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Fabrication and characterization of strain balanced InAs quantum posts

AuthorsAlonso-Álvarez, Diego ; Alén, Benito ; Ripalda, José María ; Llorens Montolio, José Manuel ; Rivera de Mena, Antonio ; Taboada, Alfonso G.; González Díez, Yolanda ; González Sotos, Luisa ; Briones Fernández-Pola, Fernando
Issue Date2012
CitationICPS 2012
AbstractEpitaxial quantum dot (QD) solar cells need tens if not hundreds of QD layers in order to have an appreciable absorption at long wavelengths. In the InAs/GaAs system, due to the larger covalent radius of InAs, increasing the number and stack density of QDs layers inevitably leads to an increase of the strain fields and eventually to the formation of dislocations. The strain balanced (SB) technique consists of compensating the compressive stress introduced by the QDs by a tensile stress in the spacer between layers. In this way, by alternating tensile-compressive regions, the strain in the material is minimized and the formation of dislocations is retarded. Several groups have implemented their own combinations of materials in an attempt to stack many layers of QDs, either using P or N compounds. We have used this technique before to stack 50 InAs quantum dot layers in a solar cell structure with improved crystal quality and optical properties. In this work, we report on the fabrication and optical characterization of InAs quantum posts (QPs) grown using the above approximation in the limit of negligible spacer layer thickness. In order to achieve proper balancing of the accumulated stress, the growth of the samples was characterized by in situ real-time measurements of the total accumulated stress during growth. This technique allows us to monitor the accumulated compressive stress arising from the InAs layer and the tensile stress introduced by the compensating layer (GaAsP of different compositions). The resulting InAs/GaAsP quantum posts (QPs) are 120-nm-long vertical nanostructures which show a record height/diameter aspect ratio >7.4 We have embedded these nanostructures in a p-i-n diode structure to investigate their electro-optical properties as a function of temperature and applied bias. Our study reveals weak localization of carriers along the QP vertical axis at low excitation power and a one-dimensional-like density of states at high excitation.
DescriptionTrabajo presentado a la "31st International Conference on the Physics of Semiconductors" celebrada en Zurich (Suiza) del 29 de julio al 3 de Agosto de 2012.
Publisher version (URL)http://www.icps2012.ethz.ch/
Appears in Collections:(IMN-CNM) Comunicaciones congresos
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