Question

A Si and Ge diode has identical physical dimensions. The band gap in Si is larger than that in Ge. On applying reverse bias,
$\left( A \right)$ The reverse current in Ge is larger than that in Si.
$\left( B \right)$ The reverse current in Ge is smaller than that in Si.
$\left( C \right)$ The reverse current is identical in both the cases.
$\left( D \right)$ None of the above.

Answer 1

Hint: Use the definition in this query that the band gap depends on the forward bias voltage in the p-n junction diode, and is independent of the reverse bias voltage, so use this definition to solve the problem.

Complete step-by-step solution -

As we know Si has a greater band gap in a p-n junction diode as opposed to Ge so Si needs higher forward bias voltage for conduction and Ge requires lower forward bias voltage for conduction, so the band gap depends on the forward bias voltage.
However as we know there is no reverse bias conduction there is just a slight leakage current or reverse saturation current when we apply reverse bias voltage and the sum of reverse saturation current is independent of the applied voltage i.e. reverse saturation current is constant.
Since the physical dimension of Si and Ge is the same, the reverse saturation current is also identical when we apply reverse bias voltage.
So this is the required answer.
Hence option (C) is the correct answer.

Note – Silicon is withstanding very high temperature and current as compare to germanium therefore now a days silicon is preferred over germanium in most of the semiconductors applications such as in diodes, thyristors, IGBT, MOSFET etc. the maximum withstanding temperature of silicon is ${150^o}C$ whereas for germanium it is only up to ${70^o}C$. Generally all of the modern electronic devices are made up of these elements.