Effects of annealing conditions and thickness ratio of Si/Al films on the Hall carrier mobility, Al carrier concentration, and nanovoids formed in the metal-induced Si crystallization of Si/Al/Si/SiO2/glass specimens

In the present study, a-Si/μc-Al/a-Si/SiO2/glass specimens were prepared with various combinations of thicknesses of the μc-Al layer and the two a-Si layers. The effects of μc-Al film thickness, a-Si film thickness, the thickness ratio of Al film to Si films, and the annealing temperature on the metal-induced Si crystallization and void defects formed in the sandwich composite specimens were investigated. A transmission electron microscope (TEM) and an X-ray photoelectron spectroscope (XPS) were used to investigate the diffusion mechanism and efficiency of Si crystallization. When the annealing temperature was sufficiently high, the μc-Al grains diffused into the two adjacent Si layers with a fairly even distribution over the entire sandwich structure. Si crystallization was thus significantly enhanced by the sandwich structure. The Hall carrier mobility of the specimen with a structure of a-Si(500 nm)/μc-Al(50 nm)/a-Si(500 nm) was 80.1 cm2/Vs and the Al carrier concentration was 1.5 × 1018/cm3 at an annealing temperature of 600 °C; no voids were found in the sandwich structure. An increase in the top layer (a-Si) thickness is advantageous for Si crystallization; however, an increase in the third layer (a-Si) thickness degrades Si crystallization. For a given Al film thickness, an excessive increase in the thicknesses of the two a-Si layers degrades Si crystallization even at high annealing temperatures. A thick Al film in combination with two thick a-Si layers leads to a high Hall carrier mobility when the annealing temperature is sufficiently high. An increase in the Si/Al thickness ratio increases the Hall carrier mobility and decreases the Al carrier concentration.