Chemical analysis of a Si crystal reveals Ga at a level of 3•10^{−2} atomic percent. Assuming that the concentration of thermally excited charge carriers from the Si matrix is negligible, what is the density of free charge carriers/cm^{3} in this Si crystal?

**Answer**

Atomic weight of Si = 28

Density of Si = 2.33 g/cm^{3} = 5.01•10^{22} atoms/cm^{3}

charge carriers / cm^{3} = 5.01•10^{22} × 3•10^{−4} = 1.503•10^{19}