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Germanium dioxide was used as the germanium source for the preparation and analysis of semiconductor germanium films on solid and liquid electrodes in an aqueous solution system. XRD and Raman spectra showed that the samples prepared on Cu plates were all amorphous germanium and the deposition temperature and time had a significant effect on the final formation thickness of the germanium films, while a too high deposition temperature may cause cracks in the germanium films during growth. In contrast,crystalline germanium films can be prepared on liquid electrodes at lower temperatures(<90 °C ), and the optimal quality of crystalline germanium films was achieved when the deposition temperature was 80 °C. In addition, XRD results showed that the growth of germanium on the (220) and (311) crystal planes was hindered when the concentration of the germanium source was low(<70 mmol/L). [ABSTRACT FROM AUTHOR]

The fabrication of high-quality crystalline germanium thin films (GeTF) on an amorphous SiO layer is crucial for the realization of high performance-, low cost III-V solar cells used in many applications. Herein, we report the growth of a high-quality crystalline GeTF on SiO/Si substrates using an ultra-vacuum chemical vapor deposition (UHV-CVD) method. GeTF was grown on the SiO layer using a two-step growth and multi-annealing processes. The fabrication method involved the deposition of a 1 seeding layer, annealing, and deposition of a 2 main layer followed by three times of cyclic annealing. The crystallization of the seeding layer having a thickness of less than 10 nm could be ascribed to the evolution of polycrystalline structures in the main layer. The cyclic annealing performed after the deposition of the main layer is also found to be crucial for the formation of single crystalline, high-quality Ge films on SiO substrates with <311> direction. The cyclic annealing results in a further reduction of the defects, thereby threading dislocations significantly to a density of ~ 5.311 × 10 cm. Electrical measurements using the van der Pauw method revealed that the GeTF exhibits p-type characteristics and a high mobility of 360.10 cm/Vs at room temperature. [ABSTRACT FROM AUTHOR]

Crystallization of germanium (Ge) thin films was investigated by depositing Ge on glass and silicon substrates using electron beam (e-Beam) evaporation. The hole carrier concentration in Ge thin films deposited on glass substrates was found to decrease slightly with increasing annealing temperature, whereas its Hall mobility was found to increase monotonically. For all crystallized Ge thin films herein reported, the conductivity was found to be dominated by holes (p-type). This characteristic was then exploited to fabricate p-Ge/n-Si heterojunction diodes on n-type silicon substrates, which were then investigated by analysis of their current–voltage and capacitance–voltage characteristics. It was found that increasing annealing temperatures lead to significant improvements in on/off ratio and ideality factor, as well as increased built-in voltage. After crystallization of the top p-Ge layer through annealing at 600 °C, the devices indicated an on/off ratio of 10 6 , an ideality factor of 1.25 and a built-in potential of 0.58 eV. The improvement in device performance is correlated with the crystallization of the Ge thin films, as confirmed by Hall effect and X-ray diffraction measurement, which indicated increases in hole mobility and improved solid-phase crystallization with increases in annealing temperature. The photoresponse of the devices was characterized employing a two-dimensional mapping approach, which provides insight into the optical generation and recombination processes at the Ge/Si heterojunction. The results herein presented indicate that thermally crystallized Ge thin films may be of significant promise for electronic and optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Arming metasurface with active materials furnishes a feasible solution to dynamically control over terahertz (THz) waves, which is extremely significant for the realization of upcoming sixth generation telecommunications. However, the present active materials are mainly limited to single external driving field, hindering the capability of metasurface for flexible manipulation of THz waves. Besides, less attention has been paid to the energy question how to significantly reduce the pump threshold for achieving the desired function. Here, a germanium (Ge) hybrid Fano metasurface under dual-stimulus control is experimentally demonstrated. Photoexcitation of Ge thin film enables 100% modulation depth of Fano resonance and ultrafast switching time within 10 ps. By adding current-bias, the pump threshold to modulate the metasurface is greatly reduced from 1600 to 200 µJ cm -2 . Different from the optical modulation independent of film thickness, it is found that the current function is in proportion with the thickness of Ge thin film. Moreover, it is demonstrated that compared to the single optical-stimulus, the THz amplitude modulation is increased by 56.3% under dual-stimulus function. This work naturally improves the flexibility and practicality of Ge-based metadevice and inspires more innovations to boost the development of switchable sensing, lasing spacer, and nonlinear systems., (© 2021 Wiley-VCH GmbH.)