Photonic Systems Brown Bag Seminar

Quantum Wells on Graded Buffers for Laser Diodes beyond 1.3 um on GaAs

Henry Choy

For a long time, there has been a desire to extend the emission wavelength of GaAs-based quantum well (QW) lasers, with the aim of eventually replacing InP with GaAs as the substrate of choice for communication applications.  Using dilute nitride GaInAsN QWs or InAs quantum dots, emission wavelengths have successfully been extended to 1.3 um, but significant difficulties have been met going beyond 1.3 um.  In this talk, we will discuss an alternative approach, namely, the MBE growth of QWs on top of compositionally InGaAs graded buffers, with the indium composition in the buffers linearly graded from 0% to 15% or 20%.  We have observed that one can obtain strong QW emission on top of such graded buffers only under a very restricted range of growth conditions, which are not compatible with the subsequent growth of the aluminum-containing barriers necessary for carrier confinement.  Furthermore, upon proper ex-situ annealing, we were then able to obtain QW emission as strong as, sometimes even stronger than from QWs pseudomorphically grown on GaAs.  However, when even slight tensile or compressive strain was added to the QWs, severe degradation occurred, which could be correlated with the amount of surface roughness.  This talk will both review this work, and provide a critical assessment of the prospects for achieving the goal of growing 1.55 um laser diodes on GaAs substrates.