Gallium arsenide has relative permittivity ϵr=12.9 and a conduction electron effective mass of 0.067m.
((a)) Estimate a donor's binding energy and orbit radius in gallium arsenide, using the same hydrogen-scaling model as for phosphorus in silicon.
((b)) Gallium arsenide holds 4.42×1022 atoms per cm3. Estimate how many atoms the donor orbit encloses, and say whether treating the crystal as a uniform dielectric is still reasonable at this size.