(1).in case of germanium the valence eleectrons are in 4th orbit but in case of silicon the valence electrons are in 3rd orbit.scince the valence electrons in germanium are in higher energy level than in silicon so these valence electrons require smaller amount of additional energy to escape from germanium than silicon,,but this property of germanium makes it more unstable at high temperature,thos is the basi reason why silicon is used widely,,,,,,,,,,,

Silicon diodes have a greater ease of processing, lower cost, greater power handling, less leakage and more stable temperature characteris diode is a semiconductor device which allows current to flow through it in only one direction. Although a transistor is also a semiconductor device, it does not operate the way a diode does. A diode is specifically made to allow current to flow through it in only one direction.
Some ways in which the diode can be used are listed here.
A diode can be used as a rectifier that converts AC (Alternating Current) to DC (Direct Current) for a power supply device.
Diodes can be used to separate the signal from radio frequencies.
Diodes can be used as an on/off switch that controls current.
This symbol is used to indicate a diode in a circuit diagram.

The meaning of the symbol is (Anode)(Cathode).
Current flows from the anode side to the cathode side.

Although all diodes operate with the same general principle, there are different types suited to ...more