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Applet Worksheet

1. Determine Eg for the different compositions of the AlGaAs alloy.  Indicate if it is a direct band gap or an indirect band gap.

  Composition   Eg   Direct or Indirect
 Al0.1Ga0.9As   _____    _____________
 Al0.4Ga0.6As   _____   _____________
 Al0.5Ga0.5As   _____   _____________
 Al0.9Ga0.1As   _____   _____________

2. What physical significance or consequence does the direct or indirect bandgap have (i.e., in terms of the light emission efficiency) ?  Explain !

3. Would the Light Emitting Diodes and Laser Diodes be made from a direct bandgap materials or from the indrect bandgap materials ?
              (a) direct bandgap materials                 (b) indirect bandgap materials

4. Why is the indirect bandgap materials so inefficient compared with the direct gap materials ?  Explain !