A pn junction diode and a Schottky diode each have...

A pn junction diode and a Schottky diode each have cross-sectional areas of $A=8 \times 10^{-4} \mathrm{~cm}^{2}$. The reverse saturation current densities at $T=300 \mathrm{~K}$ for the pn junction diode and Schottky diode are $8 \times 10^{-13} \mathrm{~A} / \mathrm{cm}^{2}$ and $6 \times 10^{-9} \mathrm{~A} / \mathrm{cm}^{2}$, respectively. Determine the required forward-bias voltage in each diode to yields currents of (a) $150 \mu \mathrm{A},(b) 700 \mu \mathrm{A}$, and (c) $1.2 \mathrm{~mA}$.

Key Concepts

Diode Equation

This fundamental relationship, often called the Shockley diode equation, describes how the current through a diode depends exponentially on the applied voltage, the reverse saturation current, and the thermal voltage. It is expressed as I = I?[exp(V/(nV?)) – 1], where I is the diode current, I? is the reverse saturation current, V is the applied voltage, n is the ideality factor, and V? is the thermal voltage.

Reverse Saturation Current

The reverse saturation current is the small leakage current that flows through a diode when it is reverse-biased. It is highly dependent on temperature and the physical properties of the diode material and structure, and it plays a crucial role in determining the forward-bias voltage required for a given current.

Thermal Voltage

Thermal voltage (V?) is a parameter that represents the thermal energy of charge carriers in a semiconductor, typically around 26 mV at room temperature. It is defined as V? = kT/q, where k is Boltzmann’s constant, T is the absolute temperature, and q is the charge of an electron, and it appears in the exponent of the diode equation.

Forward-Bias Voltage

Forward-bias voltage refers to the voltage applied to a diode in the direction that allows current to flow easily. In this condition, the barrier at the junction is reduced, leading to an exponential increase in current as described by the diode equation.

pn Junction Diode

A pn junction diode is formed by the junction of p-type and n-type semiconductor materials. It exhibits a characteristic exponential current-voltage behavior, with relatively low reverse saturation current and a distinct threshold voltage for conduction.

Schottky Diode

A Schottky diode is formed by a metal-semiconductor junction rather than a p–n junction. It typically has a lower forward voltage drop and a higher reverse saturation current compared to a pn junction diode, due to its different charge carrier transport mechanisms.

Current Density and Device Area

The current density is the current per unit area, and the total current through a diode is the product of this current density and the diode's cross-sectional area. This relationship is important when scaling the reverse saturation current from a density value to the actual current used in the diode equation.

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