Charge-trapping properties of germanium in crystalline quartz

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Abstract
Germanium impurity in alpha -quartz as a well known deep electron trap and hence makes possible the study of hole trapping processes by EPR techniques. The authors have carried out an EPR study of SiO2:Ge X-irradiated in a microwave cavity at 4K and show that Ge is an amphoteric impurity at low temperatures. In addition to the trapped electron centres they find three EPR spectra, designated H(I), H(II) and H(III), associated with hole trapping by Ge. The spectra H(I) and H(II) are the ground states and an excited state of a hole in a nonbonding 2p orbital in an oxygen ion next to a single substantial germanium ion. This hole centre decays at 35K. The weak spectrum H(III) is due to a hole in a non-bonding 2p orbital in an oxygen ion between two substitution Ge ions and it decays at 58K. The results are compared with the hole-trapping properties of aluminium impurity ions and the question of intrinsic self-trapping of holes in crystalline quartz is discussed.