Refine
Document Type
- Doctoral thesis (2)
Has Fulltext
- yes (2)
Is part of the Bibliography
- no (2)
Year of publication
- 2017 (2) (remove)
Language
- English (2)
Keywords
- BCM1F (1)
- Beam loss (1)
- CMS (1)
- CZTS (1)
- Diamant (1)
- Diamond (1)
- Dünnschichtsolarzelle (1)
- Grenzflächenphysik (1)
- Interface analysis (1)
- Kesterit (1)
Institute
The LHC is the largest particle accelerator and storage ring in the world, used to investigate fundamentals of particle physics and to develop at the same time the technology of accelerators and detectors. Four main experiments (ATLAS, ALICE, CMS and LHCb) , located around the LHC ring, provide insight into the nature of particles and search for answers to as yet unexplained phenomena in the universe. Two proton or heavy ion beams circulate in the LHC and are brought into collision in the four experiments.
The physics potential of each experiment is determined by the luminosity, which is a ratio of the number of the events during a certain time period to the cross section of a physics process. A measurement of the luminosity is therefore essential to determine the cross section of interesting physics processes.
In addition, safe and high-quality data-taking requires stable beam conditions with almost no beam losses. Each experiment has its own detectors to measure beam losses, hereafter called machine induced background. One such detector is installed in CMS, BCM1F. Based on diamond sensors it was designed and built to measure both, the luminosity and the machine induced background. BCM1F ran smoothly during the first LHC running period from 2009-2012 and delivered valuable beam loss and luminosity information to the control rooms of CMS and LHC. At the end of 2012 the LHC was shut down to improve the performance by increasing the proton energy to 7TeV and decreasing the proton bunch spacing to 25ns. Due to the success of BCM1F an upgrade of its sensors and readout components was planned in order to fulfil the new requirements.
The upgrade of the sensors comprises a two pad instead of one pad metallization. 24 instead of the previous 8 single crystal diamond sensors were foreseen for the new BCM1F to enhance the robustness and redundancy. To instrument BCM1F, 59 sensors were electrically characterized by measuring the leakage current, signal stability and charge collection efficiency. Quality criteria were defined to select sensors for the final installation. An overview of these measurements including a summary of the results is given in this thesis. In addition, an upgraded amplifier was developed within the collaboration in 130nm CMOS technology. It has a peaking time of 7ns instead of the 22ns of the one previously installed. A BCM1F prototype comprising a two pad sensor and the upgraded amplifier was tested at the DESY-II accelerator in a 5GeV electron beam. Results of these test-beam measurements are presented in this thesis as well as simulations to interpret the measurements.
The installation of the upgraded BCM1F was completed in 2014. In 2015 BCM1F was commissioned and started to measure luminosity and machine induced background. At the end, the thesis will describe both types of measurements with the focus on machine induced background demonstrating the functionality of BCM1F.
The chemical and electronic structure of the interfaces of kesterite-based and related absorber materials in thin-film solar cell device-relevant layer stacks have been investigated with x-ray based spectroscopic techniques (XPS, HAXPES, XAES, XES, and XAS). The analyzed materials are CZTS absorbers with their interfaces to the Mo back contact and to different Zn(O,S)-buffer layers, SnS absorbers with partly N-doped ZnO buffer layers, and 2 absorbers with (Cd,Zn)S buffer layers.
We find an unchanged CZTS surface in this series which has a profound effect on the ZnOS growth. Instead of a constant composition throughout the buffer thickness, we find S-rich material growing directly on the CZTS in the ALD process. The conduction band offset is found to be around -0.21(+-0.15) eV. The measured cliff is reduced by chemical interface modification towards a flat band alignment.
The interface effect during annealing at the CZTS back contact where MoS2 forms occurs even at low annealing temperatures below 500°C. Sn spectra of liftoff CZTS back sides, annealed on the Mo contact, resemble the precursor at all temperatures while Sn spectra of CZTS front sides are almost single phase after standard annealing. A TiN interlayer was effectively introduced to prevent reactions at the CZTS/Mo interface.
We find a strong impact of ALD deposited ZnO on oxidized SnS absorber surfaces, resulting in metallic Sn formation. In contrast, doped ZnO:N reduces the SnS much less agressively. The strong downwards bending for both ZnO and SnS at the ZnO/SnS junction that we find for undoped ZnO contact layers is drastically reduced if ZnO:N contact layers are used. The smaller cliff in the conduction band of 0.2 eV for ZnO:N/SnS makes this junction much more interesting for solar cell applications than the ZnO/SnS with a large cliff of 0.55 eV.
The chemical analysis of the (Cd,Zn)S:Ga/CuSbS2 reveals chemical interaction at the junction. We find an additional species on the high energy side of the Cu peak for all samples. The interface species can be explained with the changed buffer composition at the interface, particularly low S and Cd content and increased Ga concentration, and could also be affected by the presence of O and hydroxides. We find an upwards surface band bending of -0.15 eV for the bare absorber. At the junction, we see downwards band bending of up to 0.2(+-0.09) eV in the absorber and strong upwards band bending of -0.75(+-0.28) eV in the buffer. The junction is not an abrupt transition from one homogenious material to another. The buffer growth is strongly affected by the absorber. Also the electronic structure on both sides is significantly affected. We find a conduction band alignment with a large cliff of -1.3(+-0.3) eV.