Concentration Effect of HF on Energy Band Diagram for n-Si(100)/HF Photoelectrochemical Etching System

Jehng, Wern-Dare; Lin, Jing-Chie; Lee, Sheng-Long

doi:10.1149/1.1858791

Cited by 5 publications

(5 citation statements)

References 34 publications

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“…In BHF solution, we expect the n -type regions of the i–n–i segments to selectively etch, and all of these regions exhibited good etching independent of the SiH 4 partial pressure. The only minor effect was a slight increase in the etch rate with increasing surface Au, which could be attributed to the appearance of a metal-assisted etch mechanism. , However, the relatively minor effect suggests that etching of n -type Si in BHF occurs primarily by the dopant-dependent electrochemical etch mechanism. , Note that in a control study shown in Figure S4, we found that the total reactor pressure in the CVD system played no role in the deposition of Au on the NW surfaces and that instead the SiH 4 partial pressure was the key deterministic factor.…”

Section: Resultsmentioning

confidence: 73%

“…40,41 However, the relatively minor effect suggests that etching of n-type Si in BHF occurs primarily by the dopant-dependent electrochemical etch mechanism. 42,43 Note that in a control study shown in Figure S4, we found that the total reactor pressure in the CVD system played no role in the deposition of Au on the NW surfaces and that instead the SiH 4 partial pressure was the key deterministic factor. The reproducibility of the Au etch stop behavior in KOH solution was confirmed through the growth of intrinsic NWs with the SiH 4 partial pressure periodically modulated between 20 and 200 mTorr, as shown in Figure 4A.…”

Section: Resultsmentioning

confidence: 77%

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Designing Morphology in Epitaxial Silicon Nanowires: The Role of Gold, Surface Chemistry, and Phosphorus Doping

et al. 2017

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Vertically aligned semiconductor nanowires (NWs) have many potential applications for NW-based technologies, ranging from solar cells to intracellular sensors. Aligned NWs can be fabricated by top-down etching of planar wafers or synthesized from the bottom up using the vapor-liquid-solid (VLS) mechanism to induce epitaxial growth on lattice-matched substrates. The VLS process permits the modulation of dopants along the NW growth axis, which if combined with dopant-dependent wet-chemical etching, can be used to encode precise morphology. However, the synthesis of vertical and linear NWs with complex morphology is nontrivial, requiring control over multiple interdependent aspects of the VLS process. Here, we demonstrate sub-10 nm morphology in ⟨111⟩ epitaxial silicon (Si) NWs grown by the VLS mechanism on (111) Si substrates with gold (Au) catalysts. Using silane (SiH), phosphine (PH), and hydrochloric acid (HCl) precursor gases at 480 °C, precise morphology is encoded through abrupt phosphorus (P) dopant transitions, which are found to be less than 5 nm in width. The results highlight three mechanistic attributes of the process. First, NW growth in the ⟨111⟩ direction is found to be unstable at high SiH partial pressures and growth rates unless using HCl, which stabilizes NW growth through chlorination of the NW sidewall. Second, aggregated Au deposited on the NW surface by the VLS catalyst is found to be immobile on the chlorinated surface and to impede selective wet-chemical etching by potassium hydroxide (KOH) solution, preventing the design of precise morphology. Third, the aggregation of Au is found to be strongly dependent on the SiH partial pressure and NW growth rate, and values exceeding ∼100 mTorr and ∼150 nm/min, respectively, are required to minimize Au and thereby enable selective wet-chemical etching. Under optimized growth conditions, we find that abrupt, complex, and arbitrary dopant profiles and morphologies can be encoded in vertical Si NWs, and we expect that a variety of electronic and photonic applications can be realized with these designed nanostructures.

