Temperature dependence and material properties of InGaAsP/InP mirrors

The authors have measured and modeled the temperature characteristics and material properties of quarter wavelength mirrors made using InP and InGaAsP. The center wavelength of the mirror moves at 0.110 nm/ degrees C, in good agreement with the theory. This is an important result for the thermal design of such devices as VCSELs. This result can be used to find the shift in the resonant mode of the cavity or the change in penetration depth of the mirror with temperature. The authors have also characterized the reflectivity and bandwidth of this mirror as a function of the number of layers. Using selective wet chemical etchants, they removed one layer at a time and then measured the spectrum of the mirror. From this structural analysis, it was found that the center wavelength is much more sensitive than the bandwidth or peak reflectivity in detecting drift in layer thicknesses. This technique can be used to find the actual reflectivity for different numbers of layers without resorting to several expensive, time-consuming mirror growths. The measured reflectivity and bandwidth are in good agreement with theory.<>