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

在近红外和中红外波长范围内发射的紧凑型光源在医学成像和诊断、远程示踪气体和空气污染监测以及电信中具有潜在的应用。根据应用，这些设备可能需要在非常窄的波长范围内发射，或者需要宽光谱输出，例如用于光学相干断层扫描。还可能需要调谐输出波长。基于III-V族化合物半导体的器件可以满足许多这样的应用。器件通常使用沉积在标准III-V二元衬底上的外延层结构制造;通常为GaAs、InP或GaSb。基于目标波长选择衬底，并且使用III族和V族元素的组成上更复杂的层的多个晶格匹配和/或薄应变层来生长器件结构。这些二元衬底的使用限制了晶格匹配组合物的范围，因此限制了可获得的波长范围。克服这种限制的方法是使用变质衬底层（MSL），其涉及以松弛应变的方式生长三元或四元III-V层的厚应变层，而不引起穿透位错，并且产生无缺陷的表面层，由于其不同的晶格常数，该表面层可以允许生长用于在先前不可接近的波长下产生器件的层。这可以应用于基于量子阱、量子线（QWR）和量子点（QD）的器件。这项研究提出了使用MSL方法可以发射高达3µm的光源的设计，制造和表征，其具体目标是利用为器件制造而开发的成熟InGaAsP四元化合物。还将制造基于QWR和QD的器件，以利用与这种器件的减小的维度相关联的固有优点。

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.