Problem 5
a) Show that green light (λ = 5 x 10-7 m) can excite electronsacross the band gap of silicon (Si).
b) i. Electromagnetic radiation of frequency 3.091 x 1014 Hzilluminates a crystal of germanium (Ge). Calculate the wavelengthphotoemission generated by this interaction. Germanium is anelemental semiconductor with a band gap, Eg, of 0.7 eV. ii. Sketchthe absorption spectrum of germanium, i.e., plot % absorption vs.wavelength, λ.
c) Potassium (K) and beryllium (Be) are metals which exhibitgood electrical conductivity. Explain for both elements the reasonsfor the observed conductivity on the basis of the bandstructure.
d) A pure crystalline material (no impurities or dopants arepresent) appears red in transmitted light. i. Is this material aconductor, semiconductor or insulator? Give the reasons for youranswer . ii. What is the approximate band gap (Eg) for thismaterial in eV?
e) An unknown material is transparent to light of frequencies (ν ) up to 1.3 x 1014 s–1 . Draw a meaningful schematic bandstructure for this material.
