Markku Tammenmaa

Zinc chalcogenide thin films grown by the atomic layer epitaxy technique using zinc acetate as source material

Abstract Anhydrous zinc acetate (Zn(CH 3 COO) 2 ) was found to be a suitable source material for growing thin films by the atomic layer epitaxy method. The growth of both ZnS and ZnO thin films with good reproducibility and uniform thickness from Zn(CH 3 COO) 2 and H 2 S or H 2 O respectively was demonstrated. ZnS thin films showed excellent crystallinity and a high orientation of the growth direction. The ZnO thin films were mainly amorphous and the growth rate was approximately one-fifth of that found for ZnS growth. Some experiments were also carried out to dope the ZnS films with manganese and terbium, resulting in yellow and green luminescence respectively.

Alkaline earth sulfide thin films grown by atomic layer epitaxy

Abstract Alkaline earth sulfide (CaS, SrS, BaS) thin films have been grown by the atomic layer epitaxy method on glass substrates. Starting materials were the 2,2,6,6-tetramethyl-3,5-heptanedionato (thd) chelates of the alkaline earth metals and hydrogen sulfide. The growth rate was reasonable (0.3-0.4 A/cycle) and according to the X-ray diffraction patterns and Auger spectra the films were polycrystalline and chemically pure. All films were slightly oriented but each towards different directions: CaS along (220), SrS along (111) and BaS along (200).

Zinc sulphide thin films doped with rare earth ions

Zinc sulphide thin films doped with trivalent rare earths (cerium, europium, terbium, thulium) have been grown by the atomic layer epitaxy (ALE) method using hydrogen sulphide and zinc chloride or acetate as starting materials and rare earth β-diketonates as dopants. The films were characterized by X-ray diffraction and X-ray fluorescence techniques and their photoluminescence was studied. It is possible by ALE to grow thin films of good quality and to control the distribution of the rare earth ions in the ZnS matrix. The most intense luminescence was obtained with Ce3+ and Tb3+. Europium also gave a distinct luminescence while that of thulium remained poor. The band gap of ZnS was apparent in the excitation spectra and its energy depended on the crystal structure of the zinc sulphide thin film (cubic or hexagonal).

Materials for electroluminescent thin films

Recent work on luminescent materials suitable for high field AC operated thin film devices is reviewed. Yellow emitting ZnS:Mn2+, still the best EL material known, is used in commercial flat panels. The need for full-color devices has led to the development of lanthanoid doped zinc and alkaline earth sulfide thin films emitting blue, green and red light. Of these new phosphors, the green emitting ZnS:TbF3 is closest to commercial application.

Characterization of thin-film electroluminescent structures by SIMS and other analytical techniques

ZusammenfassungNeuentwickelte epitaktische Abscheideverfahren („Atomic Layer Epitaxy — ALE“) ermöglichen die Herstellung von elektroluminescierenden Dünnfilmstrukturen hoher Qualität, welche für verschiedene elektronische Displays eingesetzt werden können. Neben der lichtemittierenden Schicht — üblicherweise Mangan-dotiertes ZnS — enthalten derartige Strukturen einige andere Komponenten wie Al2O3- oder Indium-Zinn-Oxid-(ITO)-Schichten. Die Gesamtdicke aller Schichten eines Displays beträgt ca. 2 μm. Für die Bestimmung der Aktivatorkonzentration (Mn) sowie von Terbium und der Schichtdicke von ZnS wurde eine röntgenfluorescenzanalytische Routinemethode ausgearbeitet. Die Sekundär-Ionen-Massenspektrometrie (SIMS) ermöglicht die Charakterisierung der Schichtstrukturen und der Verunreinigungen in einzelnen Schichten. Dies gestattet insbesondere die Untersuchung der Verteilung und Diffusion des wichtigen Spurenelementes Natrium.SummaryThe recently developed Atomic Layer Epitaxy (ALE) method produces good quality electroluminescent thin-film structures which can be used in various display applications. Besides the light emitting layer which is usually ZnS: Mn2+, the structures contain several other components such as aluminium oxide and indium-tin oxide layers; the total thickness is around 2 μm. It was found that XRF provides a convenient way for the determination of activator concentrations and film thicknesses while SIMS can be used for the determination of depth profiles in a wide concentration range. A rapid and accurate method for the routine determination of Mn2+ and Tb3+ in ZnS by XRF is described and the use of SIMS for the study of sodium distribution and diffusion is discussed.

Simultaneous determination of the cerium content and the thickness of cerium-activated alkaline earth metal sulfide films by x-ray fluorescence spectrometry

Abstract The cerium content and the film thickness of cerium-activated alkaline earth metal sulfide films were determined simultaneously. The cerium determination was calibrated by using standard solutions on filter paper. Film thickness was determined by comparing the S Kα intensities with those in zinc sulfide standards. The detection limit for cerium was estimated to be 0.1 μg cm−2.