Density of gap states in hydrogenated amorphous silicon
Amorphous silicon hydride films have been grown by an improved r.f. sputtering method in a hydrogen-argon atmosphere. Deposition parameters such as substrate temperature, gas flow rate, r.f. power, and argon partial pressure were kept constant, while hydrogen partial pressure was varied. The infrared vibrational modes, optical absorption, conductivity, and density of gap states from the Fermi level upward toward the conduction band edge of these films have been studied as a function of hydrogen content of the films. The density of states distribution of the films has been deduced from Space Charge Limited Current measurements with an Au/a-Si:H Schottky diode structure. Samples with ('(TURN)) 15.5% at. H have densities of states of 3 x 10('14) states/cm('3) eV and show large majority carrier mobility-lifetime products of 10('-5) cm('2)V('-1). An Au/a-Si:H diode which is nearly ideal (diode quality factor = 1.05) was obtained for a-Si:H films with hydrogen concentrations of about 16 at. %. The experi- mental results indicate that a high quality a-Si:H material with a low;density of states of 3 x 10('14) states/cm('3)eV can be obtained by r.f. sputtering method; ('1)DOE Report IS-T-1163. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.