Threshold Fluence Measurement for Laser Liftoff of InP Thin Films by Selective Absorption

摘要

abstract_textpWe explore conditions for achieving laser liftoff in epitaxially grown heterojunctions, in which single crystal thin films can be separated from their growth substrates using a selectively absorbing buried intermediate layer. Because this highly non-linear process is subject to a variety of process instabilities, it is essential to accurately characterize the parameters resulting in liftoff. Here, we present an InP/InGaAs/InP heterojunction as a model system for such characterization. We show separation of InP thin films from single crystal InP growth substrates, wherein a approximate to 10 ns, Nd: YAG laser pulse selectively heats a coherently strained, buried InGaAs layer. We develop a technique to measure liftoff threshold fluences within an inhomogeneous laser spatial profile, and apply this technique to determine threshold fluences of the order 0.5 J cm(-2) for our specimens. We find that the fluence at the InGaAs layer is limited by non-linear absorption and InP surface damage at high powers, and measure the energy transmission in an InP substrate from 0 to 8 J cm(-2). Characterization of the ejected thin films shows crack-free, single crystal InP. Finally, we present evidence that the hot InGaAs initiates a liquid phase front that travels into the InP substrate during liftoff./p/abstract_text