MICROSCOPIC ORIGIN AND ENERGY-LEVELS OF THE STATES PRODUCED IN A-SI-HBY PHOSPHORUS DOPING

In order to clarify the origin of the phosphorus-related hyperfine-ele ctron-spin-resonance (ESR) signal we study the properties of different ly P-doped amorphous hydrogenated silicon (a-Si:H) prepared at low sub strate temperature (T(s) = 50-degrees-C) and the changes induced by su bsequent annealing at temperatures up to T(A) = 250-degrees-C. In addi tion to the standard ESR and electrical conductivity we use light-indu ced ESR, subgap absorption, and photomodulation spectroscopy to charac terize the samples. We have found that part of the controversy concern ing the origin of the phosphorus hyperfine (hf) signal is related to t he fact that the usual assumptions, namely that the sample is homogene ous, the conduction-band edge energy E(C) is fixed, and only the Fermi level E(f) moves are not satisfied. When the substrate temperature de creases from 250 to 50-degrees-C the hydrogen content and the optical gap of P-doped a-Si:H increases and the anti-Meyer-Neldel behavior ind icates the shift of the transport path (E(C)). Although the total dens ity of deep defects changes only slightly by annealing, their characte r changes substantially. To explain the details of the ESR results het erogeneity given by long-range potential fluctuations must be introduc ed.