Study on (110)-QW Lasers with Low Threshold Current Density

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Threshold current densities of (110)-QW lasers were investigated for wide stripes aligned in the [001] and [110] directions from the same wafer. As there is no cleaved facets for lasers along [001] direction, the mirror facets were formed parallel to the (001) face by reactive-ion-etching (RIE) using BBr_3gas. The threshold current densities of the lasers aligned in the [001] direction are found to be much smaller than those aligned in the [110] direction. This strong anisotropy in J_<th> is believed to come from the stronger oscillator strength in the [001] direction cavity and will be very useful to control polrization of laser output from surface emitting lasers (SELs) if the (110) QW structure is used for the SELs. Fairly low threshold current densities of less than 0.6 KA/cm2 were obtained for the lasers with cavities along [001] direction in spite of the lower reflectivity of the RIE-etched mirror surface. With improved mirror reflectivity of the dry-etched (001) face, lower threshold current density will be obtained for the (110)-oriented GaInAs (P) QW lasers.The results in this research show the expected advantage of the (110) lasers along [001] cavity direction and suggests an advantage of the (110) QW structure in the application for long wavelength surface emitting lasers. This research might be very useful for the development of long wavelength vertical cavity surface emitting lasers, as the lasers need more optical gain to compensate their low reflectance of the cavity mirrors and polarization control of the emitting light.