n-Type Polycrystalline Germanium Layers Formed by Impurity- Doped Solid-Phase Growth

The carrier mobility of polycrystalline Ge thin-film transistors has significantly improved in recent years, raising hopes for the realization of next-generation electronic devices. Here, we adapted advanced solid-phase crystallization, which achieved the highest hole mobility of the polycrystalline semiconductor layer, to Ge layers doped with n-type impurities (P, As, and Sb). The type and amount of dopants had marked effects on the growth morphology and electrical properties of the Ge layers because they altered the activation energies in crystal growth, dopant activation rates, and grain boundary properties. In particular, P doping was effective in increasing the grain size (25 mu m) and lowering the grain boundary barrier height (20 meV), which improved the electron concentration (8.0 x 1018 cm-3) and electron mobility (380 cm2 V-1 s-1) in n-type polycrystalline Ge layers. The electron mobility is greater than that of most semiconductor layers synthesized at low temperatures (<= 500 degrees C) on insulators, and this will pave the way for advanced electronic devices, such as multifunctional displays and three-dimensional large-scale integrated circuits.