Improved UV Nitride Light Emitting Diode With Engineered Spontaneous and Piezoelectric Charges

Most III-V nitride light emitting diodes have an n-type down structure with Ga polarity. In such a device, the active layer is grown on top of the n-cladding layer and the p-type cladding layer is grown on top of the active layer. We have analyzed the band structure of such a device and found a reduced effective conduction band barrier due to the positive spontaneous and piezoelectric polarization charge, resulting in large electron overshoot and necessitating the introduction of the commonly employed electron blocking layer. On the other hand, the polarization charge at the corresponding interface for a p-type down device with Ga polarity is negative, resulting in a significant enhancement of the electron barrier and the existence of a 2D hole gas near the interface. These are beneficial to the performance of single heterojunction LEDs. We have fabricated and tested such a device with a peak efficiency above 100A/sq cm and only approx. 10% droop up to 500A/sq cm, which was achieved without the implementation of an AlGaN electron-blocking layer or a second hetero-interface. See also ADM002187. Proceedings of the Army Science Conference (26th) Held in Orlando, Florida on 1-4 December 2008, The original document contains color images.