III-V-based semiconductor quantum structures for mid-infrared light emitting devices

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Compact light sources that emit in the near- and mid-infrared wavelength range have potential applications in medical imaging and diagnostics, remote trace gas and air pollution monitoring, and telecommunications. Depending on the application these devices may need to emit over a very narrow wavelength range or require a broad spectral output such as used for Optical Coherence Tomography. It may also be necessary to tune the output wavelength. III-V compound semiconductor-based devices can satisfy many such applications. Devices are usually fabricated using epitaxial layer structures deposited on standard III-V binary substrates; typically GaAs, InP or GaSb. The substrate is chosen based on the target wavelength and the device structure is grown using multiple lattice-matched and/or thin strained layers of compositionally more complex layers of the group III and group V elements. The use of these binary substrates limits the range of lattice-matched compositions and hence the range of wavelengths accessible. A way to overcome this limitation is to use metamorphic substrate layers (MSL) which involves growing thick strained layers of ternary or quaternary III-V layers in a way that relaxes the strain, without causing threading dislocations, and producing a defect-free surface layer that, because of its different lattice constant, can allow layers to be grown for producing devices at previously inaccessible wavelengths. This can be applied to quantum well, quantum wire (QWR) and quantum dot (QD) based devices. This research proposes the design, fabrication and characterization of light sources that can emit at up to 3µm using the MSL approach with the specific goal of utilizing the well established InGaAsP quaternary compounds which are well developed for device manufacturing. QWR and QD based devices will also be fabricated to exploit the inherent advantages associated with the reduced dimensionality of such devices.