Physics · Ch 14 — Semiconductors
A p-n junction diode
A p-n junction diode
A p-n junction fitted with a metallic connector on each side is called a JUNCTION DIODE, or simply a DIODE -- the name reflecting that it is a device with two ('di-') electrodes. Fig. 14.20 shows its circuit symbol: a triangle touching a bar, where the arrow (the triangle's point) indicates the direction of conventional current flow through the device. The P-SIDE of the diode is called the ANODE and the N-SIDE is called the CATHODE.
When a diode is connected across a battery, it can be wired in two different ways -- forward bias or reverse bias (Fig. 14.21) -- and the carriers gain (or fail to gain) additional energy to cross the barrier depending on which way it is biased. Because the barrier potential is affected oppositely by the two connections -- REDUCED under forward bias, INCREASED under reverse bias -- the diode's behaviour in the two cases is starkly different: it carries a comparatively large current, of order a few milliamperes (), when forward biased (since the barrier is both narrower and carriers are pushed toward it), and only a comparatively tiny current, of order a few microamperes (), when reverse biased. Fig. 14.22 depi …
What this figure shows. The standard circuit symbol for a p-n junction diode: a solid filled TRIANGLE with its tip touching a short straight BAR (line) perpendicular to the triangle's axis. The triangle side of the symbol represents the P-SIDE, called the anode; the bar side represents the N-SIDE, called the cathode. The direction the triangle points (from anode toward the bar/cathode) is the direction of the arrow used elsewhere to indicate the direction of conventional current flow per …
What this figure shows. Two simple circuit diagrams, each showing the diode symbol of Fig. 14.20 connected across a battery. In panel (a), the diode's anode (triangle/p-side) is connected toward the battery's positive terminal and the cathode (bar/n-side) toward the negative terminal -- this is the FORWARD BIAS connection. In panel (b), the connection is reversed: the anode is connected toward the battery's negative terminal and the cathode toward the positive terminal -- this is the REVERSE BIAS connection. The two panels are placed side by side purely to contrast the two ways a diode can be wire …
What this figure shows. A single current-versus-voltage graph plotted across both bias directions of a diode, drawn with deliberately different vertical scales on the two sides of the origin to make the asymmetry visible: on the forward-bias (positive voltage) side, the current axis is scaled in MILLIAMPERES and the curve rises to a comparatively large value; on the reverse-bias (negative voltage) side, the current axis is scaled in MICROAMPERES and the curve stays nearly flat at a comparatively minuscule value. The figure's purpose is purely to show, on one combined graph, that forward current is roughly a thousand times or more larger in magnitude than reverse current for …