GaN and related materials for high power application

摘要

Unique properties of GaN and related semiconductors make them superior for high-power applications. The maximum density of the two-dimensional electron gas at the GaN/AlGaN heterointerface or in GaN/AlGaN quantum well structures can reach 5x10~(13) cm~(-3), which is more than an order of magnitude highe than for traditional GaAs/AlGaAs heterostructures. The mobility-sheet carrier concentration product for these two dimensional systems might also exceed that for GaAs/AlGaAs heterostructures and can be further enhanced by doping the conducting channels and by using "piezoelectric" doping, which takes advantage of high piezoelectric constants of GaN and related materials. We estimate the current densities over 20 A/mm can be reached in GaN-based High Electron Mobility Transistors (HEMTs). These high current values can be combined with very high breakdown voltages in high-power HEMTs. These breakdown voltages are expected to rach several thousand volts. Recent Monte Carlo simulations point to strong ballistic and overshoot effects in GaN and related materials, which should be even more pronounced than in GaAs-based compounds but at much higher electric fields. This should allow us to achieve faster switching, minimizing the power dissipation during switching events. Self-heating, which is unavoidable in power devices, raises operating temperatures of power devices well above the ambient temperature. For GaN-based devices, the use of SiC substrates having high thermal conductivity is essential for ensuring an effective heat dissipation. SUch an approach combines the best features of both GaN and SiC technologies; and gaN/SiC-based semiconductors and heterostructures should find numerous applications in power electronices.