Substitutional and interstitial doping of amorphous silicon nitride

Abstract

Doped films of amorphous silicon nitride have been prepared by the glowdischarge technique over a wide range of ammonia-silane mixtures. Phosphorus-and boron-doped specimens were produced by admixing measured amounts of phosphine or diborane during deposition. Interstitial doping of specimens was attempted with sodium by ion-beam implantation, and with lithium by evaporation and in-diffusion. The electrical conductivity and the optical gap of these specimens have been determined as a function of the volume ratio of ammonia to silane. All four dopants raise the conductivity of low-nitrogen-content specimens to about l o w 2 R -* cm-' at room temperature, without changing the optical gap. With increasing nitrogen content the effect of phosphorus, boron and sodium doping decreases rapidly. In contrast, incorporation of lithium significantly increases the room-temperature conductivity of even high-nitrogen-content films. By careful control of the preparation conditions, near-stoichiometric, optically transparent specimens have been produced in which the room-temperature conductivity has been increased by fourteen orders of magnitude through lithium doping.

Paramagnetic Point Defects in Amorphous Silicon Dioxide and Amorphous Silicon Nitride Thin Films: II .

“…Figure 1 is purely schematic in nature; the above quantities do not vary linearly with x. As x is increased, the optical bandgap opens up from Eg = 1.8 eV in a-Si:H to about 5.5 eV in the N-rich compositions, i.e., a-SiNL6:H. The change in the optical bandgap with film stoichiometry has been explained at length by others (33,38) and will not be considered here. The bandgap is defined here as the photon energy at which the optical absorption is =104 cm-1.…”

“…Figure 1 schematically illustrates how the nature of the Si dangling-bond is believed to vary with film stoichiometry (x). Besides changes in the zero-crossing g value and the peak-to-peak ESR linewidth, the optical bandgap, dielectric constant, and the refractive index of the a-SiN=:H also change quite appreciably with film stoichiometry (24,33,(38)(39)(40)(41)(42)(43). Figure 1 is purely schematic in nature; the above quantities do not vary linearly with x.…”

Light-induced metastable changes in amorphous silicon nitride

“…Moreover, doping of semiconductors having -U defects should not cause a change in conductivity because the Fermi energy remains pinned between the K -and K' energy levels until the dopant concentration exceeds the K-centre concentration. Dunnett, LeComber and Spear (1988) reported, however, a significant increase in the 300 K conductivity of nitrogen-rich a-SiN, : H films with lithium doping. Unfortunately they did not report whether the lithium concentration incorporated was larger than 5 x 1018cm-3, the concentration of K defects in undoped silicon nitride.…”