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Gallium phosphide
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<p>Gallium phosphide (GaP), a <a href="/facts/Phosphide/u5J5Apjs">phosphide</a> of <a href="/facts/Gallium/EucevDs9">gallium</a>, is a <a href="/facts/Compound_semiconductor/RMcsYTWQ">compound</a> <a href="/facts/Semiconductor_material/zFf3mGTE">semiconductor material</a> with an <a href="/facts/Indirect_bandgap/9T1kkc6y">indirect</a> <a href="/facts/Band_gap/IjIeh95l">band gap</a> of 2.24 <a href="/facts/Electronvolt/YMT1fqX9">eV</a> at room temperature. Impure polycrystalline material has the appearance of pale orange or grayish pieces. Undoped single crystals are orange, but strongly doped wafers appear darker due to free-carrier absorption. It is odorless and insoluble in water. </p><p>GaP has a microhardness of 9450 N/mm2, a <a href="/facts/Debye_temperature/Hak5Spp8">Debye temperature</a> of 446 K (173 °C), and a <a href="/facts/Thermal_expansion/BP2vjX0N">thermal expansion</a> coefficient of 5.3 ×10−6 K−1 at room temperature. <a href="/facts/Sulfur/IK0amTfM">Sulfur</a>, <a href="/facts/Silicon/cgWx0hdr">silicon</a> or <a href="/facts/Tellurium/v7QvfIvS">tellurium</a> are used as <a href="/facts/Doping_(semiconductors)/WrGdtWnm">dopants</a> to produce <a href="/facts/N-type_semiconductor/d9GPL5tV">n-type semiconductors</a>. <a href="/facts/Zinc/80b1qgk3">Zinc</a> is used as a dopant for the <a href="/facts/P-type_semiconductor/d9GPL5tV">p-type semiconductor</a>. </p><p>Gallium phosphide has applications in optical systems. Its static <a href="/facts/Dielectric_constant/vnKbPTn1">dielectric constant</a> is 11.1 at room temperature. Its <a href="/facts/Refractive_index/yjkzvgeE">refractive index</a> varies between ~3.2 and 5.0 across the visible range, which is higher than in most other semiconducting materials. In its transparent range, its index is higher than almost any other transparent material, including gemstones such as <a href="/facts/Diamond/IBUdnd1y">diamond</a>, or non-oxide lenses such as <a href="/facts/Zinc_sulfide/K8l5AF3K">zinc sulfide</a>. </p>