Optimized design parameters of InGaAsInP quantum well lasers

Abstract

A complete theoretical analysis is carried out for the design of a lattice matched InGaAsInP quantum well (QW) laser taking into account carrier collection, intraband relaxation and emplying dipole moment matrix elements for gain calculations. The effects of temperature, carrier concentration, and well width on the linear gain are studied. The maximum gain vs. current density curves are obtained for multiple temperatures and well width conditions. It is seen that for operation with carrier concentration above 2 × 10 −18 cm −3, maximum gain decreases with increase in well width. A significant reduction in gain is observed as the temperature increases. The gain spectra for In 0.53Ga 0.47AsInP QW structure for TE modes, display a gradual increase at the transition energy when broadening due to intraband relaxation is taken into account. However, with broadening, gain peaks are not fixed at the wavelengths determined by transitions between the quantized levels but are seen to be shifted towards shorter wavelengths for finite values of intraband relaxation time. For a given facet reflectivity, well width laser losses and length of the laser, a single quantum well may not give the lowest current to achieve lasing. By increasing the number of wells, the threshold current can be decreased. The approach for optimising the QW to achieve the lowest threshold is presented. Similarly, for a given facet reflectivity, well width, laser losses and the number of quantum wells, the length of the cavity can also be optimized to reduce the threshold current.