Photoconductivity and thermally stimulated current in CaGa2S4single crystals doped with Eu2+and Ce3+

✍ Scribed by Hidaka, Chiharu ;Hiraguri, Kazuma ;Takizawa, Takeo

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 307 KB
• Volume: 205
• Category: Article
• ISSN: 0031-8965
• DOI: 10.1002/pssa.200824140

✦ Synopsis

Abstract

Photoconductivity (PC) measurements are carried out on single crystals of CaGa~2~S~4~ doped with Ce^3+^ and Eu^2+^ at room temperature and at about 30 K. Low temperature PC spectra can only be measured for Ce doped samples but not for Eu ones owing to too high resistivity. Based on the data obtained, the energy level scheme of Ce^3+^ ions is discussed in reference to the optical band edge.

Single crystals of CaGa~2~S~4~ are grown by codoping Ce^3+^ with Na^+^ ions to observe the charge compensation effect expected to occur under the substitution of Ca^2+^ ions by Ce^3+^ ions. Their electrical resistivity is reduced about two orders in magnitude from ca. 10^13^ Ω cm to ca. 10^11^ Ω cm without much change in PC spectra, suggesting a mere decrease in scattering centers for carriers. From the variation in DC resistivity with time, it is expected that many carrier traps may exist in the compounds. To clarify those trap levels the thermally stimulated current (TSC) is measured using samples with different Ce^3+^ concentrations. From the analysis of TSC spectra, 6 traps with different depths have been retrieved. We have also found traps which may have repelling potential barriers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)