Semiconductors and pn Junction Diodes

A region depleted of mobile charge carriers formed at the interface between p-type and n-type semiconductors.

The potential difference that naturally exists across the p-n junction due to the diffusion of charge carriers.

Electrons move from the n-type side to the p-type side and holes move from the p-type side to the n-type side.

The thickness of the space charge region, typically measured in microns.

The process of forming a p-n junction by joining p-type and n-type semiconductors.

The barrier potential is created by the electric field that forms across the space charge region. It prevents further diffusion of charge carriers.

The energy difference between the Fermi levels of the p-type and n-type materials in a p-n junction.

In a p-n junction, the Fermi levels on both sides align due to charge movement across the junction.

In an n-type semiconductor, the Fermi level (EF) is close to the conduction band edge (ECn).

In a p-type semiconductor, the Fermi level (EF) is close to the valence band edge (EVp).

The conduction band edge of an n-type semiconductor won't be at the same level as that of a p-type semiconductor in a p-n junction.

It's the difference in energy levels between the conduction band edge of the n-type semiconductor and the valence band edge of the p-type semiconductor.

Shows the relationship between the Fermi level and the conduction band edge for an n-type semiconductor.

Shows the relationship between the Fermi level and the valence band edge for a p-type semiconductor.

The product of electron concentration (n) and hole concentration (p) is constant and equal to the square of intrinsic carrier concentration (ni).

The intrinsic carrier concentration (ni) is a measure of the number of free electrons and holes in a pure semiconductor.

The width of the depletion region in a p-n junction is directly proportional to the square root of the barrier potential. This means that as the barrier potential increases, the width of the depletion region also increases.

When a reverse bias voltage is applied to a p-n junction, the width of the depletion region increases. This is because the reverse bias voltage increases the potential difference across the junction, which in turn increases the electric field strength.

The depletion region is assumed to be located entirely on the p-side of the junction. This is because the density of holes (the majority carriers on the p-side) is much higher than the density of electrons (the minority carriers on the p-side).

The relationship between potential and charge density in a p-n junction is described by Poisson's equation. This equation can be integrated twice to obtain an expression for the potential as a function of distance.

The diode equivalent circuit is a simplified representation of the real device, used for analysis and design. Different models exist, with varying levels of accuracy: Piece-wise Linear, Simplified, and Ideal. The Piece-wise Linear model represents the diode's behavior with a linear slope when it's ON and a high resistance when it's OFF.

The reverse saturation current of a diode approximately doubles for every 10 degrees Celsius increase in temperature. This means that as temperature rises, the diode conducts more current even without a significant change in voltage.

The change in voltage (dV) needed to maintain a constant current (I) in a diode due to a change in temperature (dT) is approximately -2.5 mV/°C. This means that the voltage across the diode needs to be adjusted to compensate for temperature fluctuations.

The cut-in voltage (or barrier voltage) of a germanium diode is approximately 0.3V, while for a silicon diode it's around 0.7V. This voltage represents the minimum voltage needed to start conducting current through the diode.

The barrier voltage of a diode (both germanium and silicon) decreases by approximately 2mV for every 1°C increase in temperature. This decrease is due to the temperature dependence of the material's properties.

The diode's static resistance (also known as DC resistance) is the resistance measured at a particular DC operating point on the diode's characteristic curve. It is calculated by dividing the DC voltage across the diode (VD) by the DC current flowing through it (ID).

The dynamic resistance of a diode is the resistance measured at a specific point on the diode's characteristic curve, considering the change in voltage (dV) and the change in current (dI). It's calculated as the ratio of dV to dI.

The maximum temperature limit for germanium diodes is around 75°C, while for silicon diodes it's around 175°C. Exceeding these limits can damage the diode or significantly alter its characteristics.

The effect of temperature on the diode characteristic curve is shown in the figure. The curve shifts to the left and downward as temperature increases, indicating that more current flows at the same voltage compared to lower temperatures.

The formula 𝐼02 = 𝐼01 × 2 𝑇2 −𝑇1 /10 describes how the reverse saturation current (𝐼0) changes with temperature. It shows that the saturation current doubles for every 10°C increase in temperature.

The DC resistance of a diode at the knee and below is greater than the resistance at the vertical rise section of the characteristic curve. The resistance in the reverse-bias region is very high.

The charge stored in a diode varies directly with the applied forward bias voltage, similar to a capacitor. The rate of change of charge with respect to the applied forward voltage defines the diode's capacitance.

The diffusion capacitance, denoted as Cd, is the capacitance associated with the accumulation of charge carriers in the depletion region of a diode due to the diffusion of charge carriers under forward bias.

The rate of change of charge Q with respect to the applied forward voltage V is represented as dQ/dV. This represents the capacitance of the diode due to charge accumulation.

The average lifetime of a charge carrier in a semiconductor material, represented by the symbol τ, is the average time that a charge carrier (electron or hole) exists before recombining with another carrier.

The current flowing through a diode due to the movement of charge carriers across the p-n junction. It is denoted by the symbol I and is related to the charge Q and the average lifetime τ of the carriers: I = Q/τ.

The current that flows through a diode when it is reverse biased. It is represented by the symbol I0 and is typically very small.

The diode current equation relates the current flowing through a diode to the applied voltage and the diode properties. It is expressed as I = I0 * exp(V/ηVT) - I0.

The thermal voltage VT is a constant in semiconductor physics that reflects the thermal energy of charge carriers. It is calculated as VT = kT/q, where k is Boltzmann's constant, T is the absolute temperature, and q is the elementary charge.

The ideality factor η accounts for deviations from the ideal behavior of a diode. It is typically a value between 1 and 2, depending on the physical characteristics of the diode. It appears in the diode current equation to refine the relationship between current and voltage.

The transition capacitance, denoted as CT, is a capacitance associated with the depletion region of a p-n junction diode. It's dependent on the applied reverse bias voltage and the characteristics of the junction.