Hydrogen passivation effects on polycrystalline germanium thin films

Abstract The performance of polycrystalline Ge thin films, anticipated for application in advanced electronic and optical devices, has markedly improved in recent years. However, the high density of acceptor defects in Ge complicates Fermi level control, impeding device applications. This study explores defect passivation by incorporating hydrogen atoms into recently developed high-quality polycrystalline Ge thin films. Hydrogen introduced to Ge through plasma processes forms Ge-H bonds in large-grained Ge layers, in contrast to conventional small-grained Ge layers where this bonding does not occur. Increasing Ge-H bonding correlates with a reduction in defect-induced hole concentration from 10 ¹⁷ cm ⁻³ to the order of 10 ¹⁵ cm ⁻³ , representing the lowest reported hole concentration for polycrystalline Ge layers. Low-temperature annealing after hydrogenation further decreases the hole concentration while improving the hole mobility. These findings indicate that hydrogen atoms in Ge passivate both acceptor defects and grain boundary carrier traps. The resulting Ge layer achieves high hole mobility (170 cm ² V ⁻¹ s ⁻¹ ) and low hole concentration (4 × 10 ¹⁴ cm ⁻³ ), an accomplishment unattainable with conventional polycrystalline group IV semiconductor thin films, paving the way for implementing polycrystalline Ge-based thin films in semiconductor devices.