A sharp optical absorption edge has been found at about 0.5 eV for amorphous Ge on a quartz substrate. The edge is comparable in sharpness with the direct edge of crystalline Ge. No evidence for tailing of the band edges into the forbidden band or for a high density of states in the forbidden band is found by these optical measurements. A new density determination gives a value of 4.54± 0.14 g/${\mathrm{cm}}^3$.

• Received 24 March 1969

DOI:https://doi.org/10.1103/PhysRevLett.22.1058