Research Highlights

1. Redefinition of the Photoelectrochemical Etching Regime

Instead of relying on high-energy electrochemical or thermal-assisted processes, this research introduces a low-energy photoelectrochemical etching framework, enabling deterministic control over pore nucleation and growth dynamics.

Distinct advances include:

Suppression of excessive hole injection to stabilize pore evolution
Achievement of wafer-scale uniform nanoporous layers
Simultaneous realization of P-type and N-type porous silicon architectures
Significantly improved process reproducibility compared to conventional anodization

Figure 1. Integration of Nanoporous Silicon Devices with a Copper-Plated PCB Platform.

Figure 2. Schematic illustration of the low-energy photoelectrochemical etching strategy for nanoporous silicon fabrication, highlighting the suppression of excessive hole injection and the controlled formation of quantum-confined nanostructures.

2. Quantum-Confinement-Governed Luminescence Engineering

By tailoring nanocrystal dimensions within the porous matrix, the optical emission behavior is governed predominantly by quantum confinement rather than surface defect states.

Key findings:

Tunable visible emission achieved through pore size modulation
Laser-assisted etching enhances carrier generation efficiency
Clear correlation established between excitation wavelength, confinement scale, and radiative recombination
Substantial enhancement in photoluminescence stability and intensity

Figure 3. PL image of the nanoporous silicon layer prepared under optimized photoelectrochemical conditions, showing a uniform pore distribution and a well-controlled nanostructure suitable for quantum confinement.

Figure 4. Voltage- and illumination-dependent photoluminescence behavior of the nanoporous silicon structure, indicating effective carrier modulation and optoelectronic tunability.

3. Nanoporous Silicon P–N Junction Devices

Building upon the controlled doping and etching strategy, this work demonstrates electrically stable nanoporous silicon P–N junctions, exhibiting both rectifying behavior and electroluminescent response.

Device-level significance:

Reduced forward-bias operation voltage
Suppressed interface recombination losses
Improved electroluminescence uniformity
Viable pathway toward silicon-based light-emitting devices

Figure 5. Structural and optoelectronic characteristics of the P–N nanoporous silicon device fabricated via low-temperature liquid-phase bonding, confirming good interfacial integrity and stable light emission.

Figure 6. A large-area P-type porous silicon layer exhibiting red photoluminescence (PL) with minimal structural damage results in good luminescence uniformity.

4. Low-Temperature Liquid-Phase Bonding for Nanostructured Silicon

To address the thermal fragility of nanoporous silicon, a liquid-phase APTES-mediated bonding technique is implemented, enabling strong interfacial adhesion without compromising pore morphology.

Advantages:

Bonding achieved under low thermal budget
Preservation of nanoscale porosity
Reduced interfacial void formation
Enhanced integration compatibility with silicon photonic platforms

Figure 7. shows the FTIR spectra of the P–N nanoporous silicon samples before and after the liquid-phase bonding process.

A pronounced absorption band observed at approximately 1000–1100 cm⁻¹ is attributed to the Si–O–Si stretching vibration, indicating the formation of siloxane bonds at the bonding interface. This feature confirms successful interfacial condensation reactions between surface silanol groups during the bonding process. The absorption peaks located around 1400–1500 cm⁻¹ are assigned to –CH₂ bending vibrations, while the bands near 2850–2950 cm⁻¹ correspond to –CH₂ stretching modes, demonstrating the presence of organic linker molecules on the porous silicon surface. In addition, distinct peaks appearing at approximately 1550–1650 cm⁻¹ and 3200–3400 cm⁻¹ are associated with –NH₂ and –NH stretching vibrations, respectively. These nitrogen-related functional groups originate from amine-terminated molecules and play a critical role in promoting chemical bonding and mechanical stability at the P–N interface. The coexistence of Si–O–Si, –CH₂, and –NH vibrational modes provides strong evidence that the P–N nanoporous silicon layers are bonded through a combination of inorganic siloxane networks and organic molecular linkers, resulting in a chemically robust and electrically functional bonded interface.

Figure 8. Porous silicon diode device, side FE-SEM image.

Impact and Application Potential

The proposed processing paradigm provides a scalable and CMOS-compatible route for integrating light-emitting, sensing, and photonic functionalities into silicon-based systems, with implications for on-chip optoelectronics, quantum photonic devices, and next-generation integrated sensors.

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