EEE436/591 Fall 22, Wang HW5, total: 61+Extra 15 Problem 5. (Extra 15 points) In a pn junction LED, consider a point source in the semiconductor at the junction and assume that the phons are emitted uniformly in all directions. Show that (neglect photon absorption) the external quantum efficiency of the LED is given by (m + na)2 (1 -coste) Where m, and n2 are the refractive index of air and the semiconductor, respectively. And 8, is the critical angle