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Current Status of DUV Laser


By
Ronghui Lin

December 26, 2016 - Posted in Discussion
Current Status of DUV Laser

To date, the development of DUV laser diode is still at its early stage. DUV laser diodes are still in the lab, far from mass production. Most of these attempts make use of the AlGaN/AlN material system, which is one of the promising material systems that can be used to produce DUV laser with high performance. There are generally three methods to pump the laser diode:

1.      Optical pumping: Optical pumping is the most straightforward way to get a DUV laser. UV laser diode emitting at sub 250 nm region has been demonstrated by the Xiaohang Li1, 2 and a few other groups from around the world3-5. But generating laser light using this method typically require another power with higher optical power and shorter wavelength, which renders this technique impractical for actual applications.

2.      Electrical pumping: Electrically pumped DUV laser diode is the ideal choice. They have been demonstrated at the longer emission wavelength, such as 342 nm6, 275 nm7, 330 nm8. The challenges for achieving electrically injected deep UV using AlGaN quantum well include the presence of large numbers of dislocation densities, large polarization fields, and inefficient p- and n-type doping for AlGaN with high Al fraction.  These factors hamper the EQE and the output power of electrically injected AlGaN MQW DUV lasers. Some researchers turn their eyes to nanowires because high crystal quality, high light extraction efficiency and low strain induced polarization can be achieved by nanowires. Random laser based on nanowire arrays has been achieved at a wavelength of 239 nm9 and 262.1 nm10. However, the optical power is still low. What’s more, the emitting wavelength is largely unstable and unpredictable because the cavity is defined by random multiple scattering.

Capture.PNG
Fig.1 Schematic for e-beam pumped light emitting device12

These drawbacks render both optically driven DUV laser and electrically driven random DUV laser impractical in outer space application. Another strategy is to drive the active material by the electron beam. In such lasers, the electron hole pair is generated by the energy transfer of high energy electron beam emitted from the e-gun. A direct benefit of this approach is that both p doping and n doping are unnecessary, alleviating absorption of p- and n- doped layer. High power green and blue electron-beam pumped laser have already been demonstrated with a maximum optical power of 5.9W (λ =530 nm) and 3.3W (λ =462 nm) at a moderate electron energy of 42 keV and 37keV11. DUV source emitting at 240 nm with a maximum power of 100 mW and a pumping power of 10 kV, a pumping current of 45 uA was also demonstrated12. The success of these devices demonstrates the great potential of e-beam pumped laser to achieve high power short wavelength DUV laser. 

Reference

1.           Li, X.-H., et al., Low-thresh old stimulated emission at 249 nm and 256 nm from AlGaN-based multiple-quantum-well lasers grown on sapphire substrates. Applied Physics Letters, 2014. 105(14): p. 141106.

2.           Li, X.-H., et al., Demonstration of transverse-magnetic deep-ultraviolet stimulated emission from AlGaN multiple-quantum-well lasers grown on a sapphire substrate. Applied Physics Letters, 2015. 106(4): p. 041115.

3.           Maxim, S., et al., Room-Temperature Stimulated Emission from AlN at 214 nm. Japanese Journal of Applied Physics, 2006. 45(12L): p. L1286.

4.           Lochner, Z., et al., Deep-ultraviolet lasing at 243 nm from photo-pumped AlGaN/AlN heterostructure on AlN substrate. Applied Physics Letters, 2013. 102(10): p. 101110.

5.           Kao, T.-T., et al., Sub-250 nm low-threshold deep-ultraviolet AlGaN-based heterostructure laser employing HfO2/SiO2 dielectric mirrors. Applied Physics Letters, 2013. 103(21): p. 211103.

6.           Yoshida, H., et al., A 342-nm ultraviolet AlGaN multiple-quantum-well laser diode. Nat Photon, 2008. 2(9): p. 551-554.

7.           Selles, J., et al., Deep-UV nitride-on-silicon microdisk lasers. Scientific Reports, 2016. 6.

8.           Zhu, H., et al., Low-threshold electrically pumped ultraviolet laser diode. Journal of Materials Chemistry, 2011. 21(9): p. 2848-2851.

9.           Zhao, S., et al., An electrically pumped 239 nm AlGaN nanowire laser operating at room temperature. Applied Physics Letters, 2016. 109(19): p. 191106.

10.         Zhao, S., et al., An electrically injected AlGaN nanowire laser operating in the ultraviolet-C band. Applied Physics Letters, 2015. 107(4): p. 043101.

11.         Klein, T., et al., High-power green and blue electron-beam pumped surface-emitting lasers using dielectric and epitaxial distributed Bragg reflectors. Journal of Applied Physics, 2015. 117(11).

12.         Oto, T., et al., 100 mW deep-ultraviolet emission from aluminium-nitride-based quantum wells pumped by an electron beam. Nature Photonics, 2010. 4(11): p. 767-771.


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