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978-3-8439-1676-9, Reihe Physik
Static and Transient Capacitance Investigations on GaAs and InAs Quantum Dots
119 Seiten, Dissertation Universität Hamburg (2014), Softcover, A5
In this thesis morphological as well as electronic and optical investigations on quantum structures grown by molecular beam epitaxy (MBE) are presented. Nanoholes fabricated by means of local droplet etching (LDE) are utilized for the fabrication of GaAs quantum dots (QDs) and air-gap heterostructures. The Stranski-Krastanov growth mode yields a different approach to the QD formation. The thus resulting InAs QDs are investigated by means of transient capacitance measurements within this work.
In the first part of this thesis MBE is introduced and the fabrication of QDs and air-gap heterostructures is described. In order to increase the nanohole density in LDE a multiple local droplet etching (MLDE) process is established. Etching with Aluminum droplets on AlAs is investigated and a high uniformity of the MLDE-nanoholes is obtained. In addition to this finding, at high etching temperatures the nanohole density becomes independent of the etching temperature, which is attributed to a change in the surface reconstruction.
The experimental methods used in this thesis are briefly described in the third part. CV profiling and magneto-transport yield information about the concentration of deep traps in Schottky-diodes. Admittance spectroscopy and static capacitance spectroscopy are employed for the investigation of GaAs QDs. InAs QDs are investigated by means of deep level transient spectroscopy (DLTS) and reverse biased DLTS (RDLTS). These methods are briefly introduced.
In the last part of the thesis the experimental results are presented. Optical reflection measurements on air-gap heterostructures are fitted with simulations performed by means of the transfer matrix method which reveals the air-gap structure. Possible matrix materials for GaAs QDs are investigated by CV profiling and magneto-transport. Following from these investigations, the GaAs QDs are embedded in AlAs and measured with admittance spectroscopy and capacitance spectroscopy. InAs QDs are examined with DLTS and RDLTS. The obtained results are successfully simulated utilizing a model considering PAT. The carrier dynamics in InAs QDs is addressed with charge selective DLTS. Activation energies and capture cross sections obtained from emission and capture are compared. The activation energies are almost equal, whereas the capture cross sections differ clearly.