Silicon is a hard, brittle crystalline solid and a key semiconductor material used in electronics and photovoltaics; it is the second most abundant element in Earth’s crust.
Silicon has the ground-state configuration \([Ne]3s^2\,3p^2\). It commonly exhibits oxidation states +4 (e.g., SiO2, SiCl4) and +2 in some compounds; in alloys and Zintl phases it can show negative formal states.
Silicon crystallizes in the diamond cubic lattice with covalent \(sp^3\) bonding. It has an indirect band gap of about \(E_g \approx 1.12\,\text{eV}\) at 300 K. This moderate gap allows thermal excitation of carriers at room temperature, enabling diode and transistor action while keeping leakage manageable.
Doping introduces shallow energy levels:
Carrier concentration is set by dopant density \(N_D\) or \(N_A\). The mass action law holds: \(np = n_i^2\), where \(n_i\) is the intrinsic carrier concentration.
Thermally grown SiO2 forms a high-quality, stable, insulating oxide directly on Si with excellent interface properties. It is the gate dielectric in classic MOSFETs and provides surface passivation and isolation. Native oxidation (simplified):
\(\mathrm{Si + O_2 \rightarrow SiO_2}\)
Metallurgical-grade Si is produced by carbothermic reduction in an electric arc furnace:
\(\mathrm{SiO_2(s) + 2\,C(s) \rightarrow Si(l) + 2\,CO(g)}\)
For semiconductor-grade purity, it’s converted to volatile SiCl4 or trichlorosilane (HSiCl3) and chemically vapor deposited (Siemens process), followed by zone refining and crystal growth (Czochralski or float-zone).
Si and SiO2 are resistant to many mineral acids. Hydrofluoric acid attacks SiO2, forming volatile silicon tetrafluoride:
\(\mathrm{SiO_2 + 4\,HF \rightarrow SiF_4\,(g) + 2\,H_2O}\)
Buffered HF solutions are standard for oxide removal in microfabrication. Extreme caution: HF is highly toxic and requires specialized PPE.
Silicones (polysiloxanes) are inorganic–organic polymers with Si–O–Si backbones and organic side groups (e.g., –CH3):
\(\mathrm{[-Si(R)_2\!{-}O-]_n}\)
They offer thermal stability, flexibility, and hydrophobicity—used in sealants, lubricants, medical devices, and electronics encapsulants.
In a p–n junction, photons with \(h\nu \ge E_g\) create electron–hole pairs. The built-in electric field separates carriers, generating current. Photon energy relates to wavelength by \(E = \dfrac{hc}{\lambda}\); for Si \(E_g\approx 1.12\,\text{eV}\), the cutoff is \(\lambda_c \approx 1100\,\text{nm}\).
The Metal–Oxide–Semiconductor Field-Effect Transistor controls channel conductivity via an electric field across a thin oxide (SiO2 or high-k). Applying gate voltage modulates inversion charge, enabling amplification and switching—fundamental to digital ICs and CPUs.
Yes. Respirable crystalline silica can cause silicosis and other lung diseases. Use dust control, local exhaust, wet methods, and appropriate respirators when cutting/grinding materials containing silica (e.g., concrete, stone, ceramics).