Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers
TL;DR: In this paper, free standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography using electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers.
Abstract: Indirect evidence is presented that free‐standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography. The novel approach uses electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers. Mesoporous Si layers of high porosity exhibit visible (red) photoluminescence at room temperature, observable with the naked eye under <1 mW unfocused (<0.1 W cm−2) green or blue laser line excitation. This is attributed to dramatic two‐dimensional quantum size effects which can produce emission far above the band gap of bulk crystalline Si.
Citations
More filters
TL;DR: The results help to resolve a long standing debate on the origin of visible-NIR PL from Si NWs and allow quantitative analysis of PL from arbitrarily shaped Si NCs.
Abstract: Arrays of vertically aligned single crystalline Si nanowires (NWs) decorated with arbitrarily shaped Si nanocrystals (NCs) have been fabricated by a silver assisted wet chemical etching method. Scanning electron microscopy and transmission electron microscopy are performed to measure the dimensions of the Si NWs as well as the Si NCs. A strong broad band and tunable visible (2.2 eV) to near-infrared (1.5 eV) photoluminescence (PL) is observed from these Si NWs at room temperature (RT). Our studies reveal that the Si NCs are primarily responsible for the 1.5–2.2 eV emission depending on the cross-sectional area of the Si NCs, while the large diameter Si/SiOx NWs yield distinct NIR PL consisting of peaks at 1.07, 1.10 and 1.12 eV. The latter NIR peaks are attributed to TO/LO phonon assisted radiative recombination of free carriers condensed in the electron–hole plasma in etched Si NWs observed at RT for the first time. Since the shape of the Si NCs is arbitrary, an analytical model is proposed to correlate the measured PL peak position with the cross-sectional area (A) of the Si NCs, and the bandgap (Eg) of nanostructured Si varies as Eg = Eg (bulk) + 3.58 A−0.52. Low temperature PL studies reveal the contribution of non-radiative defects in the evolution of PL spectra at different temperatures. The enhancement of PL intensity and red-shift of the PL peak at low temperatures are explained based on the interplay of radiative and non-radiative recombinations at the Si NCs and Si/SiOx interface. Time resolved PL studies reveal bi-exponential decay with size correlated lifetimes in the range of a few microseconds. Our results help to resolve a long standing debate on the origin of visible–NIR PL from Si NWs and allow quantitative analysis of PL from arbitrarily shaped Si NCs.
53 citations
Cites background from "Silicon quantum wire array fabricat..."
...forms of nanostructured Si, such as porous Si [7, 8, 19],...
[...]
TL;DR: In this paper, two distinct photoelectrochemical etching processes are induced by illumination: anisotropic etching, which leads to pore formation and propagation, and isotropic etch, which removes por-Si.
Abstract: The irradiation of n-type Si(111) submerged in HF(aq) with a UV, visible or IR laser can lead to the formation
of photoluminescent porous silicon (por-Si) thin films. We demonstrate that two distinct photoelectrochemical
etching processes are induced by illumination: anisotropic etching, which leads to pore formation and propagation, and isotropic etching, which removes por-Si. As a result, both the solution/por-Si and the
por-Si/c-Si interfaces assume shapes that are determined by the laser intensity profile. A counter reaction
occurs in a spatially separate region of the crystal. A dark reaction between the por-Si and HF(aq) has also
been observed. The photoelectrochemical reaction rates, after an initial increase, approach a constant value. The porous film increases steadily in thickness, while it continues to descend deeper into the crystalline Si.
We discuss a mechanism for the formation and dissolution of the por-Si which emphasizes the effects of quantum confinement within the por-Si.
53 citations
TL;DR: In this paper, the chemical oxidation of hydrogen-terminated silicon surfaces in water was studied in situ with Fourier transform IR spectroscopy in the multiple total internal reflection mode, and it was concluded that reactions involving the oxidation of silicon hydride and the formation of silicon oxide are coupled.
Abstract: The chemical oxidation of hydrogen‐terminated silicon (111) surfaces in water was studied in situ with Fourier transform IR spectroscopy in the multiple total internal reflection mode. On the basis of measurements of the absorbance of the Si‐H and Si‐O‐Si vibrations as a function of time it is concluded that reactions involving the oxidation of silicon hydride and the formation of silicon oxide are coupled. The decrease in the hydride coverage and increase in the oxide coverage are linear functions of ln(t). The time dependence of oxide growth is explained in terms of electrostatic and mechanical changes at the Si/water interface.
53 citations
TL;DR: In this article, a highly porous layer was formed under the radiation spot on the silicon surface, which exhibited strong photoluminescence around 2.0 eV, which was stable to a prolonged continuous illumination of samples.
Abstract: Pulsed radiation of CO2 laser has been used to produce an optical breakdown on a silicon target in atmospheric air. After several breakdown initiations near the threshold of plasma production, a highly porous layer was formed under the radiation spot on the silicon surface. The fabricated layers presented the porosity of 75%–80% and were formed of silicon nanocrystals imbedded in SiO2 matrix. They exhibited strong photoluminescence (PL) around 2.0 eV, which was stable to a prolonged continuous illumination of samples. Possible mechanisms of nanostructure formation and PL origin are discussed.
