Limits of electro-absorption in high purity GaAs, and the optimisation of waveguide devices

An alternative theoretical treatment for electro-absorption at the fundamental absorption edge of semiconductors is compared with experimental results in high purity MOCVD grown GaAs. For the first time, acceptable agreement between theory and experiment is demonstrated for wide ranges of wavelengths (0.85–1.0 μm), and applied fields (up to the breakdown field). It is shown that these results enable optimised electroabsorption modulators to be designed for low insertion loss, high extinction ratio, high cut off frequency, and wide optical bandwidth. The feasibility of waveguide device with performance parameters higher than any reported to date (with or without the use of quantum wells) is predicted, and experimental devices are reported which approach these predictions at low frequencies of operation.