Create a graph showing the current-voltage relationship of a PN junction diode, including both forward and reverse bias regions.

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This graph shows the current-voltage characteristic of a PN junction diode. The x-axis represents voltage in volts, and the y-axis represents current in milliamperes. In the reverse bias region, where voltage is negative, only a very small negative current flows. In the forward bias region, when voltage exceeds the knee voltage of approximately 0.7 volts, the current increases exponentially with small increases in voltage. Let's examine the forward bias region in more detail. The current through a diode follows the Shockley equation, where current increases exponentially with voltage. Different semiconductor materials have different threshold voltages. Silicon diodes, shown in blue, have a threshold or knee voltage of approximately 0.7 volts. Germanium diodes, shown in green, have a lower threshold of about 0.3 volts. Once the voltage exceeds these thresholds, the current increases rapidly with small voltage changes. Now let's examine the reverse bias region of the diode I-V characteristic. When a negative voltage is applied to the diode, only a very small leakage current flows. This current is typically in the nanoampere to microampere range and remains nearly constant as the reverse voltage increases. However, at a sufficiently high reverse voltage, known as the breakdown voltage, the current suddenly increases dramatically. This breakdown occurs at around 50 to several hundred volts for typical silicon diodes, though we've shown it at -8 volts in our simplified diagram. Temperature has a significant effect on diode characteristics. As temperature increases, the forward voltage drop decreases by approximately 2 millivolts per degree Celsius for silicon diodes. This is shown by the red curve, representing a diode at 75 degrees Celsius, where the knee voltage shifts left. Conversely, at lower temperatures, shown by the green curve at negative 25 degrees Celsius, the knee voltage increases. In the reverse bias region, the leakage current approximately doubles for every 10 degree increase in temperature. This is why the red curve shows higher reverse current, while the green curve shows lower reverse current. These temperature effects are important considerations in circuit design. To summarize what we've learned about PN junction diode I-V characteristics: First, diodes conduct current primarily in one direction, which is the forward bias direction. In forward bias, current increases exponentially once the voltage exceeds the knee voltage, which is approximately 0.7 volts for silicon and 0.3 volts for germanium diodes. In reverse bias, only a very small leakage current flows until the breakdown voltage is reached. Temperature significantly affects diode behavior, decreasing the forward voltage drop and increasing the reverse leakage current as temperature rises. The entire I-V relationship is described mathematically by the Shockley diode equation. Understanding these characteristics is essential for designing and analyzing electronic circuits that use diodes.