Comparison of 980 nm VCSELs with varying monolithic high contrast grating top coupling mirror designs

We design, fabricate, characterize, and compare 980 nm vertical cavity surface emitting lasers (VCSELs) with monolithic high contrast gratings (MHCGs) as top coupling mirrors. The MHCG is a series of parallel, rectangular stripes etched into a uniform GaAs epitaxial surface layer via electron-beam lithography and inductively coupled reactive ion etching, with specific grating period, height, and fill factor (defined as the grating bar width divided by the grating period). To boost the MHCG's optical power reflectance at 980 nm and the width of the optical stopband we add a 5.5-period p-doped distributed Bragg reflector (DBR) beneath the MHCG grating, thus forming a composite DBR plus MHCG top coupling mirror. The bottom n-doped DBR is a conventional all-semiconductor AlGaAs/GaAs DBR with 37-periods on a GaAs substrate. We fabricate single 980 nm DBR MHCG VCSELs with two oxide aperture diameters on quarter wafer pieces from starting 3- inch diameter VCSEL epitaxial wafers. Each quarter wafer contains six complete unit cells, and each unit cell is a twodimensional array of single VCSELs in 16 rows and 15 columns. We for example set a constant but different grating period in five of the unit cells and vary the grating fill factors from column to column and we vary the oxide aperture diameters from 1 to 9 Pm in the rows, thus yielding a large variety of VCSEL diodes with differing MHCG parameters for us to compare. We perform room temperature on-wafer probe testing of the static optical output power-current-voltage (LIV) characteristics and emission spectra and compare the impact of the grating designs on these test results. We report record static LIV performance for our DBR MHCG VCSELs with threshold current below 1 mA and optical output power exceeding 1.3 mW. We observe room temperature bias current dependent mode emission for example single mode wavelength tuning ranges up to 12 nm.