Quaternary Indium Gallium Aluminum Arsenide/indium Aluminum Arsenide Quantum Wells for 1.3 Micron Electroabsorption Modulators.

Properties of quaternary InGaAlAs/InAlAs multiple quantum wells have been investigated for 1.3 mu m electroabsorption modulator applications. This work is motivated by the lack of easily assessable and reproducible MQW materials to provide electroabsorption modulation at the important optical wavelength of 1.3 mum. There has also been a need for guidelines to the optimization of MQWs for efficient modulators. Quaternary rm (In_{x }Ga_{1-x}As)_{1-z}(In _{y}Al_{1-y}As)_ {z}/In_ {y}Al_{1 -y}As multiple quantum wells were synthesized via the readily available solid-source molecular beam epitaxy. The compositions x ~ 0.53 and y ~ 0.52 were chosen to satisfy lattice-matching condition on InP substrates. The compositions z in the range of 0.25 ~ 0.35 have been chosen to obtain an absorption edge in the vicinity of 1.3 mum. Experimental investigations have been carried out to optimize the substrate surface preparation procedure, growth conditions, and composition controls. Studies on the absorption lineshape and linewidth parameters have been emphasized. An exponential absorption tail is necessary to fit the exciton absorption edge in addition to the absorption peak in Gaussian lineshape. Low -temperature luminescence and variable temperature absorption spectroscopy revealed that alloy related inhomogeneous broadening and LO-photon related homogeneous broadening both have significant contribution to the broader room -temperature absorption linewidth. Room-temperature electroabsorption due to the quantum confined Stark effects has been investigated extensively to confirm theoretical calculations and to established empirical lineshape and linewidth parameters. Based on these results, a semi-empirical model has been established and have successfully predicted electroabsorption spectra in agreement with experimental data. Analyses for digital and analog signal transmission yield specific figures of merit for electroabsorption characteristics. In terms of these parameters, the optimization of this quantum well materials have been discussed. Simulated and experimental data have been compared to verify theoretical predictions and to determine the practical limitations. The extended absorption tail has detrimental effects on digital modulation characteristics. The performance parameters of modulators for both digital and analog applications depend critically on the linewidths of the exciton absorption peak.