Abstract
Thin-film vertical cavity surface emitting lasers (VCSELs) mounted onto heatsinks open up the way toward low-power consumption and high-power operation, enabling them to be widely used for energy saving high-speed optical data communication and three-dimensional sensor applications. There are two conventional VCSEL polarity structures: p-on-n and n-on-p polarity. The former is more preferably used owing to the reduced series resistance of n-type bottom distributed Bragg reflection (DBR) as well as the lower defect densities of n-type GaAs substrates. In this study, the p-on-n structures of thin-film VCSELs, including an etch stop layer and a highly n-doped GaAs ohmic layer, were epitaxially grown in upright order by using low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The p-on-n structures of thin-film VCSELs were transferred onto an aluminum heatsink via a double-transfer technique, allowing the top-emitting thin-film VCSELs to keep the p-on-n polarity with the removal of the GaAs substrate. The threshold current (Ith) and voltage (Vth) of the fabricated top-emitting thin-film VCSELs were 1 mA and 2.8 V, respectively. The optical power was 7.7 mW at a rollover point of 16.1 mA.
Highlights
With the demand on high-speed data communication networks, vertical-cavity surface-emitting lasers (VCSELs) are considered as a prominent light source that is strongly favored for use in optical data links due to their low-power consumption and high-modulation speed at low threshold current, along with a low circular beam divergence that enables efficient optical coupling with other systems[1,2,3,4]
The adhesive wax was uniformly applied on the polyimide carrier at low temperature, which was bonded to the thin-film vertical cavity surface emitting lasers (VCSELs) with controlled pressure
The polyimide carrier was separated by selectively removing the wax, thereby the top-emitting 940-nm thin-film VCSELs mounted onto the aluminum substrate were successfully fabricated
Summary
With the demand on high-speed data communication networks, vertical-cavity surface-emitting lasers (VCSELs) are considered as a prominent light source that is strongly favored for use in optical data links due to their low-power consumption and high-modulation speed at low threshold current, along with a low circular beam divergence that enables efficient optical coupling with other systems[1,2,3,4]. The driving voltage of the substrate-removed thin-film VCSELs can be lowered due to the reduction of series resistance at the expense of considerably thick and moderately doped GaAs s ubstrates[17]. The thermal conductivity of Aluminum (2.47 W/ cm K), 4.57 times higher compared to that of a GaAs substrate (0.54 W/cm K), enables the high-power VCSELs operation due to the higher rollover current with the lowered thermal resistance. The top-emitting 940-nm thin-film VCSELs are successfully fabricated onto aluminum heatsinks via a transfer approach that utilizes a double-transfer process with a polyimide carrier, an aluminum heatsink, and adhesive materials such as wax, silver-filled epoxy. The fabricated thin-film VCSELs are investigated using optical spectrum and light–current–voltage (L–I–V) curves
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