Reliable InGaAsP/GaAs 40W lasers grown in solid source MBE with phosphorus-cracker
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Reliable InGaAsP/GaAs 40W lasers grown in solid source MBE with phosphorus-cracker G. K. Kuang, I. Hernandez, M. McElhinney, L. Zeng, B. Caliva, and R. Walker, Lasertel Inc., 7775 N. Casa Grande Hwy, Tucson, AZ-85743 ABSTRACT Laser structures with InGaAsP quantum well were grown on GaAs substrates in a solid source MBE system. Threshold current density Jth as low as 290A/cm2 and slope efficiency as high as 0.68W/A per facet were obtained for uncoated laser chips at 25oC. After 857 hours burn-in at 47A (corresponding to around 47W) at room temperature, power degradation rate was measured to be less than 3x10-6/h. INTRODUCTION 0.8µm lasers have become more and more attractive [1-3] as they have found great application in pumping solid-state lasers and in material processing. Lasers with InGaAsP Al-free active region have shown strong advantages over conventional AlGaAs lasers due to their resistance to dark-line defects [4], and high threshold of catastrophic optical damage (COD) [5]. For 0.8µm high power lasers, reliability is a common concern. In order to improve the laser reliability, a lot of research work has been reported. M. Razeghi et al have reported degradation rate of less than 2x10-5/h for uncoated InGaAsP lasers at facet load of 2 mW/µm in quasi-continuous wave regime [1]. J. Sebastian et al have studied large-optical-cavity (LOC) lasers with tensile strained GaAsP quantum well (QW), and reported degradation rate of less than 1x10-5/h for laser chips at facet load of 30 mW/µm at 25oC. For laser bars with the same epitaxial structure tested at facet load of around 16 mW/µm at 25oC, they obtained an extrapolated lifetime of over 5000 hours [3]. P. Bournes et al from Coherent Inc reported less than 1% degradation for 40W laser bars during 1300 hours operation at facet load of around 14 mW/µm at 25oC, which corresponded to a degradation rate of less than around 8x10-6/h [6]. In this paper we report on degradation rate less than 3x10-6/h obtained from 0.8µm lasers with LOC structure and Al-free active region grown in solid-source MBE with phosphorus-cracker. EXPERIMENT AND DISCUSSION The laser structure was grown on n-GaAs substrate at around 500oC. The growth sequence is as follows. At first a GaAs:Si buffer layer was grown mainly with As2 by using an As cracker cell. Then an AlGaInP:Si cladding layer and a GaInP waveguide layer were deposited, followed by an InGaAsP quantum well (QW). After the QW, similar waveguide layer GaInP and AlGaInP:Be cladding layer were deposited. In the end a GaAs contact layer heavily doped with Be was grown. All the phosphorus-containing layers were grown mainly with P2 by using a P cracker cell with cracker temperature of 850oC. During the growth, the V/III flux ratio was kept around 15. After growth, the wafer was characterized with photoluminescence (PL), X-ray diffraction and CV-profiler. XRD measurement shows that the lattice-mismatch of the epi-layers is less than 0.04%. Fig.1 shows the PL spectrum of the wafer at room temperature. It can be seen that the intensity
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