1 Power GaN Device Material
Si GaAs AlN GaN Material Properties
Additional Document 1
Additional Document 2
3 Vertical GaN and SiC Power Device
Explanation on Energy Bands
In semiconductors, the outermost valence electrons completely fill the allowable energy band (that is, the valence band), There is an energy gap to the next higher energy band (Fig. 2.11). At temperatures above 0K, the valence band is not completely filled because a few electrons have enough thermal energy to be excited across the energy gap into the next allowed energy band. Since electrons in the upper energy band can generate a current in response to an applied electric field, the upper energy band is called the conduction band. The bottom edge of the conduction band and the top edge of the valence band are usually denoted by EC and EV, respectively.
In semiconductors, EC and EV are functions of crystal momentum, and the energy gap Eg is defined as the difference between the minimum EC and maximum EV (Figure 2.12). For direct bandgap semiconductors (such as AlN and GaN), the momentum at which EC reaches a minimum is the same as that at which EV reaches a maximum (Fig. 2.12[a]); however, for indirect bandgap semiconductors (such as silicon and silicon carbide) , they are different (Fig. 2.12[b]).