Nuclear Magnetic Resonance and Nuclear Quadrupole Resonance Studies of Amorphous Semiconductors

Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements have been performed on two classes of amorphous semiconductors. NMR measurements on hydrogenated amorphous silicon (a-Si:H) were performed using a pulse sequence(known as the Jeener-Broekaert sequence) to study the local hydrogen motion in this sample. Valuable information regarding the trends in local hydrogen motion in a-Si:H with doping levels, temperature and light soaking was obtained from these measurements. These trends in local motion are compared to the measurements of long range hydrogen motion in a-Si:H using the secondary ion mass spectroscopy (SIMS). A phenomenological model is proposed to describe the nature of hydrogen motion as revealed by these experiments. Pulsed NQR measurements of ^{75 }As fibers have been performed at 77K on freshly prepared and aged samples of glassy As_ {2}Se_{3} fibers at three different draw rates (5m/min, 40.7 m/min and 75 m/min). The ^{75}As NQR lineshapes exhibit systematic trends in the linewidths and asymmetries. In addition fibers drawn at the most rapid rate exhibit a second resolved peak in the NQR spectrum that is attributable to the presence of As-As bonds in the nominally stoichiometric glass. NQR lineshapes of the fiber drawn at 40.7 and 75 m/min and annealed, respectively, at 180 and 200^circ C for several hours show that fibers do not undergo complete relaxation to the bulk structure. These results are discussed in the context of structural relaxation processes in As _2Se_3 fiber.