Effects of intentionally introduced mismatch strain on the operating characteristics and temperature performance of indium gallium arsenic phosphide/indium phosphide long wavelength semiconductor lasers

Abstract

<p>An investigation into the effects of material strain on the temperature sensitivity and operating characteristics of InGaAsP/InP strained-layer multiple-quantum-well (MQW) ridge-waveguide lasers is reported. This thesis contains the first comparison between the performance of strained and unstrained all quaternary MQW lasers having, not only similar emission wavelength, but also identical quantum well thicknesses. Results show that significant improvements in device performance can be obtained through the application of strain. These improvements include: a substantial reduction in the temperature sensitivity of laser threshold current, Ith; a reduction in Ith; an increase in maximum output power; an increase in the maximum operating temperature; and, an increase in the internal device efficiency, η. From investigations into the effects of strain, and QW width on the temperature performance of InGaAsP/InP lasers, the root of the temperature sensitivity of Ith is found to be much more complicated than can be explained by a single dominant physical process, as proposed by other authors. In addition the exponential relationship proposed by Pankove in 1968, which is commonly used to describe the Ith-T sensitivity in terms of the parameter, To, is found to be inappropriate. A new, relationship to describe the variation of Ith with temperature for InGaAsP/InP based lasers is proposed, and the parameter To is replaced by the parameter Tmax which represents the lasers' maximum operating temperature. In addition an expression relating Tmax to adjustable device parameters, such as: cavity length; facet reflectivity; optical confinement factor; internal efficiency; and transparency current density, is derived mathematically from an empirically determined relationship between the temperature rate of change of the threshold current density, ∇TJth, and the threshold current density, Jth. Achieved are the highest reported maximum operating temperature (140℃) and largest characteristic temperature (To = 88 K) for InGaAsP based lasers.</p>