Effects of Ge on Material and Electrical Properties of Polycrystalline Si1 − x Ge x for Thin‐Film Transistors

Abstract

Films deposited by very low pressure chemical vapor deposition (VLPCVD), with and without plasma enhancement, and by low‐pressure CVD (LPCVD) were studied to explore the effects of Ge on various properties of films. As the Ge content increases, growth rates increase for thermal and plasma‐deposited polycrystalline and amorphous films. The transition temperature for poly‐to‐amorphous deposition is lower, and the crystallization of amorphous films is faster. Enlarged grain sizes are achieved with Ge in films grown thermally, with plasma enhancement, and by solid‐phase crystallization, with grain sizes as large as 1.3 μm in films of 1000 Å thickness. Increased n‐type and p‐type Hall mobilities and decreased p‐type resistivities are achieved as functions of Ge content in films with . The Hall mobility in an n‐type film is 50 cm²/V‐s, the highest value reported to date for materials. thin‐film transistors (TFTs) have been fabricated and evaluated, leading to a proposal of a poly‐Si‐capped TFT structure.