Quantum well intermixing in 1.55 um InGaAs/AlInGaAs and InGaAs/InGaAsP structures and applications
The work described in this thesis is aimed at the exploring the possibility of optically integrating multi-bandgap energy devices on appropriate semiconductor substrates, using the technology of quantum well intermixing. A novel quantum well intermixing technique, based on sputtering process induced disordering (SID), has been developed for the first time, addressing multi-bandgap active device integration. Using this technique, blue shifts have been precisely tuned from 0 nm to over 160 nm for the InGaAs/AlInGaAs and from 0 nm to 100 nm for the InGaAs/InGaAsP MQW systems. Assessment of post-process material characteristics has shown that good electrical and optical qualities were maintained in the bandgap widened regions of both the InGaAs/AlInGaAs and InGaAs/InGaAsP material systems. This novel technique has been used to create multi-wavelength light sources that are of potential application in WDM systems and 2x2 crosspoint optical integrated switches. The expected performance has been achieved. A reactive ion etching process, using CH4/H2 etching gas, has been investigated, particularly for effective etching in the InGaAs/AlInGaAs MQW system. A 'standard' process for the InGaAs/AlInGaAs material system has been developed, based on experimental research. Modelling and design of 3-dB MMI couplers have been carried out. An improved Ti/Si02 mask for reactive ion etching has been successfully employed to ensure the waveguide profiles of fabricated MMI couplers meet the design specification, especially regarding the lateral profiles of the MMI section. Characterisation has shown the waveguide profile is close to the design requirement (side wall angle is of 81±2°). The principle operation of the so-called terahertz optical asymmetric demultiplexer has been qualitatively described and the design of a Mach-Zehnder interferometer (MZI) type demultiplexer has been carried out. Three kinds of MZI demultiplexers with different geometric structures have been fabricated using SID technique. Assessment of the devices has been carried out, including the operation of semiconductor amplifier, propagation loss of the device, etc.