SSC CGL PREP GUIDE

Hi all,

SSC Combined graduate level consists of two exams tier1 and tier 2. Once if you get qualified for tier1 then only you will be allowed for tier2. Tier1 exam is not so hard to crack you need to have good practice so that you can reduce time taken to solve the problems as there will not be much complexity in the paper. For tier1 especially during the exam do not waste your time on the topics you are not confident on, as there is no sectional cutoff try to score maximum as part of your strength. General awareness section may not be so easy to crack keep faith in arithematic and reasoning.

For tier2 you need to more work especially on english. Try scoring the maximum so that you can reach your respective cutoff scores. This is not easy compared to tier1 the syllabus for mathematics is also heavy.

After you qualify for both the exams you will have the interview.

Syllabus for SSC CGL is as below questions may be asked out of these also:
TIER 1 Syllabus
TIER 2 Syllabus

For practice you have  a wide range of books available in the market.

All the best.
Thanks All :-) :-)

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.