Electrical characterization of process induced defects in germanium

Abstract

The origins and identity of process induced defects in semiconductors has proven to be a particularly difficult problem to solve. Germanium, a semiconductor once again at the forefront of device technology, has played a leading role in advancing semiconductor physics and now, through the use of readily available ultra-pure germanium, allows us to interrogate a crystal structure electrically with a sensitivity that is unsurpassed. This thesis presents a number of recently discovered process induced electron and hole traps, the most noteworthy of which is E0.31. This point defect with an energy level of 0.31 eV below the conduction band modified the properties of germanium rendering it immune to the introduction of electron beam deposition (EBD) induced defects. E0.31 was introduced during etching with a subthreshold energy argon plasma, was annealed to a level below 1011 cm−3, the detection limit of our system, but could then not be reintroduced in the sample. This result suggests that plasma etching modified an existing defect that did not have a deep level in the bandgap. Investigations into the conditions experienced by substrates during EBD before the deposition, termed electron beam exposure (EBE) herein, introduced defects not seen after EBD with only the E-center common to both processes. The substantial differences in defect type and concentration noted between these processes has not been explained as the role of the growing metal film remains unclear in EBD defect introduction. Inserting mechanical shields to block energetic particles created in the electron-beam path from colliding with samples resulted in Schottky barrier diodes being manufactured with EBD defect concentrations that were too low to measure using deep level transient spectroscopy. This observation confirms that energetic particles created in collisions with 10 keV electrons were responsible for EBD defects and not high energy electrons, as previously reported.