STRUCTURAL AND LUMINESCENCE STUDIES OF STAIN-ETCHED AND ELECTROCHEMICALLY ETCHED GERMANIUM

Luminescence from stain-etched and electrochemically etched germanium samples was observed in the blue part of the visible spectrum. Althoug h it is weaker than the luminescence of porous silicon, its origin is of scientific interest as a parallel to the luminescence of porous sil icon. Stain-etched germanium was studied in more detail. Under visible laser excitation the luminescence band is located around 525 nm. Anot her luminescence band around 400 nm is observed with UV excitation. Th e luminescence lifetime in the UV-excited band is of the order of 1 ms , compared with about 100 ns in the band excited in the visible. The l uminescence intensity either passes through a maximum or slowly decrea ses as the temperature is increased from 8 to 300 K. This behaviour is similar to that observed in porous silicon. The IR spectra of stain-e tched Ge show the presence of GeO2, -OH groups and water. In the Raman spectra the unmistakable bands of trigonal crystal GeO2 are observed. A band at 760 cm(-1) in the Raman spectra and 752 cm(-1) in the IR sp ectra could be assigned to substoichiometric regions and oxygen- vacan cy complexes in GeO2. The chemical composition of the samples is chara cterized by X-ray photoelectron spectroscopy (XPS) and secondary ion m ass spectrometry ( SIMS). The XP spectra give evidence for GeO2 and Ge O. SIMS data show the presence of both hydrogen and -OH groups. On the basis of these data we propose that the luminescence of stain-etched and electrochemically etched germanium is due to defects in GeO2.