Pulsed electron spin resonance of amorphous and microcrystalline semiconductors

The field sweep spectra of dangling bonds (db) in a-Si:H and a-Ge:H are strongly influenced by the phase memory times T_M, which differ by more than one order of magnitude. A short phase memory time and partial excitation cause a distortion of the field sweep spectra of a-Ge:H. Where two overlapping resonances are present (Ge and Si dangling bond in a-Si:Ge:H and Si db and conduction electrons in #mu#c-Si:H) the resonance with shorter phase memory time is reduced in intensity, with respect to CW-ESR spectra, which are not sensitive to differences in T_M. A separation of the Si and Ge db resonances in a-Si:Ge:H with field-sweep measurements using a long pulse separation time #tau# to exploit the different T_M times and suppress the contribution of the Ge dangling bond was not possible. This may be due to spectral diffusion. For the first time the spin-lattice relaxation times T_1 of the Si and Ge dangling bonds were separated in a-Si:Ge:H. Time domain saturation recovery measurements between 30 K and 300 K show two relaxation times T_1 that are changed with respect to their values in a-Si:H and a-Ge:H and decrease with increasing germanium content, maintaining a difference over the whole detectable alloying and temperature range. The temperature dependence of T_1 is similar to the one found in a-Si:H and a-Ge:H, where it has been connected to the existence of microscopical configurations called two-level systems (TLS). The TLS are coupled to the spin through the spin-orbit coupling of the dangling bond wave function. The change of T_1 with Ge content can be understood through a change of the spin-orbit coupling caused by the atoms back-bonded to the atom carrying the dangling bond. (orig.)140 refs.Available from TIB Hannover: RA 831(3273) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman