GaN from certain direction pressure or tension, the

  GaN (Gallium nitride) is very hard and stable chemical compound and it’s melting point is about 2000K. Generally, the atomic structure for GaN (gallium nitride) is closed-packed hexagonal structure and that results in relatively low symmetry of lattice and strong piezoelectricity and ferroelectricity. The piezoelectricity describes when the lattice suffers from certain direction pressure or tension, the vertical surface of the coming force will obtain equal quantity inverse charges at two sides. The Ferroelectricity describes the spontaneous polarization when the structure of lattice don’t have a center of symmetry that makes the gravity center of positive and negative charges don’t coincide together leading to the electric moment and is not equal to 0. The two factors lead to very strong piezoelectric polarization and spontaneous polarization, totally it generates 5(MV/cm) which’s called breakdown electric energy.   GaN (Gallium nitride) is regard as the third generation wide band gap semiconductor. The band gap is 3.4 eV and thermal conductivity is 1.3 W/cm*K. The band gap is presented on electronic band structure which’s between valence band and conduction band. Normally valence bond refers to the band of energy occupied by the valence electrons and usually it’s the highest occupied band. Conduction Band is empty or may be defined as the lowest unfilled energy band. The term ‘band gap’ refers to the energy difference between the top of the valence bond and the bottom of the conduction band. Electrons could gain enough energy to jump to the conduction band by absorbing either a phonon or photon.   This two factors lead to the GaN (Gallium nitride) has a high working temperature and breakdown voltage and a strong ability of radiation resistance. The bottom of conduction band of GaN is at ? position which makes a huge energy difference with other with other valley to resist the scattering between different valleys. As a result, GaN has a very high saturated drift velocity of electrons.   Comparing semiconductors with insulators, semiconductors have a relatively smaller band gap and though both of them behave as insulator at absolute zero, for semiconductors , it allow thermal excitation of electrons into its conduction band at the temperature below its melting point. Generally, wide-band gap semiconductors materials have band gaps in the range of 2-4 eV, whereas typical semiconductors have band gaps in the range of 1-1.5 eV. Higher energy of band gap makes it suitable for working in a high temperature. Wide band gap semiconductors are associated with a high voltage. This is due to a large electric filed to generate carries through impact mechanism.   However, GaN also has its shortcomings. Because of it structure of energy bond, the electron mobility is relatively low while the charge carriers have a high valuable mass.   In general, all of the properties are very suitable for making radiation resistance, high frequency, high power and high density intergraded electronics in microwave power devices field.