Yutong Guan

Zone Refinement of Germanium Crystals

Purification of commercial germanium with an impurity level of ~1013-14 cm-3 was successfully conducted in two-step zone refining process under an undiluted high-purity hydrogen gas atmosphere. Results for the first step conducted in graphite boats yielded ingots with an impurity level of ~1012 cm-3 near the center of the 60 cm long ingots. These center portions were collected and subsequently zone refined in a high purity quartz boat to reach a purity level of ~1011 cm-3. The best material achieved in a one step process employing a carbon-coated quartz boat yielded material of purity 8×1011 cm-3.

High purity germanium crystal growth at the University of South Dakota

High-purity germanium crystal growth is challenging work, requiring the control of individual crystal properties such as the impurity distribution, the dislocation density, and the crystalline structure. Currently, we grow high-purity germanium crystals by the Czochralski method in our laboratory in order to understand the details of the growing process, especially for large diameter crystals. In this paper, we report the progress of detector-grade germanium crystal growth at the University of South Dakota.

Study on the Properties of High Purity Germanium Crystals

In the crystal growth lab of South Dakota University, we are growing high purity germanium (HPGe) crystals and using the grown crystals to make radiation detectors. As the detector grade HPGe crystals, they have to meet two critical requirements: an impurity level of ~109 to 10 atoms /cm3 and a dislocation density in the range of ~102 to 104 / cm3. In the present work, we have used the following four characterization techniques to investigate the properties of the grown crystals. First of all, an x-ray diffraction method was used to determine crystal orientation. Secondly, the van der Pauw Hall effect measurement was used to measure the electrical properties. Thirdly, a photo-thermal ionization spectroscopy (PTIS) was used to identify what the impurity atoms are in the crystal. Lastly, an optical microscope observation was used to measure dislocation density in the crystal. All of these characterization techniques have provided great helps to our crystal activities.