Tuning indium arsenide quantum dot electronic structure using (indium aluminum gallium)arsenide capping layers and application to infrared photodetectors.

摘要

This dissertation contributes to the subjects of (i) molecular beam epitaxical growth and characterization of strain-driven self-assembled InAs/GaAs coherent island based quantum dots (QDs), (ii) manipulation of such InAs QD electronic states and associated transitions utilizing Al_xGa _1−xAs, In_xGa_1−xAs, or In_xAl _yGa_1−x−yAs capping layers, and (iii) application of such InAs/(InAlGa)As QDs to infrared photodetectors (QDIPs).; A slow-growth-rate (at 0.054 ML/sec) QD formation is introduced to realize high-quality uniform InAs/(InAlGa)As QDs. Such QDs are characterized utilizing photoluminescence (PL), PL excitation spectroscopy, atomic force microscopy, and transmission electron microscopy. The QD growth kinetics is discussed by comparing with commonly employed relatively fast-growth-rate (at 0.22 ML/sec) QD formation.; To manipulate electronic states and associated transitions of such InAs/GaAs QDs, part of the GaAs capping layer is replaced with Al_xGa _1−xAs, In_xGa_1−xAs, or In_xAl_yGa_1−x−yAs layers. Al _xGa_1−xAs insertions result in blueshifted inter- and intraband transition wavelengths (with respect to those of InAs/GaAs QDs) because of the enhanced confinement potential. By contrast, In_xGa _1−xAs insertions allow redshifted inter- and intraband transition wavelengths because of overall lowering of the confinement potential via strain relief and chemical difference effects. Moreover, the In_xGa _1−xAs layer regions between the InAs QDs act as a quantum well (QW) having its own energy states. Indeed, we find that the long-wavelength IR (LWIR) photoresponse involves QD intraband transitions to final states that are likely coupled to the QW electron energy states. To further the objective of controlled manipulation of the electronic states in InAs QDs, we introduce the notion of a lateral potential confinement layer (LPCL) whose judicious placement during island capping allows selective impact on ground and excited electron and hole states.; Finally, as an application of self-assembled epitaxical island QDs, we have performed a comprehensive study on n-i(5 QD layers)-n QDIPs. The QDIP performance is significantly enhanced by introducing Al_xGa _1−xAs dark current blocking layers into the QDIP active regions. The Al_0.2Ga_0.8As-QDIP shows the highest 77 K detectivity for a QDIP to-date: 9.6 × 109 cmHz1/2/W at 6.2 μm. We also tailor detection bands of QDIPs to the LWIR (8–14 μm) regime using In_xGa_1−xAs strain-relieving capping layers that also act as QWs. (Abstract shortened by UMI.)