Physics · Ch 14 — Semiconductors
Forward biased diode
Forward biased diode
A diode is FORWARD BIASED when its anode (p-side) is connected to the positive terminal of the external voltage source and its cathode (n-side) to the negative terminal. Under forward bias, the width of the depletion region DECREASES, and the p-n junction offers a LOW resistance path, so a comparatively large current is able to flow across the junction (Fig. 14.23).
Fig. 14.24 shows the actual I-V characteristic of a forward biased diode. At first, for small applied voltages, the current stays very low -- most of the applied voltage is still being used up overcoming the internal barrier potential rather than driving current. Then, at a particular voltage, the current begins to rise SHARPLY; the point on the curve where this sharp rise begins is called the KNEE POINT, and the corresponding voltage is called the KNEE VOLTAGE -- about 0.7 V for silicon and about 0.3 V for germanium. …
What this figure shows. A diagram of the p-n junction diode connected in forward bias (positive terminal to the p-side/anode, negative terminal to the n-side/cathode), showing the depletion region drawn distinctly NARROWER than its zero-bias width. The narrowed region is depicted as offering a LOW RESISTANCE path across the junction, consistent with the surrounding text's statement that forward bias reduces the width of the depletion region and allows a high current to f …
What this figure shows. A graph of forward current (vertical axis) against forward voltage (horizontal axis) for a real (non-ideal) diode. The curve starts at the origin and stays very close to the horizontal (voltage) axis -- i.e. current is very small -- for a range of low applied voltages; then, at a particular voltage, the curve bends and rises SHARPLY/steeply upward. The point on the curve where this sharp rise begins is explicitly labelled the 'KNEE POINT', and the voltage on the horizontal axis directly below this knee point is labelled the 'KNEE VOLTAGE' (stated in the text as about 0.7 …