Thermal analysis of InP lasers transfer printed to silicon photonics substrates

The thermal performance of Fabry-Perot InP lasers integrated onto different silicon photonics substrates by microtransfer printing is assessed. 500-μm-long ridge waveguide lasers on the original 350-μm-thick InP have an experimental thermal impedance, Z_EXP, of 57 K/W that is reduced to 38 K/W after printing to a 500-μm-thick Si substrate. Z_EXP for lasers printed on silicon-on-insulator wafers is ∼94 K/W, which is more than two times higher than that of the laser printed on the Si substrate. Z_EXP of lasers printed on thermally insulating layers like benzocyclobutene (BCB) or SiO₂ increases with the thickness of the layer. BCB adhesive layers as thin as 50 nm limit Z_EXP to be greater than 55 K/W. The thermal properties for the different situations were modeled using finite-element simulations which confirmed the experimental results within 10% accuracy. The simulations show how changes in the geometry and the materials of the integration platform can influence the resulting thermal impedance.