53 citations
TL;DR: Porous gallium nitride (PGaN) is produced by Pt-assisted electroless etching of GaN Ultrathin Pt films are sputtered onto the surface of the GaN, and etching is carried out in a 1:2:1 or 1: 2:2 solution of CH3OH:HF:H2O2 etching proceeds by first forming a network of small pores, after which ridge structures form, with the porous network in trenches between the ridges As the etch progresses further the sidewalls of the ridge becomes steeper, and
Abstract: Porous gallium nitride (PGaN) is produced by Pt-assisted electroless etching of GaN Ultrathin Pt films are sputtered onto the surface of GaN, and etching is carried out in a 1:2:1 or 1:2:2 solution of CH3OH:HF:H2O2 Etching proceeds by first forming a network of small pores, after which ridge structures form, with the porous network in trenches between the ridges As the etch progresses further the sidewalls of the ridges become steeper, and then the ridges start to disappear Cathodoluminescence (CL) spectroscopy and imaging show the ridges to be optically inactive, suggesting that the ridges might arise from grain boundaries or dislocations present ins the starting GaN material CL emission is confined to the porous areas between the ridges CL properties of the PGaN vary depending on the source of the original, nonporous GaN material Undoped and unintentionally doped hydride vapor phase epitaxy materials produce PGaN which shows only band gap emission at 368 nm before and after etching, whereas PGaN produced from the Si-doped metalorganic chemical vapor deposited material exhibits two blueshifted luminescence bands at 358 and 326 nm The origin of the 358 nm blueshifted emission can plausibly be explained by quantum confinement effects, but the 326 nm band can only be explained by other mechanisms, such as the creation of specific surface states by etching The etched morphology is very similar among the different types of GaN substrates used, however the difference in light emission properties must be ascribed to growth conditions, or to the nature and concentration of the dopants
53 citations
References
More filters
TL;DR: In this article, the properties of electrolyte-semiconductor barriers are described, with emphasis on germanium, and the use of these barriers in localizing electrolytic etching is discussed.
Abstract: Properties of electrolyte-semiconductor barriers are described, with emphasis on germanium. The use of these barriers in localizing electrolytic etching is discussed. Other localization techniques are mentioned. Electrolytes for etching germanium and silicon are given.
1,039 citations
TL;DR: It is found that a standard, widespread, chemical-preparation method for silicon, oxidation followed by an HF etch, results in a surface which from an electronic point of view is remarkably inactive, which has implications for the ultimate efficiency of silicon solar cells.
Abstract: We have found that a standard, widespread, chemical-preparation method for silicon, oxidation followed by an HF etch, results in a surface which from an electronic point of view is remarkably inactive. With preparation in this manner, the surface-recombination velocity on Si111g is only 0.25 cm/sec, which is the lowest value ever reported for any semiconductor. Multiple-internal-reflection infrared spectroscopy shows that the surface appears to be covered by covalent Si-H bonds, leaving virtually no surface dangling bonds to act as recombinatiuon centers. These results have implications for the ultimate efficiency of silicon solar cells.
910 citations
TL;DR: In this paper, multiple internal infrared reflection spectroscopy has been used to identify the chemical nature of chemically oxidized and subsequently HF stripped silicon surfaces, and these very inert surfaces are found to be almost completely covered by atomic hydrogen.
Abstract: Multiple internal infrared reflection spectroscopy has been used to identify the chemical nature of chemically oxidized and subsequently HF stripped silicon surfaces. These very inert surfaces are found to be almost completely covered by atomic hydrogen. Results using polarized radiation on both flat and stepped Si(111) and Si(100) surfaces reveal the presence of many chemisorption sites (hydrides) that indicate that the surfaces are microscopically rough, although locally ordered. In particular, the HF‐prepared Si(100) surface appears to have little in common with the smooth H‐saturated Si(100) surface prepared in ultrahigh vacuum.
588 citations
TL;DR: In this article, the authors measured hydrogen desorption from monohydride and dihydride species on crystalline-silicon surfaces using transmission Fourier-transform infrared (FTIR) spectroscopy.
Abstract: Hydrogen desorption kinetics from monohydride and dihydride species on crystalline-silicon surfaces were measured using transmission Fourier-transform infrared (FTIR) spectroscopy. The FTIR desorption measurements were performed in situ in an ultrahigh-vacuum chamber using high-surface-area porous-silicon samples. The kinetics for hydrogen desorption from the monohydride and dihydride species was monitored using the SiH stretch mode at 2102 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and the ${\mathrm{SiH}}_{2}$ scissors mode at 910 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, respectively. Annealing studies revealed that hydrogen from the ${\mathrm{SiH}}_{2}$ species desorbed between 640 and 700 K, whereas hydrogen from the SiH species desorbed between 720 and 800 K. Isothermal studies revealed second-order hydrogen desorption kinetics for both the monohydride and dihydride surface species. Desorption activation barriers of 65 kcal/mol (2.82 eV) and 43 kcal/mol (1.86 eV) were measured for the monohydride and dihydride species, respectively. These desorption activation barriers yield upper limits of 84.6 kcal/mol (3.67 eV) and 73.6 kcal/mol (3.19 eV) for the Si-H chemical bond energies of the SiH and ${\mathrm{SiH}}_{2}$ surface species.
479 citations