What is the difference between arsenic doping and phosphorus doping in single crystal Silicon

Both are N-type semiconductors, but what's the difference between arsenic and phosphorus doping in single-crystal silicon? In single-crystal silicon, arsenic (As) and phosphorus (P) are both commonly used N-type dopants (pentavalent elements that provide free electrons). However, due to differences in atomic structure, physical properties, and processing characteristics, their doping effects and application scenarios differ significantly.

I. Atomic Structure and Lattice Effects

Atomic Radius and Lattice Distortion

Phosphorus (P): With an atomic radius of approximately 1.06 Å, slightly smaller than silicon (1.11 Å), doping with As results in less distortion of the silicon lattice, lower stress, and better material stability.

Arsenic (As): With an atomic radius of approximately 1.19 Å, larger than silicon, doping with As results in greater lattice distortion, potentially introducing more defects and affecting carrier mobility.

In their position within silicon, both dopants primarily act as substitutional dopants (replacing silicon atoms). However, due to its larger radius, arsenic has a poorer lattice match with silicon, potentially leading to an increase in localized defects.

II. Differences in Electrical Properties

Donor Energy Level and Ionization Energy

Phosphorus (P): The donor energy level is approximately 0.044 eV from the conduction band bottom, resulting in a low ionization energy. At room temperature, it is almost completely ionized, and the carrier (electron) concentration is close to the doping concentration.

Arsenic (As): The donor energy level is approximately 0.049 eV from the conduction band bottom, resulting in a slightly higher ionization energy. At low temperatures, it is incompletely ionized, resulting in a carrier concentration slightly lower than the doping concentration. At high temperatures (e.g., above 300 K), the ionization efficiency approaches that of phosphorus.

Carrier Mobility

Phosphorus-doped silicon has less lattice distortion and higher electron mobility (approximately 1350 cm²/(V・s)).

Arsenic doping results in a slightly lower electron mobility (approximately 1300 cm²/(V・s)) due to the lattice distortion and more defects, but the difference decreases at high doping concentrations.

III. Diffusion and Processing Characteristics

Diffusion Coefficient

Phosphorus (P): Its diffusion coefficient in silicon is relatively large (e.g., approximately 1e-13 cm²/s at 1100°C). Its diffusion rate is fast at high temperatures, making it suitable for forming deep junctions (such as the emitter of a bipolar transistor).

Arsenic (As): Its diffusion coefficient is relatively small (approximately 1e-14 cm²/s at 1100°C). Its diffusion rate is slow, making it suitable for forming shallow junctions (such as the source/drain region of a MOSFET and ultra-shallow junction devices).

Solid Solubility

Phosphorus (P): Its maximum solid solubility in silicon is approximately 1×10²¹ atoms/cm³.

Arsenic (As): Its solid solubility is even higher, approximately 2.2×10²¹ atoms/cm³. This allows for higher doping concentrations and is suitable for ohmic contact layers requiring high conductivity.

Ion Implantation Characteristics

The atomic mass of arsenic (74.92 u) is much greater than that of phosphorus (30.97 u). Ion implantation allows for a shorter range and shallower implantation depth, making it suitable for precise control of shallow junction depths. Phosphorus, on the other hand, requires deeper implantation depths and, due to its larger diffusion coefficient, is more difficult to control.

The key differences between arsenic and phosphorus as N-type dopants in single-crystal silicon can be summarized as follows: Phosphorus is suitable for deep junctions, medium-to-high concentration doping, simple processing, and high mobility; while arsenic is suitable for shallow junctions, high concentration doping, precise junction depth control, but with significant lattice effects. In practical applications, the appropriate dopant must be selected based on the device structure (e.g., junction depth and concentration requirements), process conditions (e.g., diffusion/implantation parameters), and performance targets (e.g., mobility and conductivity).

Semicorex offers high-quality single crystal Silicon products in semiconductor. If you have any inquiries or need additional details, please don't hesitate to get in touch with us.

Contact phone # +86-13567891907

Email: sales@semicorex.com