Low threshold current densities in red VCSELs

Abstract

In this work, we have investigated the design and metalorganic vapor-phase epitaxial growth of red vertical cavity surface-emitting lasers (VCSEL, emission wavelength around 650–680 nm) with respect to low threshold current densities and a reduced temperature dependence. A VCSEL in the red regime implies a combination of AlGaInP (cavity) and AlGaAs/AlAs (distributed Bragg reflectors). In order to check the influence of the epitaxially critical P/As-interface on the laser performance, we have grown edge-emitting lasers where we varied the distance between this interface and the active quantum wells. We observed no increase of the threshold currents even for small distances as necessary in VCSEL structures when applying an optimized switching sequence at these interfaces. Consequently, red VCSELs could be grown which showed continuous wave operation at room temperature (670 nm, 0.15 mW at 20°C). In order to improve the temperature sensitivity of these VCSELs, we have studied a large number of devices with well-defined misalignment between gain and Bragg mirror reflectivity. For lasers where this misalignment resulted in somewhat worse room temperature properties (e.g. threshold current densities around 800 A/cm 2), we found a clearly enhanced temperature stability.