A p-n photodiode is made of a material with a bandgap of 2.0 eV. The minimum frequency of the radiation that can be absorbed by the material is nearly:

1.  $10\times {10}^{14} \mathrm{Hz}$

2.  $5\times {10}^{14} \mathrm{Hz}$

3.  $1\times {10}^{14} \mathrm{Hz}$

4.  $20\times {10}^{14} \mathrm{Hz}$

In the energy band diagram of a material shown below, the open circles and filled circles denote holes and electrons respectively. The material is a/an: 

1. p-type semiconductor

2. insulator

3. metal

4. n-type semiconductor