Far field pattern of AlGaN cladding free blue laser diodes grown by PAMBE

Grzegorz Muziol 1Henryk Turski 1M. Siekacz 1,2Marta Sawicka 1,2Paweł Wolny 1Emilia Pruszyńska-Karbownik 3Kazimierz Regiński 3Bohdan Mroziewicz 3Piotr Perlin 1,2Czeslaw Skierbiszewski 1,2

1. Polish Academy of Sciences, Institute of High Pressure Physics (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
2. TopGaN LTd, Sokolowska 29/37, Warszawa 01-142, Poland
3. Institute of Electron Technology (ITE), al. Lotników 32/46, Warszawa 02-668, Poland


Electrically driven laser operation from InGaN based devices had been shown in wide optical range from UV to green. Applications of laser diodes (LDs) to data storage technology and laser projectors demand very high beam quality. Nitride based LDs suffer from leakage of optical modes to GaN substrate which is pronounced as ripples in the far field pattern [1] which significantly worsens the beam quality. The amount of light leaking to the substrate increases for LDs emitting at longer wavelengths.
Leakage of optical modes to GaN substrate is often reduced by increasing the n-type AlGaN cladding thickness. Strauss et al. had shown that for LDs emitting at λ=440 nm a cladding as thick as 3 µm is needed to fully suppress ripples in far field pattern and obtain a Gaussian shaped beam. Growth of such thick AlGaN claddings without cracks in the structure is demanding for epitaxy.
In this work we present another way to obtain Gaussian shaped far field pattern for blue LDs. We have grown AlGaN cladding free LDs by Plasma Assisted Molecular Beam Epitaxy (PAMBE) [3,4], where the optical mode is confined by thick, high In content InGaN waveguide. Growth of thick high quality InGaN layers needed for waveguides is crucial to obtain good LD characteristics. Recent advantages in understanding of growth mode of high In content InGaN layers by PAMBE [5] allowed us to obtain high quality InGaN waveguide.
Due to the fact that effective refractive index of the light propagating in InGaN waveguide is higher than refractive index of GaN there is no leakage of optical modes to the GaN substrate. We show Gaussian shaped far field patterns with no ripples. AlGaN cladding free blue and green LDs can prove to be the choice for new generation laser projectors.

[1] V. Laino et al., Substrate Modes of (Al,In)GaN Semiconductor Laser Diodes on SiC and GaN Substrates, IEEE Journal of Quantum Electronics, vol.43, no.1, pp.16,24, Jan. 2007 
[2] U. Strauss et al., Beam quality of blue InGaN laser for projection, Phys. Status Solidi C 5 (2008) 2077 
[3] C. Skierbiszewski et al., AlGaN-Free Laser Diodes by Plasma-Assisted Molecular Beam Epitaxy, Appl. Phys. Express 5 (2012) 022104
[4] C. Skierbiszewski et al., True-Blue Nitride Laser Diodes Grown by Plasma-Assisted Molecular Beam Epitaxy, Appl. Phys. Express 5 (2012) 112103
[5] H. Turski et al., Nonequivalent atomic step edges—Role of gallium and nitrogen atoms in the growth of InGaN layers, Journal of Crystal Growth, Volume 367, 15 March 2013, Pages 115-121

Acknowledgements: This work was supported partially by the Polish Ministry of Science and Higher Education Grants No IT 13426 and INNOTECH 157829.


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Presentation: Poster at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Topical Session 3, by Grzegorz Muziol
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-15 21:02
Revised:   2013-04-15 21:08