in **near-infrared range** and on **GaAs** platform

[1] T. Czyszanowski, Adam K. Sokóa, et al. Optics Express 28.19 (Sept. 2020), p. 28383.

[2] L.Y.M. Tobing, Michaal Wasiak, et al. Nanophotonics 10.15 (Nov. 2021), pp. 38233830.

## Design and nanofabrication

### « Bottom » configuration (TE polarization)

<figure><img src="image_4.png" /></figure>

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<figure><img src="image_8.png" /></figure>

### «Top » configuration (TM polarization)

<figure><img src="image_9.png" /></figure>

<table><thead><tr><th>Structure</th><th></th><th>Λ (nm)</th><th>F</th><th>H (nm)</th><th>H<sub>Au</sub> (nm)</th><th>H<sub>Ti</sub> (nm)</th><th>Transmission</th></tr></thead><tbody><tr><td rowspan="2">B-TE-TiAu-1</td><td>Theory</td><td>180</td><td>0.6</td><td>85</td><td>50</td><td>5</td><td>92 % (TE)</td></tr><tr><td>Measured</td><td>180</td><td>0.53±0.01</td><td>89±6</td><td>33±5</td><td>5±1</td><td>82 % (TE)</td></tr><tr><td rowspan="2">T-TM-TiAu</td><td>Theory</td><td>100</td><td>0.5</td><td>80</td><td>50</td><td>5</td><td>83 % (TM)</td></tr><tr><td>Measured</td><td>100</td><td>0.57±0.01</td><td>88±6</td><td>27±4</td><td>5±1</td><td>81 % (TM)</td></tr></tbody></table>

* Two configurations for TE and TM light polarization transmission

* Optical impedance matching with no impact on electrical properties

* Grating period : Λ = 0,15-0,25 * λ

* Self-aligned process based on e-beam lithography

* Technological bottlenecks: 50-nm-wide metal line lift-off and controlled ICP etch depth

## Optical and electrical characterizations

<figure><img src="image_10.png" /><figcaption>Experimental spectroscopy measurements of polarized transmission and reflection of fabricated SMDSG</figcaption></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

<table><caption>Schematic of the two-probes measurement of nanowire set resistance</caption><tr><td>TE transmission</td><td>GaAs/air Fresnel transmission</td></tr><tr><td>TM transmission</td><td>GaAs/air Fresnel transmission</td></tr><tr><td>TE reflection</td><td>GaAs/air Fresnel reflection</td></tr><tr><td>TM reflection</td><td>GaAs/air Fresnel reflection</td></tr></table>

<figure><img src="image_14.png" /><figcaption>AFM and SEM images of nanowires and sheet resistance measurements as function of the number of lines</figcaption></figure>

<figure><img src="image_15.png" /></figure>

## Acknowledgments:

* RENATECH (French Network of Technology Platforms) at LAAS-CNRS

* Project TRAVEL funded by an M-ERA.NET grant from the Agence National de la Recherche (ANR-20-MERA-0002)