Idealfaktor

Idealfaktor, or ideality factor, is a parameter used in semiconductor physics to describe deviations of a p–n junction diode from the ideal diode law. In the Shockley diode equation, the current I as a function of the applied voltage V is I = I_S (exp(V/(nV_T)) - 1), where I_S is the reverse saturation current, V_T = kT/q is the thermal voltage, and n is the ideal factor. The factor n is dimensionless and summarizes non-ideal effects such as recombination in the depletion region, tunneling, and series resistance, which cause the diode to deviate from the ideal exponential behavior. In German-language sources, "Idealfaktor" is the standard term for this parameter.

Typical values and interpretation: The ideality factor is near 1 for devices where diffusion currents dominate, approaching 2 when recombination in the depletion region plays a larger role. For silicon diodes, n commonly lies between 1 and 2, depending on temperature, current, and device quality. Values near 2 indicate a stronger influence of non-ideal processes such as recombination, while very high values may signal high injection, significant series resistance, or trap-assisted currents. The ideality factor can vary with temperature and operating point and is not a fixed constant for a given device.

Measurement and usage: Engineers determine n by fitting forward I-V measurements to the diode equation or by using device models in circuit simulators such as SPICE. The parameter is often reported in datasheets for completeness and is used to predict diode behavior under different temperatures and currents.