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Characteristics of Polyimide-planarized Oxide-confined Vertical-cavity Surface-emitting Laser (VCSEL) Diodes with Passive Heat Sinking
A.N. AL-Omari, A.M.K. Dagamseh, O.M. Khreis, A. Ababneh and K.L. Lear

An oxide-confined, dielectric-planarized, metal-plated, n-side up vertical-cavity surface-emitting laser (VCSEL) with 850 nm emitting wavelength was fabricated and characterized. 30 μm mesa diameter VCSELs with 10 μm active area diameter and 4 μm thick Cu plated heat sink displayed a maximum frequency modulation bandwidth, ƒ-3dB, of 16.4 GHz and a resonance frequency,ƒR, of 11.7 GHz at a low bias current density, Jb, of only 7.5 kA/cm2, which corresponds to a high ƒ-3dB 2/Jb ratio of 35.6 GHz2/kA/cm2. The achieved 7.5 kA/cm2 current density is less than the industrial benchmark current density for reliability, which is 10.0 kA/ cm2, by 25%. The reported devices demonstrated a modulation current efficiency factor of 9.7 GHz/mA1/2 and a D-factor of 6.5 GHz/mA1/2. Examination of the analogue modulation response (ƒ-3dBR ~1.41) demonstrated that the presented VCSELs did not suffer from high damping typically produced by self-heating and gain suppression. The measured thermal resistance was 1.01 ºC/mW, which corresponds to an improved distributed Bragg reflectors thermal conductivity of 0.50 W/cmK and a reduced VCSEL thermal resistance by approximately 62% compared to previously reported oxide-confined polyimide-wrapped VCSELs with similar epitaxial structure and dimensions. Threshold current density and series resistance were as low as 1.4 kA/cm2 and 60 Ω, respectively, with a maximum optical output power of 0.9 mW.

Keywords: Diode laser, semiconductor laser, vertical-cavity surface-emitting laser (VCSEL), polymide-planarized, oxide-confined, dielectric-planarized, high-speed modulation, thermal resistance

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