Germanium arsenide iodide: A clathrate semiconductor

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Abstract
Germanium forms two semiconducting arsenides: the monoclinic germanium monoarsenide, GeAs, and the orthorhombic germanium diarsenide, GeAs2. When the reaction of germanium, arsenic, and iodine in a sealed tube was used for the crystal growth of GeAs and GeAs2, cubic crystals were also obtained. These crystals have been identified by electron microprobe analysis and x-ray and neutron diffraction studies to be germanium arsenide iodide, (Ge38As8)+8⋅8 I−, a clathrate semiconductor. The germanium arsenide iodide cyrstals are n type with a room temperature resistivity of about 1 ohm-cm and carrier concentration of about 5×1017 cm−3. The Hall mobilities are 10–20 cm2/V-sec, relatively independent of temperature. The energy gap estimated from the resistivity-temperature relation is approximately 0.9 eV.