A Si sample is uniformly doped with phosphorus at 5 E 16 cm^-3. We make a p-n junction by implanting boron atoms into the surface layer. The implanted depth is 0.15 µm. What should the surface concentration of the boron implant be in order to obtain a p-n junction with equal concentrations of holes in the p-region and electrons in the n-region? Assume the 100% implant activation. HINT. The surface concentration is the number of atoms per unit surface area. For example, if the sample has impurity concentration of Nd=1E16 cm^-3 and is d=0.1 cm thick, then the surface concentration of impurity would be Nd*d = 1E16*0.1 = 1e15 cm^-2 (note the units for the surface concentration). B) What is the built-in voltage at room temperature?