On the nature of electron and hole traps in germanium dioxide thermally grown on germanium

Abstract

In the earlier report (1) we observed negative and positive charging of the oxidized germanium surfaces induced by illumination.In the present work we attempted to get information on the nature of traps in germanium dioxide, thermally grown on germanium, by means of electrophysical methods and the electron spin resonance (ESR). The charging of slow surface states (SS) during the illumination of n-Ge single crystals (8 = 25 to 30ncm), oxidized in wet oxygen, was investigated by the field effect at a large sinusoidal Signal.The illumination was performed by a grating monochromator with a high-pressure xenon lamp. The ESR investigations were made on oxidized germanium powders a s well as on single crystals. The uniform optical excitation of powders was realized by continuous rotation of the ampoules with the powder during illumination.The illumination of single crystals with photons having energy 1.8 eV < h IJ < 1 < 3.3 eV, led to negative SS charging (AQ,), Fig. 1. This charging is caused by the transitions of excited electrons from the valence band of germanium indelocalized o r shallow localized electron states of the amorphous Ge02 film, and followed by trapping of electrons in deep traps in the insulator, Fig. 2, transition 1. On the oxidized germanium powder we observed a single symmetric ESR signal I1 (gl = 2.0025 2 0.0005, A H = 3 to Fig. 1. a) SS charging during illumination for samples heated in vacuum at the temperatures (1) 470 K , (2) 570 K, (3) 670 K. b) The ESR signals 2 physica (a)