NONLINEAR TRANSMISSION DYNAMICS OF ZNSXSE1-X/ZNSE AND ZNSXSE1-X/ZNSYSE1-Y (X-GREATER-THAN-Y) WAVE-GUIDE STRUCTURES

We investigate the nonlinear transmission properties of ZnSxSe1-x/ZnSe and ZnSxSe1-x/ZnSySe1-y (x > y) waveguides grown by MOVPE. All waveguides were designed as three-layer waveguides with either a ZnSxSe1-x or a ZnSe layer as guiding layer. The light-guiding structures are examined using a time-resolved ns-pulse pump-and-probe technique, with the probe beam propagating through the waveguide and the pump laser being focused onto the cap layer of the waveguide. We observe induced absorption and transmission of the sample close to the absorption edge under pump light irradiation. This can be understood in terms of free carrier absorption, many-body effects and heating of the sample. The waveguides with ZnSe as guiding layer show interference patterns in the transmission spectra with unusually large spacing between the maxima for energies 30 meV below the absorption edge. This feature is understood as beating between two guided modes of the waveguide and can be observed at room temperature. The creation of free carriers in the waveguide can suppress these patterns. For lower carrier densities a blue shift of the interference fringes is observed.