Researchers at the University of California, Santa Barbara (UCSB) recently reported the first package of high-power, high-efficiency semi-polar (30-3-1) blue LEDs (452nm). For related articles, please see Ingrid L. Koslow et al. In the Japanese Journal of Applied Physics Journal Vol 49, p080203 article. UCSB has been studying the growth of LEDs and lasers in a number of different semi-polar crystals since last year, hoping to achieve better performance than devices grown on conventional polar c-planes.
The external quantum efficiency (EQE) of the c-plane device can reach up to 60%, which seems difficult to be surpassed. This is also an advantage of mature technology, and the growth of other crystal-oriented materials is still at a relatively early stage, meaning that these materials generally have a higher defect density (about 10 10 /cm 2 ) than materials grown on the c-plane. However, c-plane devices that want such high EQE values ​​require quite special operating conditions, such as special current and temperature control. What we really need is to be able to work under a variety of conditions and achieve high efficiency and high power.
Semi-polar and polar materials are believed to grow better devices because of the lower electric field strength in the active region. In polar devices, the electric field can cause the Quantum-confined Starker Effect (QCSE) to separate electrons and holes, so the radiation recombination takes longer than other mechanism processes, eventually illuminating Reduced efficiency. The above electric field is derived from the spontaneous polarization and piezoelectric polarization of the nitride semiconductor material (related to stress conditions within the material).
UCSB researchers say that the (30-3-1) crystal plane they used in recent experiments differs from the (20-21) crystal plane by only 5°, which is in the green laser recently developed by Sumitomo Electric in Japan. The performance is expected.
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