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Research CART LED structures A novel GaN LED design based on a Two Well system with Charge Asymmetric ResonanceTunneling (CART). The system consists of two coupled wells: a Wide Well (WW) and active Quantum Well (QW). The wells are coupled via resonance tunneling barrier (RTB) transparent for electrons and blocking for holes . Resonance tunneling between two wells means that energy position of the WW bottom have to be equal to the energy position of the subband minimum of the active QW. This problem is solved by the adjusting alloy composition in WW and QW, and choosing proper QW width ~ 25 Å. Carrier Asymmetry of GaN. This design is based on the mass asymmetry of the electrons and holes in GaN. It allows to fit the electron subband position in active QW to the bottom of the WW and at the same time keep the hole subband minimum in QW lower than the bottom of the WW for holes and thus forbid the hole penetration without thermal activation in the WW. It is important that even the small amount of thermally activated holes have no possibility to tunnel into the WW for the chosen barrier width ( ~10Å) because of their heavy mass (mh=2m0). Advantages This design allows: - to increase capture efficiency of the electrons into the active QW due to direct tunneling of the electrons from WW into the QW - to suppress the electron leakage into the p-type layer - to eliminate parasitic UV light - to use WW as a good current spreading layer - to improve quality of the active QW because of mismatch reduction (~ 4 times). The reason is that the active In0.2 Ga0.8 N QW growth on highly tensile strained thin GaN barrier with the lattice parameter close to the one of the In0.15 Ga0.85 N WW - the WW also works as a stopping layer for the threading dislocations, because of the high stress on the interface n-GaN/ In0.15 Ga0.85 N - there is no need to use p-AlGaN as an element of the technology - to reduce the growth time since we expect that the same quality of the active QW will be achieved for thinner n-GaN layer
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