Growth of heavily-doped Germanium single crystals for mid-Infrared applications

In the growth of germanium (Ge) single crystals by Czochralski (Cz) method, a novel gas-phase doping procedure has been suggested to obtain heavily doped, both n-type (phosphorous) and p-type (boron) semiconducting crystals. The crystals were grown using the so-called mini-Cz technique and the pulled crystals are characterized for their structural and electrical properties. A narrow full width at half maximum (FWHM) of the X-ray diffraction rocking curves obtained for both symmetric (4 0 0) reflection (14 arcsec) and asymmetric (3 1 1) reflection (11 arcsec) indicate good crystalline quality. In addition, the grown crystals have a low dislocation density (etch pit density of approximate to 10(4) cm(-2)) without hot-zone optimization. Doping concentrations of up to 3 x 10(18) cm(-3) have been obtained so far, which implies that gas-phase doping is a viable route and may solve some of the conventional doping issues when using solids as dopants in the Cz melt. We also report here high doping of antimony (Sb) using a solid dopant source. Non-flat solid-liquid interface of the Sb-doped crystals during the growth process, as characterized by the typical ring structure of the growth striations, has been seen in lateral photovoltage scanning (LPS) measurements.