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Efficiency of InGaAs/GaAs Quantum Well Laser Stripes with 30 µm-Mesa
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Efficiency of InGaAs/GaAs Quantum Well Laser Stripes with 30 µm-Mesa

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I. R. Tagaca, J. Fernandez Jr., A. Somintac and A. Salvador , “Efficiency of InGaAs/GaAs quantum well laser stripes …

I. R. Tagaca, J. Fernandez Jr., A. Somintac and A. Salvador , “Efficiency of InGaAs/GaAs quantum well laser stripes
with 30 μm-mesa”, Proc. of 23rd Samahang Pisika ng Pilipinas Physics Congress, Iloilo City, October 2005.

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  • 1. Efficiency of InGaAs/GaAs Quantum Well Laser Stripes with 30 µm-Mesa I. R. Tagaca, J. Fernandez Jr., A. Somintac and A. Salvador Condensed Matter Physics Laboratory, National Institute of Physics University of the Philippines, Diliman, Quezon City 1101 Efficiency of MBE-grown InGaAs/GaAs quantum well (QW) laser stripes fabricated with 30 µm mesa (Figs. 1 to 3) is determined at its lasing wavelength ~ 0.98µm. The lowest threshold current density ( J th ) measured is ~ 600A/cm 2 (for cavity length l = 0.4 mm), much better than the last reported (2004) J th ~ 4400 A/cm 2 from a similar laser with 75µm mesa.[1] Room-temperature output power vs. injection current ( L-I ) curves at one laser facet estimate the internal quantum efficiency ( η i = fraction of injected carriers that stimulate emission of photons) and the internal absorption loss ( α i ) to be η i = 83 ± 23 % (with correction factor ( cf )) and α i = 75 ± 24 cm -1 (Fig. 4). The correction factor to the output power takes into account the undetected light due to elliptically diverging beam of the laser as verified by its far-field distributions. Acknowledgment We would like to thank the DOST-PCASTRD and UP-OVCRD for their continued support. Reference [1] G. Manasan, “Fabrication and Characterization of MBE-grown GaAs -based Lasers”, BS Thesis, University of the Philippines-Diliman, 2003. Figure 3 (a) Emission Spectra at LED ( λ = 0.98 µm, I < I th ) and laser ( λ = 0.96 µm) operation. LED intensity was magnified several times to emphasize linewidth collapse (from ~400 Å to ~4Å) when the device lases. Shift in λ is due to subsequent device heating. (b) Pulsed L-I curves (0.01% DC, 1kHz) from laser with l = 0.4 mm. Lasing occurs at the region where the L-I slope steeply rises. (a) (b) Figure 4 From η e -1 vs. l , home-grown lasers have α i = 75 ± 24 cm -1 , η i ~ 83 ± 23 % (no cf ) and η i ~ 25 ± 7 % (with cf ). η e is the fraction of carriers responsible for photons transmitted out of the laser Figure 2 Top view of an array of fabricated 1.5 mm-long lasers. Without polyimide, electrical access is by metal contacts about the width of white strip. (b) Figure 1 (a) SEM photograph and (b) schematic cross-section of the 30-  m mesa InGaAs laser stripe. The low quantum dot (QD) density (hence, few recombination sites) was inadequate to make the device lase at intended λ ~ 1.1 µm and even contributed to high α i (QDs absorb the higher energy emitted by the QW) . (a)

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