TheAlgorithms/Python · error · ValueError

Donor concentration should be positive

Error message

Donor concentration should be positive

What it means

Raised by builtin_voltage() (electronics/builtin_voltage.py:42) when donor_conc <= 0. The function computes a PN-junction built-in voltage V_bi = kT/q * ln(Nd*Na/ni^2), which is only physically meaningful for positive doping concentrations. This is the first check in an ordered elif chain, so it fires before the acceptor/intrinsic checks.

Source

Thrown at electronics/builtin_voltage.py:42

    Traceback (most recent call last):
      ...
    ValueError: Acceptor concentration should be positive
    >>> builtin_voltage(donor_conc=1000, acceptor_conc=1000, intrinsic_conc=0)
    Traceback (most recent call last):
      ...
    ValueError: Intrinsic concentration should be positive
    >>> builtin_voltage(donor_conc=1000, acceptor_conc=3000, intrinsic_conc=2000)
    Traceback (most recent call last):
      ...
    ValueError: Donor concentration should be greater than intrinsic concentration
    >>> builtin_voltage(donor_conc=3000, acceptor_conc=1000, intrinsic_conc=2000)
    Traceback (most recent call last):
      ...
    ValueError: Acceptor concentration should be greater than intrinsic concentration
    """

    if donor_conc <= 0:
        raise ValueError("Donor concentration should be positive")
    elif acceptor_conc <= 0:
        raise ValueError("Acceptor concentration should be positive")
    elif intrinsic_conc <= 0:
        raise ValueError("Intrinsic concentration should be positive")
    elif donor_conc <= intrinsic_conc:
        raise ValueError(
            "Donor concentration should be greater than intrinsic concentration"
        )
    elif acceptor_conc <= intrinsic_conc:
        raise ValueError(
            "Acceptor concentration should be greater than intrinsic concentration"
        )
    else:
        return (
            Boltzmann
            * T
            * log((donor_conc * acceptor_conc) / intrinsic_conc**2)
            / physical_constants["electron volt"][0]

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass positive physical values, typically ~1e15 to 1e19 per cm^3 for silicon.
2. Check the value's origin: if it comes from a parser, treat 0/None as missing data and fail loudly upstream.
3. Verify unit conversions use float math (1e6 factors, not int).

Example fix

# before
builtin_voltage(donor_conc=0, acceptor_conc=1e16, intrinsic_conc=1e10)  # ValueError

# after
builtin_voltage(donor_conc=1e16, acceptor_conc=1e15, intrinsic_conc=1e10)

def positive(x: float) -> bool:
    return isinstance(x, (int, float)) and x > 0

def positive_float(x: object) -> TypeGuard[float]:
    return isinstance(x, (int, float)) and not isinstance(x, bool) and x > 0

try:
    builtin_voltage(nd, na, ni)
except ValueError as e:
    if 'positive' in str(e):
        raise ValueError(f'Bad doping input: nd={nd}, na={na}, ni={ni}') from e
    raise

When it happens

Trigger: Calling builtin_voltage(donor_conc=0, ...), with a negative donor concentration, or with 0.0 floats. Only fires when donor_conc is the first failing value; a negative acceptor_conc with positive donor_conc raises the acceptor error instead.

Common situations: Default-initializing concentration variables to 0; unit-conversion bugs (e.g. cm^-3 to m^-3 producing 0 via integer division); reading missing values from a datasheet column that default to 0.

Related errors

• Acceptor concentration should be positive
• Intrinsic concentration should be positive
• Capacitor at index {index} has a negative value!
• Capacitor at index {index} has a negative or zero value!
• Expected a_coeffs to have {self.order + 1} elements for {sel

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/a1139940d74fd72b. Report an issue: GitHub.