Seeded growth of bulk ZnO crystals in a horizontal tubular furnace

Abstract

An optimized seeded chemical vapor transport (CVT) method was proposed to grow crack-free bulk ZnO crystals using a conventional horizontal tubular furnace. A silica seed pedestal with a hole in the center is designed to minimize the contact areas between the crystal and the ampoule and thus, suppress generation of thermal stress and cracks. Stable and controlled growth on the seed is achieved. The X-ray rocking curve with a full width at half-maximum (FWHM) of 39 arcsec for the (002) reflection indicates the good crystallinity of the as-grown crystal. Regular micro-growth steps observed by scanning electron microscopy (SEM) indicate that stable growth on the solid–vapor interface is achieved. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) results show that the stoichiometry of the crystal is slightly shifted to Zn-rich and native defects of oxygen vacancies (OV) are formed during growth. Temperature-dependent Hall (TDH) measurement indicates that the as-grown ZnO crystal has a unique electrical property of relatively high carrier mobility (173 cm² V⁻¹ c⁻¹ @ 290 K) with the presence of high carrier concentration (2.22 × 10¹⁷ cm⁻³ @ 290 K), which may be attributed to the high crystallinity of the sample together with the existence of intrinsic donors of oxygen vacancies.