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High-Speed III-Nitride Visible LEDs

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Visible light communication (VLC) is considered to be one of the best candidates to meet future demand in ultra-broadband indoor wireless access networks. An indoor optical wireless acttocell network can be realized by installing a large number of white-light light-emitting diode (LED) lamps on the ceiling of a building to act as transmitters. One of the major factors limiting the bandwidth in the VLC system has been the direct modulation speed of the visible LEDs inside the lamps. Another promising application for high-speed visible LEDs operating at the red or cyan wavelengths would be in polymethylmethacrylate (PMMA) based plastic optical fiber (POF) communication systems. Although the red vertical-cavity surface-emitting laser (VCSEL) technology has been demonstrated to work at a much faster speed than that of the red and green (or cyan) LEDs (RCLEDs), an LED based solution would have a much lower cost and be advantageous for harsh-environment communication, such as for in-car data transmission, due to the much lower required driving current density than that of the VCSEL. This characteristic provides the improved device reliability of high-speed LEDs and makes the development of visible LEDs with a GHz bandwidth under a lower driving current (density) than that of the laser diode (LD) become the key issue. In most cases, the modulation speed of the LED is limited by the spontaneous recombination time in the active layer. The reported maximum 3-dB electrical-to-optical (E-O) bandwidth is usually less than 500 MHz, which corresponds to a carrier recombination time of around 320 ps. It has been demonstrated that this time constant can be further shortened by heavy p+ doping (>1×?10?^19cm-3) of the active layer in GaAs or InP based LEDs, achieving an E-O bandwidth > 1 GHz. However, there is a serious sacrifice of the internal quantum efficiency (output power) arising from the enhancement of the non-radiative recombination process induced by the p-type dopant (defects). Over these years, we continuously have high-impact contribution in the high-speed visible III-nitride LEDs. By improving the MQWs design in GaN based LED, we can simultaneously improve the modulation speed and output power of LED. We achieve a record high 3-dB E-O bandwidth (1 GHz) among all the reported visible LEDs. The speed performance is superior even to that of the GaN based green (~500 nm) laser diodes (LDs) (1 vs. 0.4 GHz).


Figure 1 shows the top-view of demonstrated LED, zoom-in picture of patterned sapphire (PS) substrate, and LED with TO-CAN package.


Figure 2 shows the measured E-O frequency response. As can be seen, when the bias current reaches 90 mA bias, a nearly 1 GHz 3-dB E-O bandwidth can be achieved.


Figure 3 shows the transmission results over POF, we can clearly see that when the transmission distance is less than 20 meter, data rate as high as 3 Gbit/sec can be attained.


Related papers：

1. J.-W. Shi, H.-Y. Huang, J.-K. Sheu, C.-H. Chen, Y.-S. Wu, and W.-C. Lai, “The improvement in Modulation Speed of GaN-Based Light-Emitting Diode (LED) by Use of n-Type Barrier Doping for Plastic Optical Fiber (POF) Communication” IEEE Photon. Technol. Lett., vol. 18, pp. 1636-1638, Aug., 2006.

2. J.-W. Shi, J.-K. Sheu, C.-H. Chen, G.-R. Lin, and W.-C. Lai, “High-Speed GaN-based Green Light Emitting Diodes with Partially n-doped Active Layers and Current-Confined Apertures,” IEEE Electron Device Lett., vol. 29, pp. 158-160, Feb., 2008.

3. J.-W. Shi, P-.Y. Chen, C.-C. Chen, J.-K. Sheu, W.-C. Lai, Yun-Chih Lee, Po-Shen Lee, Shih-Pu Yang, and Mount-Learn Wu, “Linear Cascade GaN Based Green Light Emitting Diodes with Invariant High-Speed/Power Performance under High-Temperature Operation,” IEEE Photon. Technol. Lett., vol. 20, pp. 1896-1898, Dec., 2008.

4. J.-W. Shi, H.-W. Huang, F.-M. Kuo, J.-K. Sheu, W.-C. Lai, M. L. Lee, “Very-High Temperature (200℃) and High-Speed Operation of Cascade GaN Based Green Light Emitting Diodes with an InGaN Insertion Layer,” IEEE Photon. Technol. Lett., vol. 22, pp. 1033-1035, July, 2010.

5. J.-W. Shi, H.-W. Huang, F.-M. Kuo, W.-C. Lai, M. L. Lee, and J.-K. Sheu, “Investigation of the Carrier Dynamic in GaN-Based Cascade Green Light-Emitting-Diodes Using the Very-Fast Electrical-Optical Pump-Probe Technique,” IEEE Trans. on Electron Device. vol. 58, pp. 495-500, Feb., 2011.

6. Jhih-Min Wun, Che-Wei Lin, Wei Chen, J.-K. Sheu, Ching-Liang Lin, Yun-Li Li, John E. Bowers, Jin-Wei Shi, Juri Vinogradov, Roman Kruglov, and Olaf Ziemann, “GaN Based Miniaturized Cyan Light Emitting Diodes on Patterned Sapphire Substrate with Improved Fiber Coupling for Very-High-Speed Plastic Optical Fiber Communication,” IEEE Photonics Journal, vol. 4, No.5, pp. 1520-1529, Oct., 2012.

7. J. Vinogradov, R. Kruglov, K.-L. Chi, J.-W. Shi, M. Bloos, S. Loquai, and O. Ziemann “GaN Light-Emitting Diodes for up to 5.5 Gb/s Short-Reach Data Transmission over SI-POF ” IEEE Photon. Technol. Lett., vol. 26, no. 24, pp. 2473-2475, Dec., 2014.

8. Jin-Wei Shi, Kai-Lun Chi, Jhih-Min Wun, J. E. Bowers, Ya-Hsuan Shih, and Jinn-Kong Sheu, “III-Nitride Based Cyan Light-Emitting Diodes with GHz Bandwidth for High-Speed Visible Light Communication,” IEEE Electron Device Lett., vol. 37, pp. 894-897, July, 2016.

9. J. Vinogradov, R. Kruglov, R. Engelbrecht, O. Ziemann, J.-K. Sheu, K.-L. Chi, J.-M. Wun, and J.-W. Shi, “GaN-Based Cyan Light Emitting Diode with up to 1?GHz Bandwidth for High-Speed Transmission over SI-POF” IEEE Photonics Journal, vol. 9, no. 3, pp. 7201707, June, 2017.