Microstructural Evolution During the Epitaxial Growth of Ag/InP (100)
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primarily from the goal of understanding the formation of electrical contacts to devices, e.g. Ag or
Au on InP [1]. Several studies have addressed the initial stages of growth of metals (e.g. Ag) on 'clean' semiconductors (particularly Si and GaAs) using techniques such as low energy electron microscopy [2], scanning tunneling microscopy [3] and scanning electron microscopy techniques [4]. In particular, studies have concentrated on metal/semiconductor systems that are non-reactive. Also, for growth of metals on compound semiconductors, the (110) cleavage surface has been the most popular even though the (100) surfaces are perhaps more technologically important. Recently, there have been reports of several novel phenomena observed in metal/semiconductor epitaxy. Some examples include: the formation of self-assembled wires of NiAl on AlAs(100) [5], shape transformation of Ag islands on Si(100) [2] and the observation of quantum-size effects from Ag/GaAs( 110) [6]. The nanostructural development in these epitaxial systems is closely related to the growth mechanism, and may have potential applications in quantum-structures. We present in-situ studies of the growth of a reactive system Ag on InP (100), with a focus on the microstructural evolution of Ag islands from the early stages of nucleation to early stages of coalescence. The experiments were performed in-situ in an ultra-high vacuum -scanning transmission electron microscope (UHV-STEM) with extensive sample preparation facilities [7, 8]. The samples were characterized in-situ using a high spatial resolution secondary electron (SE) imaging [7, 8] and ex-situ using transmission electron microscopy (TEM). EXPERIMENTAL PROCEDURE Vicinal Fe -doped InP wafers, nominally 2' misoriented towards the nearest < 110> zone (steps along ) were used in the experiments. The samples used had either a 0.5g InP epilayer grown using metal-organic chemical vapor deposition (henceforth called type A) or used 59 Mat. Res. Soc. Symp. Proc. Vol. 355 01995 Materials Research Society
without any surface treatments (type B samples ). Each experiment consisted of the following steps. Samples were first loaded into the UHV-STEM preparation chamber through an airlock and heated for about 90 min at -450"C to desorb the native oxide on the surface [9]. The sample was then transferred to the microscope column for observation without breaking vacuum. The sample cleanliness was determined by observing the surface using SE imaging. The surface with partially sublimed surface oxide was easily visible in samples that were heated below 400*C. Those heated above - 450*C appeared clean. The sample was subsequently transferred back into the preparation chamber for Ag deposition. Silver was deposited from a water cooled Knudsen source with the sample maintained at a specific temperature. After the deposition, the sample was transferred back into the column for observation. Further Ag depositions were performed onto the same sample and the SE images acquired digitally. More details on the experimental pr
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