Study of Non-Aqueous Passivation on GaSb (100) Surfaces
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Study of Non-Aqueous Passivation on GaSb (100) Surfaces Z.Y. Liu and T.F. Kuech Department of Chemical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, 53706 D.A. Saulys Materials Research Science and Engineering Center, University of Wisconsin-Madison, Madison, Wisconsin, 53706 ABSTRACT Due to the high chemical reactivity of GaSb surfaces, many commonly used aqueous sulfide passivation techniques lead to the growth of surface oxides that degrade device performance. We have developed a non-aqueous passivation regime consisting of Na2S/benzene/15-crown5/oxidant. The use of a non-polar, aprotic organic medium required the addition of a specific chelating agent, i.e. a 15-crown-5 ether, to solubilize sodium sulfide, and organic oxidizing agents, such as anthraquinone and benzophenone, to act as electron acceptors. The surface optical and chemical properties of GaSb surfaces after aqueous and non-aqueous sulfide treatments were compared. Non-aqueous passivation resulted in higher PL intensity, lower oxide content, and a less amount of elemental Sb than aqueous passivation.
INTRODUCTION GaSb is an important III-V compound semiconductor for high-speed and optoelectronic device applications, the performance of which are strongly dependent on the chemical and electronic properties of GaSb surfaces or interfaces. However, GaSb is highly chemically reactive, being easily oxidized by atmospheric oxygen with the formation of native surface oxides several nanometers thick.1 An additional consequence of surface oxidation is the formation of elemental antimony at the oxide-GaSb interface, which creates a conductive channel parallel to the interface that leads to high surface leakage current, thus limiting applications.2,3 Various surface passivation methods, including wet and dry chemical processes,4,5,6,7 have been studied in efforts to improve GaSb surface characteristics. Unfortunately, most processing techniques are still water-based and lead to the growth of surface oxides and degrade the structural quality of the surface. Therefore, alternative, non-aqueous, solvents capable of sulfidization are of particular interest for GaSb surface processing. In this work, GaSb surfaces passivated by sodium sulfide in both aqueous and non-aqueous solutions were studied. The non-aqueous passivations were performed in both protic and aprotic organic solvents. Alcohol-based solutions including ethyl, 2-propanol or hexyl alcohols were studied to investigate the effect of solvent on the reactivity of sulfide ions. In addition, a nonaqueous benzene-based sodium sulfide passivation regime was developed to improve the passivation of GaSb surfaces. Chelating agents were employed to solubilize and activate sulfide anions, and organic oxidizing agents were added to the passivation solution to facilitate electron transfer. The optical and chemical characteristics, before and after chemical treatments, were studied by photoluminescence (PL) and x-ray photoemission spectroscopy (XPS). A comparison
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