Suppose that in a p-type semiconductor the ionized acceptor concentration at x = x1, is na – = n1 << nv and falls off exponentially to a value na - = n2 >> n1 at x = x2. What is the build-in electric field in the interval (x1, x2)? Give numerical values for n1/n2 = 103 and x2 – x1 = 10-5 cm. Assume T = 300K. Impurity distributions such as this occur in the base region of many n-p-n transistors. The built-in field aids in driving the injected electrons across the base.