This work focuses on how to achieve high power, low threshold, and high efficiency single mode VCSELs. Various mechanisms that affect the differential quantumefficiency and threshold current of the proton-implanted and oxide-confined photonic crystal vertical-cavity surface-emitting lasers (VCSELs) are studied. Three degrees of freedom in designing the photonic crystal VCSELs to maximize the laser performance interms of efficiency and threshold current are considered: the epitaxial structure, the relative size of the current aperture and the transverse optical mode, and the photonic crystal design. The theoretical background regarding the differential quantum efficiencyand threshold current of the photonic crystal VCSELs is presented. Proton-implanted 850 nm VCSELs intended for high efficiency single mode lasing are fabricated and characterized, and then the experimental results are compared with the theories. It isfound that spectral and spatial mode-gain overlap, optical loss, and thermal effects affect the laser efficiency and threshold current. The thermal effects also affect the dynamical change of differential quantum efficiency with the injected current. The epitaxial structure determines the spectral mode-gain overlap and the modal properties of the VCSELs, while the relative size of the current aperture and the optical mode sets the spatial mode-gain overlap factor. The photonic crystal air hole fill-factor has an impact on all the mechanisms mentioned above. By etching the photonic crystal into proton-implanted VCSELs, stronger index guiding is introduced and consequently the wide distribution of efficiency and threshold current between devices and the discontinuity in measured output power versus current are eliminated, and the threshold current is reduced. Single mode power of 2.5 mW is obtained from proton-implanted photonic crystal VCSELs.
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