Maria Kelly

Ion-irradiation control of photoluminescence from porous silicon

Ion irradiation was used to pattern a region of red‐light emitting porous silicon by eliminating visible‐light photoluminescence (PL). The PL peak wavelength is approximately 735 nm and shows little dependence on the excitation‐light wavelength. The ratio of PL intensities for different excitation wavelengths was shown to be proportional to the ratio of the absorption coefficients. Below saturation, the integrated PL intensity increased linearly with excitation‐light power density.

Porous Silicon Formation in N−/N+/N− Doped Structures

This paper examines how dopant profile and anodization conditions affect the formation of buried porous silicon layers in n{sup {minus}}/n{sup +}/n{sup {minus}} doped wafers. Wafers with peak n{sup +} donor concentration {le}10{sup 18}/cm{sup 3} exhibit stray dendritic pores propagating from the n{sup +} layer into the n{sup {minus}} layers. depending on the anodization conditions these larger diameter dendritic pores can even penetrate the entire upper n{sup {minus}} layer, making it unusable for silicon-on-insulator device applications. Lower anodization voltages produce shorter dendrite lengths. Wafers with peak n{sup +} donor concentration {ge}3 {times} 10{sup 18}/cm{sup 3} exhibit negligible stray dendritic pores. In these wafers the buried porous silicon layer is confined only to areas with doping level {ge}1-2 {times} 10{sup 17}/cm{sup 3}. These results should help in optimizing n{sup {minus}}/n{sup +}/n{sup {minus}} doping profiles and anodization conditions for silicon-on-insulator device applications.

Control of photoluminescence from porous silicon

A description of ion-irradiation-induced reduction in the photoluminescence (PL) signal from porous silicon is given and a simple model which is consistent with a nanocrystalline Si structure is presented. Ion irradiation with 250 keV Ne is used to controllably reduce the integrated PL signal by 20% after a fluence of 4*1012 Ne cm-2 and completely eliminate the PL signal after a fluence of 4*1013 Ne cm-2. The use of vacuum and air annealing to recover ion-induced damage is also described, but the high temperatures for annealing cause elimination of the PL signal.

Photoluminescence and passivation of silicon nanostructures

A new method was used to fabricate nanometer‐scale structures in Si for photoluminescence studies. Helium ions were implanted to form a dense subsurface layer of small cavities (1–16 nm diameter). Implanted specimens subjected to annealing in a variety of atmospheres yielded no detectable photoluminescence. However, implantation combined with electrochemical anodization produced a substantial blueshift relative to anodization alone. This blueshift is consistent with the quantum confinement model of photoluminescence in porous silicon.

Multilevel Porous Silicon Formation

Oxidized porous silicon is the basis for one of the frontrunning silicon-on-insulator (SOI) fabrication techniques. Recently, it has also been demonstrated that porous silicon can be metallized to form silicon-on-conductor (SOC) structures. If a method for forming multilevel stacks of porous silicon layers (PSLs) can be developed, it should also be possible to combine the SOI and SOC techniques to form a buried, insulated conductor under single crystal silicon. In this communication, the authors report such a method for multilevel PSL formation.

Microstructure of pores in n+ silicon

Abstract The structure of pores in n−1/n+/n− silicon structures has been studied by cross-section transmission electron microscopy. Under the experimental conditions examined, the pore directions in the n+ layer follow the current path and do not show crystallographic preference. Stray pores were observed in the n− layer and they appear to grow along 〈100〉 directions. By using cross sections transverse to the pore length, we have obtained end-on views that show that the pore walls tend to facet along {111} planes. We have also observed wafer surface faceting on {113} planes as a result of the anodization process.

Hybrid PEDOT/MnOx nanostructured electrocatalysts for oxygen reduction

A series of hybrid poly(3,4-ethylenedioxythiophene)/manganese oxide (PEDOT/MnOx) thin films have been prepared via a stepwise approach: electrodeposition of PEDOT, followed by formation of MnOx particles by a spontaneous redox reaction between PEDOT and KMnO4. Electrocatalytic characterization of the PEDOT/MnOx thin films demonstrates high activity toward the oxygen reduction reaction (ORR), with a shift in intrinsic ORR onset and half-wave potentials by ca. 0.2 V to lower overpotential relative to the PEDOT thin film. The most active PEDOT/MnOx thin film electrocatalyst, P-MnOx-20, demonstrates superior activity relative to the commercial 20% Pt/C catalyst in the half-wave region of the ORR potential window at equal mass loading, with a half-wave potential of 0.83 V (20% Pt/C, 0.81 V) and charge transfer resistance of 479 Ω (20% Pt/C, 862 Ω). The P-MnOx-20 film also demonstrates preference to a pseudo-four electron ORR pathway (n = 3.8) and high specific ORR activity, when considered on both a total mass (−96 mA mgtotal−1; 20% Pt/C: −108 mA mgtotal−1) and metal (or metal oxide) mass basis (−296 mA mgMnOx−1; 20% Pt/C: −540 mA mgPt−1). The P-MnOx-20 film has been identified as the most active PEDOT/ceramic composite electrocatalyst reported to date, which is rationalized by the high surface concentration of Mn(III), strong electronic coupling between PEDOT and MnOx, as well as a high active site density and efficiency achieved by the stepwise electrodeposition-redox approach.

Silicon electrochemistry related to the formation of porous silicon

The authors have examined in detail the electrochemistry of both n- and p-type single-crystal