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Section: Resultsmentioning

confidence: 73%

Section: Resultsmentioning

confidence: 77%

Designing Morphology in Epitaxial Silicon Nanowires: The Role of Gold, Surface Chemistry, and Phosphorus Doping

et al. 2017

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“…The space-charge region exists between the electrolyte and silicon due to their different Fermi levels, resulting in the bending of the energy band. 35 Charge transfer also occurs at the interface between the silicon and HF solution. Both types of charge carriers ͓i.e., electrons and holes ͑h + ͔͒ may participate in the charge-transfer process.…”

Section: Discussionmentioning

confidence: 99%

Effect of Ethanol on the Photoelectrochemical Fabrication of Macroporous n-Si(100) in HF Solution

Lin

Lai

Jehng

et al. 2008

J. Electrochem. Soc.

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The effect of ethanol on the photoelectrochemical fabrication of macroporous n-type Si͑100͒ ͑pore diameter Ͼ 50 nm͒ in 2.0 M hydrofluoric acid was investigated. A cross-sectional scanning electron microscope examination revealed the formation of rough bigger pores ͑diameter Ϸ 7-8 m͒ in the absence of ethanol but smooth smaller ones ͑diameter Ϸ 3-4 m͒ in the presence of ethanol when the silicon was etched at 0.250 V ͑vs saturated calomel electrode͒ under 50 W illumination for 3 h. Characteristic electrochemical properties, such as limiting current density ͑i limit ͒, half-wave current density ͑i l/2 ͒, transition potential ͑E trans ͒, and half-wave potential ͑E p/2 ͒ were derived from dc polarization. Electrochemical impedance spectroscopy conducted at E trans and E p/2 was helpful to illustrate the kinetics of the photoelectrochemical reaction. An additional inductive loop in the Nyquist plot occasioned at low frequencies in the presence of ethanol was attributed to the relaxation of the adsorption of ethanol in the pores. Addition of ethanol in the etching solution led to a decrease of contact angle between the solution and the silicon. Wetting behavior of ethanol plays an important role in the formation of smooth and small macropores.

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“…A concerted reaction mechanism would avoid the production of the highly strained intermediate. Other reactions are possible as well, including an acid-catalyzed oxidation reaction , or a photo- or electrochemical reaction. ,, …”

Section: Discussionmentioning

confidence: 99%

“…Other reactions are possible as well, including an acid-catalyzed oxidation reaction 43,44 or a photoor electrochemical reaction. 9,14,45 4.2. Key Spectral Indicators of Si(100) Faceting and Hillock Formation.…”

Section: Discussionmentioning

confidence: 99%

Si(100) Etching in Aqueous Fluoride Solutions: Parallel Etching Reactions Lead to pH-Dependent Nanohillock Formation or Atomically Flat Surfaces

Aldinger

Hines

2012

J. Phys. Chem. C

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A dramatic, pH-dependent change in the steady-state chemical and morphological structure of Si(100) surfaces etched in aqueous fluoride solutions is observed with infrared spectroscopy and scanning tunneling microscopy. Low pH solutions (5 ≤ pH ≤ 7), such as the technologically important buffered oxide etchant (buffered HF), produce rough surfaces covered with nanoscale Si{110}-faceted hillocks. In contrast, higher pH solutions (7.8 ≤ pH ≤ 10), including 40% NH4F (aq.), produce atomically smooth surfaces. The etched surfaces are terminated by a monolayer of H atoms irrespective of pH. The pH-dependent transition is attributed to two competing multistep reaction pathways. At higher pH, the base-catalyzed formation of a surface silanone leads to the production of smooth surfaces. This reaction channel is suppressed at low pH, leading to the formation of {110}-faceted hillocks by a second reaction. The morphological transition is not affected by dissolved O2 in the etchant.

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Concentration Effect of HF on Energy Band Diagram for n-Si(100)/HF Photoelectrochemical Etching System

Cited by 5 publications

References 34 publications

Designing Morphology in Epitaxial Silicon Nanowires: The Role of Gold, Surface Chemistry, and Phosphorus Doping

Designing Morphology in Epitaxial Silicon Nanowires: The Role of Gold, Surface Chemistry, and Phosphorus Doping

Effect of Ethanol on the Photoelectrochemical Fabrication of Macroporous n-Si(100) in HF Solution

Si(100) Etching in Aqueous Fluoride Solutions: Parallel Etching Reactions Lead to pH-Dependent Nanohillock Formation or Atomically Flat Surfaces

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