The origin of defects induced in ultra-pure germanium by Electron Beam Deposition

TL;DR

This study investigates the origin of electron-beam induced defects in ultra-pure germanium, revealing that energetic particles from collisions are the primary cause, and demonstrates methods to reduce defect formation during deposition.

Contribution

It identifies collision-induced energetic particles as the main source of defects in EBD and shows how shielding and vacuum improvements can significantly lower defect concentrations.

Findings

Defects mainly caused by collision products, not high-energy electrons or photons.

Shielding and vacuum improvements reduce defect concentrations below 10^11 cm^-3.

Energy packets as small as 2 eV can cause lattice changes deep within the material.

Abstract

The creation of point defects in the crystal lattices of various semiconductors by subthreshold events has been reported on by a number of groups. These observations have been made in great detail using sensitive electrical techniques but there is still much that needs to be clarified. Experiments using Ge and Si were performed that demonstrate that energetic particles, the products of collisions in the electron beam, were responsible for the majority of electron-beam deposition (EBD) induced defects in a two-step energy transfer process. Lowering the number of collisions of these energetic particles with the semiconductor during metal deposition was accomplished using a combination of static shields and superior vacuum resulting in devices with defect concentrations lower than $ 10^{11}\,$cm$^{-3}$, the measurement limit of our deep level transient spectroscopy (DLTS) system. High energy electrons and photons that samples are typically exposed to were not influenced by the shields as most of these particles originate at the metal target thus eliminating these particles as possible damage causing agents. It remains unclear how packets of energy that can sometimes be as small of 2eV travel up to a $\mu$m into the material while still retaining enough energy, that is, in the order of 1eV, to cause changes in the crystal. The manipulation of this defect causing phenomenon may hold the key to developing defect free material for future applications.