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What are the advantages and disadvantages of gallium nitride?

wallpapers Industry 2021-04-08
Disadvantages and problems of gallium nitride
On the one hand, theoretically due to the band structure of gallium nitride, the effective mass of carriers is larger and the transport properties are poor, so the low electric field mobility is low and the high-frequency performance is poor.
On the other hand, the GaN single crystal grown by heteroepitaxial technology is not satisfactory. For example, the dislocation density has reached 108~1010/cm2 (although the crystal structure of sapphire and SiC is similar to that of GaN, there are still Relatively large lattice mismatch and thermal mismatch); the room temperature background carrier concentration of undoped GaN is as high as 1017cm-3, and it exhibits n-type conductivity; although it is easy to achieve n-type doping, the p-type doping level Too low, the resulting hole concentration is only 1017~1018/cm3, the mobility is <10cm2/Vs, and the doping efficiency is only 0.1%~1%.
 
Advantages of gallium nitride
① With large forbidden bandwidth (3.4eV) and high thermal conductivity (1.3W/cm-K), the working temperature is high, the breakdown voltage is high, and the radiation resistance is strong;
② The bottom of the conduction band is at the Γ point, and the energy difference between it and the other energy valleys of the conduction band is large, it is not easy to produce inter-valley scattering so that a high strong field drift velocity can be obtained;
③GaN is easy to form mixed crystals with AlN, InN, etc., and can be made into various heterostructures. The 2-DEG with mobility of 105cm2/Vs at low temperature has been obtained;
④Lattice symmetry is relatively low (hexagonal wurtzite structure or tetragonal metastable sphalerite structure), with strong piezoelectricity and ferroelectricity : Strong piezoelectric polarization and spontaneous polarization are generated near the heterojunction interface, which induces a very high density of interface charges, strong The energy band structure of the heterojunction is modulated, and the two-dimensional space limitation of 2-DEG is strengthened, thereby increasing the areal density of 2-DEG, which is meaningful for device operation.
 
In short, from the overall point of view, the advantages of gallium nitride make up for its shortcomings, especially through the role of heterojunction, its effective transport performance is no less than GaAs, and the effect of making microwave power devices is still not inferior to GaAs. It is often far superior to all existing semiconductor materials.

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