SEMINÁRIO DO DEPARTAMENTO DE FÍSICA DOS MATERIAIS E MECÂNICA
“Semiconductor nanostructures by molecular beam epitaxy – from nanomembranes as virtual substrates and strain free, mesoscopic GaAs structures”
Dr. Christoph Deneke, Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais (LNNano/ CNPEM)
Dia: 27 de abril, quarta-feira, Sala de Seminários José Roberto Leite - Ed. Alessandro Volta (bloco C) - sala 110, às 14h
Abstract:
Semiconductor nanostructures grown by molecular beam epitaxy (BEM) build one of the backbones of nanotechnology in the last decades [1]. The Brazilian National Laboratory for Nanotechnology in Campinas (LNNano/CNPEM) established recently a new III-V MBE facility associated with the laboratory for surface science (LCS). In this seminar, I will give an overview of the LCS instrumentation and research activities. After shortly outlining our activities in scanning probe microscopy – these microscopes are open for external users, I will focus on our research lines involving MBE grown semiconductor nanostructures. In the first part, the latest results using these nanomembranes as virtual substrates for the growth of III-V semiconductors will be discussed [2–4]. Therefore, we investigate the growth of InAs on top of partly released, wrinkled InGaAs membranes. We find that the wrinkled membranes modulate the chemical surface potential resulting in InAs accumulation on top of the wrinkles. This modulation of the chemical surface potential not only allows a detailed examination of the diffusion behavior of the deposited InAs, but also provides means for predetermining the position of the InAs nanostructure formation. In the second part, I will present our latest results for fabricating strain free, mesoscopic GaAs structures by a combination of Ga assisted deoxidation, local droplet etching and overgrowth. We create an initial template by depositing Ga on top of an oxidized GaAs (001) substrate without As counter pressure. After our deposition and annealing process, hole structures are obtained. The holes are 20 nm deep and surrounded by an elongated GaAs mount of ca. 200x500 nm. In a systematic study, we overgrow the holes BIFUSP 3. with Al0.33Ga0.67As of different thicknesses. We observe a preservation of the mount shape and then with larger Al0.33Ga0.67As thicknesses an asymmetric closing of the holes. Finally, these holes are filled with different amounts of GaAs and a second barrier of Al0.33Ga0.67As is deposited. Carrying out photoluminescence (PL) measurements, we find good optical activity at room temperature and single quantum dot features at low temperature. The results demonstrate that this process allows fabricating a new class strain free of GaAs emitters. [1] W. P. McCray, Nature Nanotechnology 2, 259 (2007). [2] C. Deneke, A. Malachias, A. Rastelli, L. Merces, M. Huang, F. Cavallo, O. G. Schmidt, and M. G. Lagally, ACS Nano 6, 10287 (2012). [3] S. Filipe Covre da Silva, E. M. Lanzoni, V. de Araujo Barboza, A. Malachias, S. Kiravittaya, and C. Deneke, Nanotechnology 25, 455603 (2014). [4] S. F. C. da Silva, E. M. Lanzoni, A. Malachias, and C. Deneke, Journal of Crystal Growth 425, 39 (2015).
