Design Considerations for Single-Mode Vertical-Cavity Surface-Emitting Lasers With Impurity-Induced Intermixing

We report on the modeling of 850-nm (Al,Ga) As/GaAs vertical cavity surface-emitting lasers (VCSELs), where the electrical and optical confinement is realized by impurity-induced intermixing. The 3-D simulations of electromagnetic fields are performed by the finite-element method using full vector Maxwell's equations. An example of a transverse junction VCSEL with Zn-induced intermixing of the areas surrounding the quantum well region is compared with the case of a VCSEL, where the optical modes are confined by selective oxidation of the Al-rich GaAlAs aperture layers. We show that Zn-induced intermixing results in a high efficiency of the leakage of the VCSEL aperture-confined modes into the surrounding intermixed area. Furthermore, there is a strong mode selectivity through the leakage loss between the fundamental and excited transverse modes of the optical cavity. This enables potential realization of a single transverse mode VCSEL at the aperture diameters of 10 mu m or above and consequently the realization of high-power single-mode VCSELs. Optimum mode selectivity is realized once the impurity intermixing profile proceeds down to the depth of about 2.6 mu m into the bottom distributed Bragg reflector below the quantum well region. Leakage of the optical modes into the intermixed area is accompanied by the evolution of narrow tilted lobes in the far-field emission spectra (at similar to 60 degrees tilt angles for the design considered). This effect is similar to the one previously observed in oxide-confined leaky VCSELs and originates from the laterally propagating optical modes outside the non-intermixed aperture region. Where necessary, by applying such phenomenon, a phase-coupled array can be configured. We believe that such single-mode VCSELs may become extremely important in 3-D sensing, printing, and laser illumination. Furthermore, LIDARs with an option of beam steering without moving parts can be realized in 2-D phase-coupled arrays.