Characterization of Thermally Evaporated Ag-Ge-S Thin Films
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1072-G03-21
Characterization of Thermally Evaporated Ag-Ge-S Thin Films Fei Wang1,2, William Porter Dunn2, Mukul Jain2, Carter De Leo2, Nicholas Vicker2, Richard Savage2, Xiaomin Jin2, Sergey Mamedov3, and Punit Boolchand4 1 California State University at Long Beach, Long Beach, CA, 90840 2 California Polytechnic State University, San Luis Obispo, CA, 93407 3 Horiba Jobin Yvon Inc, Edison, NJ, 08820 4 University of Cincinnati, Cincinnati, OH, 45221 ABSTRACT Thin films of ternary (GeS3)1-xAgx glasses (x=0.1 and 0.2) are characterized in this studied as potential media for information storage. The films are deposited in a vacuum thermal evaporator at 3 different evaporation angles (0o, 30o and 45o) and are examined by Raman spectroscopy. The Raman spectra from both normally and obliquely deposited thin film samples reveal Ge-S CS modes (~340cm-1) , Ge-S ES (~360cm-1) modes and thiogermanate modes Q1~Q3 (390cm-1~437cm-1). In addition, the spectra contain sharp peaks due to sulfur rings (S8), which are observed at 218cm-1 and 470cm-1. The Raman line-shapes are qualitatively consistent with those observed in bulk glasses. However, the sharp peaks due to sulfur rings were not observed in bulk glasses. By comparing the CS modes at three angles, we observe that normally deposited (0 degree) thin films show a red-shift towards the center and a broadening in width. Film thickness of normally deposited films are significantly less when compared against obliquely deposited films. INTRODUCTION Chalcogenide glasses are extensively used in rewritable non-volatile memory applications. In general, information storage devices based on chalcogenide materials could be categorized into two types. One is information storage based on the phase change of chalcogenide materials between an amorphous state and a crystalline state [1]. This technique is widely used in rewritable optical data recording (e.g. RW-DVD discs). Materials used as active recording layers for this category are Sb-Te containing alloys, with the most widely used material being the Ge-Sb-Te (GST) system [2-4]. The other type of information storage mechanism is relatively new. It is known as Programmable Metallization Cell memory (PMC). This type of memory device controls the amount of metal dopants in a solid state electrolyte using electrochemical methods [5-6]. Therefore, one can control the resistivity of the solid state electrolyte to achieve the data recording purpose. Materials used as active recording films for this category are metal doped chacogenides, such as Ag-Se, Ag-S[7], Ag-Ge-Se [5-6], Ag-Ge-S [8], Cu-S [9]etc. PMC, compared to phase change memory, has the advantages in terms of short recording time, low recording power as well as better scaling capability [5-6]. Silver doped germanium sulfide (Ag-Ge-S) films have demonstrated PMC behaviour and several successful devices have been fabricated. [7,8] To further understand these films, one needs to have a thorough knowledge of the characteristics of film, such as its molecular structure, stress and process re
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