No abstract

In this work, we demonstrate theoretically that the piezoelectric effect can be used to achieve confinement over quantum distances in systems grown on [001] GaAs substrates. Such an effect can be achieved by making use of elastic relaxation of micromachined strained structures. At the free corners of the overhanging beams, shear deformations appear which induce a three-dimensional V-shape potential. Calculations show the creation of quantum dots near the corners of the overhanging beams.

We describe a method of lateral band gap modulation by creating steep lateral strain gradients in multiquantum (MQW) structures on InP. The strain modulation is obtained by controlled elastic relaxation of micromachined free-standing strained MQW stacks. Large lateral energy modulation is achieved, suitable for lateral optical mode confinement and lateral quantum confinement of excitons. It is pointed out that this technology can be applied in monolithic integration of semiconductor optical devices.

The mechanical relaxation of strained semiconducting stripes is studied. The deformation tensor is calculated using a classical approach of elasticity problem with predeformations; the electronic band structure is then simulated using an 8 band kp model including strain. To confirm the models developed, compressively and tensely strained stripes were fabricated and characterized by photoluminescence measurements. Theoretical and experimental results are in very good agreement and show the importance of mechanical anisotropic relaxation phenomena in optoelectronic devices like waveguide structures, modulators, or lasers.

In the field of III-V-based compounds, new functionalities can be reached by integrating micromechanical structures with electro-optical functions, in order to fabricate Micro Opto Electro Mechanical Systems (MOEMS). A possible application is an InP-based integrated optical stress sensor. Such a system is based on a partly suspended waveguide that can be strained under the effect of an external stress. The photoelastic effect induces a phase shift that can be converted into an intensity shift of the signal if the device is configurated as a Mach-Zehnder interferometer. This system can be integrated monolithically with the optical source and the photodetector. The mechanical, photoelastic and optical properties of this structure has been simulated in order to configurate the alloy composition of the epitaxial layers and the geometry of the device. Micromachining processes have been developed in order to realize InP-based suspended microstructures by sacrificial layer etching and bulk micromachining. Preliminary results showed that the optical behaviour of the waveguides is close to the theoretical analysis. Characterisation of the complete interferometer is underway in our group.