  The COBRA collaboration investigates 0{\nu}\beta\beta-decays (neutrinoless
double beta-decays). Therefore, a demonstrator setup using coplanar-grid CdZnTe
detectors is operated at the LNGS underground laboratory. In this work, the
demonstrator was commissioned and completed, which is discussed extensively.
The demonstrator works reliably and collects low-background physics data. One
result of the analysis of the data is that surface events are the dominating
background component. To better understand and possibly discriminate this
background, surface events were studied in detail. This was done mainly using
laboratory measurements. For a better interpretation of these measurements,
simulations of particle trajectories and ranges were done. The surface
sensitivity tests showed large differences between the individual detectors.
Often, a dead-layer was determined, especially at the surfaces where the
non-collecting anode (NCA) is the outermost anode rail. Due to this, the
sensitivity of the surfaces where the collecting anode (CA) is adjacent was
typically about a factor of three larger than the NCA sensitivity. A comparison
of the pulse shape analysis methods LSE and A/E was done. Laboratory
measurements indicate, that the latter performs better. Alpha scanning
measurements were done to spatially investigate the surface sensitivity.
Plausible variations were measured. However, no hints were found how to improve
the surface event recognition. The instrumentation of the guard ring, which
surrounds the anode structure, was tested and improved the surface event
discrimination significantly. The fraction of surviving alpha events was at a
per-mill level. Important steps for a future large-scale COBRA experiment are
discussed briefly, mainly the use of an integrated read-out system. Overall,
the results indicate a large potential in background reduction for the COBRA
experiment.
