Difference between direct band gap and indirect band gap semiconductors

Hello friends,
 
Let us understand the type of the semiconductors based on the type of the recombination.There are two types of semiconductors based on the type of recombination. They are      

1. Direct band gap semiconductors .
2. Indirect band gap semiconductors.

Direct band gap semiconductor:

        These are compound type of semiconductors such as GaAs, which have their conduction band minima directly above the valence band maxima, in the diagram the valence band and conduction band are shown with multiple lines which are various energy levels as these are bands of energy. The energy band structure is shown below:

       In the figure the electrons from conduction band directly recombine with the holes in the valence band and during the process of recombination and during the process energy is released in the form of light. This is helpful in construction of LED's, The dotted red line indicates the recombination process.The properties of the direct band gap recombination is

• The momentum remains constant. 
• Direction remains same.
• Kinetic energy and potential energy changes.
• Path of electron is constant
• Light is emitted.
• Suitable for fabrication of opto-electronic devices such as LED's

Indirect band gap semiconductor:

          These are normal semiconductors such as silicon and germanium. These do not have their conduction band minima directly above the valence band maxima. So that whenever the recombination takes place then the momentum is changed,in the diagram the valence band and conduction band are shown with multiple lines which are various energy levels as these are bands of energy. The energy band structure is shown below:

       In the figure the electrons from conduction band recombine with the holes in the valence band no directly but through the trapping levels,during the process of recombination and during the process energy is released in the form heat. The solid red line indicates the recombination process.Thus the name indirect band gap recombination and similarly the semiconducor. The properties of the indirect band gap recombination is

• The momentum changes.
• Direction remains same.
• Kinetic energy and potential energy changes.
• Path of electron changes
• Heat is liberated
• Not suitable for fabrication of opto-electronic devices such as LED's.

The above gives brief understanding regarding the direct and indirect band gap semiconductors.

Note: The half sine wave indicates that particles move in the form of waves.