TABLE OF CONTENTS This is essentially the same thing as the tunnel diode, only the doping is a little lighter. It is called a backward diode because everything is the other way round. It has low impedance in the reverse direction and high impedance in the forward direction, as shown in Fig. 9.27.
The secret of the device is that the doping is just that much lighter (than that of the tunnel diode) as to line up the band edges (the top of the valence band on the p-side to coincide with the bottom of the conduction band on the n-side) at zero bias. Hence, for a forward bias there is no tunnelling, just the 'normal' flow, which is very small. In the reverse direction, however, a large tunnelling current may flow.
The backward diode is a very efficient rectifier (of the order of one to a thousand) for low voltages. For higher voltages, of course, the 'forward' current may become significant.
