Manufacturing-tolerant compact red-emitting laser diode designs for next generation applications

Quantum well laser diodes with low far-field divergence remain a requirement for many applications such as optical interconnects and data networks, pump sources and next generation holographic red–green–blue displays requiring compact, high power, visible light sources with high spatial and spectral coherence. Many designs exist, but the structure must be easy to grow reproducibly, which has commercial advantages. The authors' low far-field divergence design widens the vertical mode in such a way as to decrease the far-field divergence without significantly reducing the confinement factor, thus keeping threshold current lower. In this study, the authors calculate the sensitivity of their design, which has high refractive index mode expansion layers inserted in the cladding, to unintentional variations in layer thickness and composition during growth. They obtain consistency in measured far-fields for three wafers grown over an interval of a year, with a full-width-half-maximum vertical far-field divergence of 17° for a narrow design (Design A) and just under 13° for a very narrow design (Design B). They have demonstrated a useful, reproducible design, adding to the range of versatile semiconductor lasers available for every application

Comparison of experimental and theoretical gain-current relations in GaInP quantum well lasers

The authors compare the results of a microscopic laser theory with gain and recombination currents obtained from experimental spontaneous emission spectra. The calculated absorption spectrum is first matched to that measured on a laser, ensuring that the quasi-Fermi levels for the calculation and the experiment (spontaneous emission and gain) are directly related. This allows one to determine the inhomogeneous broadening in their experimental samples. The only other inputs to the theory are literature values of the bulk material parameter. The authors then estimate the non-radiative recombination current associated with the well and wave-guide core from a comparison of measured and calculated recombination currents

Many-body effects in InAs/GaAs quantum dot laser structures

We have measured the gain peak energy of GaInAs quantum dot laser structures, relative to the absorption peak, as a function of injection. We have used a calculation to remove the effects of state filling in the inhomogeneous distribution and to estimate the carrier density in the dots. We have identified shifts, which we associate with many body effects, of up to 8 meV at room temperature at injection levels typical for laser operation of about 2.2 electrons per dot, producing a peak modal gain of 10 cm-1

InP quantum dot lasers with temperature insensitive operating wavelength

We quantify the mechanisms that govern the lasing wavelength in edge-emitting InP/AlGaInP quantum dot (QD) lasers, by characterising the constituent factors controlling the temperature dependence of the gain peak wavelength. We show that a regime exists where the temperature coefficient of the bandgap can be compensated by the increasing wavelength-shift associated with state-filling in the QD ensemble, necessary to recover the gain peak magnitude. We demonstrate cleaved-facet edge-emitting lasers with a wavelength temperature dependence of 0.03 nm/K, similar to the temperature dependence of a Bragg stack fabricated in this material and approximately a sixth of the dependence of the bandgap