Free-standing thin film Ge single crystals grown by plasma-enhanced chemical vapor deposition

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Abstract
Single crystal Ge films (∼10 μm) have been epitaxially grown on polished (100) NaCl substrates at 450 °C by plasma enhanced chemical vapor deposition (PECVD). Upon cooling, the films were separated from the substrate by differential shear stress which left handleable free-standing films of Ge. Growths were achieved by nucleating at minimum plasma power (∼10 W) for very short intervals and then raising the power to 65 W to increase the growth rate to approximately 10 μm/h. Substrate exposure to the plasma at too high a power for too long a time was found to sputter and erode the surface, thus substantially degrading the nucleation process and the ultimate growths. The free-standing films were visually specular and exhibited a high degree of crystalline order when examined by x-ray diffraction. Auger electron spectroscopy (AES) and energy dispersive analysis of x rays (EDAX) showed no detectable bulk contamination. The films were found to be p type with a carrier concentration of approximately 3×1016 cm−3, a resistivity of 0.11 Ω cm, and a Hall hole mobility of 1820 cm2 V−1 s−1 at room temperature.