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High carrier injection efficiency at high carrier densities for UV light emitting devices


Despite the significant progress in nitride emitters for both the visible and the UV spectral range, no electrically driven laser diode with emission wavelength shorter than 336nm could be demonstrated so far. Besides the difficulties in the growth of high aluminum containing layers and the realization of highly conductive p-type material, carrier injection has been identified as a major issue for UV emitters. Limited carrier injection has already been discussed as a mechanism contributing to the so-called “droop” in visible light emitting diodes at high drive currents. The situation becomes even more problematic for shorter wavelength emitters due to reduced hole concentrations and mobilities for the higher band gap materials. Using a conventional EBL design both good hole injection and good electron blocking can typically not be achieved for high drive current densities.

We modeled and experimentally verified that for a UV laser diode heterostructure with a target wavelength of 290nm the use of a conventional EBL design (e.g., 8nm, Al69Ga31N) results in a significant loss of electrons leaking out over the EBL. To overcome this dilemma, we designed and experimentally implemented a novel EBL concept that can provide both high hole injection capability and electron blocking at the same time. The idea is based on a polarization assisted, composition-graded p-AlGaInN EBL that increases the effective hole concentration within the EBL and lowers the energy barriers at the interfaces for efficient hole injection. With this approach we could show in both the model and the experiment that the device efficiency can be significantly improved for the high drive currents that are needed for laser operation or high power LEDs.

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Wunderer, T.; Northrup, J. E.; Yang, Z.; Teepe, M. R.; Chua, C. L.; Johnson, N. M. High carrier injection efficiency at high carrier densities for UV light emitting devices. Tenth International Conference on Nitride Semiconductors; 2013 August 25-30; Washington, DC.