GaAs / Alx Ga1-x As Quantentöpfe: MBE-Wachstum, Charakterisierung und laterale Modulation mittels fokussierter Ionenstrahlen

Product Description

The properties of low-dimensional systems are of particular interest both for fundamental physical research and for technological applications. The systems enable the investigation of physics in small dimensions, show surprising novel physical properties and at the same time offer a broad spectrum of possible application areas. This work deals with the MBE growth of GaAs/AlAs quantum wells and the lateral modulation of their optical and electronic properties by focused ion beams. The characterization of the produced samples was carried out by means of photoluminescence measurements. In the first part of the work, quantum wells were produced with molecular beam epitaxy, which served as starting material for the lateral modulation. The growth parameters and layer structures were optimized with regard to the luminescence properties. The achieved linewidths for quantum wells with widths of 19.8, 15.2, 12.2, 9.9, and 5.6 nm amount to 0.18, 0.37, 0.46, 0.81 and 1.24 meV and were achieved in samples with short-period GaAs/AlAs superlattices as barriers. Additionally, the temperature dependence of the band gap and the linewidth as a function of the quantum well width investigated. The second part of the work deals with the lateral modulation of the band gap and the refractive index of quantum wells by means of focused ion beams, whereby the influence of the barrier type, as well as the depth distribution of the implantation-induced intermixing were investigated. The results of the investigation show that the interdiffusion depends strongly on the barrier type. The strongest interdiffusion is achieved with short-period superlattice barriers. To achieve maximum intermixing and thus efficient modulation with the lowest possible implantation damage, knowledge of the depth distribution of the ions or vacancies in the crystal is necessary. The maximum of this distribution determines the depth of the quantum well at which maximum intermixing occurs for a given implantation dose. The depth distribution of the 100 keV Ga+ ions was determined experimentally for implantation directions both perpendicular and 7° tilted to the (001) GaAs surface. The maximum of this distribution lies at about 70 nm for the perpendicular or 60 nm for the tilted implantation direction and thus deviates 40 nm or 30 nm from the simulation results (SRIM 2000). The experimental results show that channeling causes a significant shift of the distribution maximum of about 10 nm, although the