Aluminum-induced crystallization of hydrogenated amorphous germanium thin films

Abstract

Al-induced crystallization of co sputtered hydrogenated amorphous germanium films, deposited at 220 °C, onto crystalline silicon substrates is investigated by Raman and infrared spectroscopies as a function of the Al concentration (2×10−6<[Al/Ge]<2.5×10−2). Aluminum induces partial crystallization of the films for metal concentrations smaller than ∼1.3 at. %. A sort of explosive crystallization of the films occurs within a narrow Al concentration range (∼1.3<[Al/Ge]<∼1.8 at. %). Raman spectra do not display any crystallization signal for metal concentrations above this narrow range. Data of the extended x-ray absorption fine structure of the coordination and of the local order around gallium, in Ga-doped a-Ge:H, are used to propose an overall picture of the microscopic mechanisms behind these results. A comparative analysis suggests that the crystallization seeds are fourfold-coordinated Al atoms sitting at the center of perfect tetrahedral Ge sites.

Low-temperature growth of polycrystalline Ge thin film on glass by in situ deposition and ex situ solid-phase crystallization for photovoltaic applications

“…To reduce the cost of the material required, poly-crystalline Ge (polyGe) thin films have attracted research interest in recent years. A number of techniques based on physical vapor deposition (PVD) including evaporation [3][4][5], radio-frequency (RF) sputtering [6], sputtering combined with aluminum-induced crystallization [7], sputtering combined with laser crystallization [8,9], and others have been investigated. However, with most of these approaches the film quality reported was poor unless either high substrate temperature (T s ) or an ex situ crystallization process was used.…”

High mobility poly-Ge thin-film transistors fabricated on flexible plastic substrates at temperatures below 130°C

“…16 In the case of MIC, while the basic mechanism is still a subject of study, it has been claimed that compressive stress and lattice shrinkage caused by the introduced metal is the principal factor in Al-induced crystallization of a-Ge. 17 We have speculated that such internal stresses may be reinforced by external mechanical stress to become more effective. In this paper, we report the low-temperature fabrication of depletion mode poly-Ge TFTs on flexible PET substrates at temperatures as low as 130°C.…”

High (1 1 1) orientation poly-Ge film fabricated by Al induced crystallization without the introduction of AlO x interlayer

“…However, the Ge films from these methods tend to have small grain sizes and random orientations. Another, more promising fabrication approach is Al induced crystallization (AIC), which has been widely investigated in the past several decades [6][7][8][9][10]. Using this technique, high (111) orientation and large crystal grains can be acquired, with a lower operational temperature.…”