OPTICAL-PROPERTIES OF AMORPHOUS GALLIUM-ARSENIDE FILMS

Measurements using photothermal deflection spectroscopy (PDS) have bee n performed on samples of amorphous gallium arsenide (a-GaAs) deposite d by rf sputtering. Small quantities of hydrogen (p(H2)=1% P-Ar) induc e changes of the Urbach energy, E(0). This quantity has a linear relat ion with the Tauc optical gap, E(g). The behaviour of E(0) shows a dec rease as a function of the quantity (W/p)(1/2), where W is the dischar ge power and p the pressure in the deposition chamber. E(g) increases with the hydrogen pressure and tends to saturate when p(H2) is greater than 0.1 Pa. E(0) shows exactly the opposite trend. These results are related to structural and morphological data obtained by TEM and THEE D measurements.