Alexander Wilm

Determination of recombination coefficients in InGaN quantum-well light-emitting diodes by small-signal time-resolved photoluminescence

We suggest a novel technique for the evaluation of the recombination coefficients corresponding to Shockley–Read–Hall, radiative, and Auger recombination that occur in InGaN/GaN-based light-emitting diodes (LEDs). This technique combines the measurement of the LED efficiency as a function of LED drive current with a small-signal time-resolved photoluminescence measurement of the differential carrier life time (DLT). Using the relationships between the efficiency and DLT following from the empirical ABC-model, one can evaluate all three recombination coefficients. The suggested technique is applied to a number of single- and multiple-quantum well LEDs to gain a deeper insight into the mechanisms ultimately limiting their efficiency.

Requirements on LEDs in etendue limited light engines

Light engines used in projection systems often set constraints on the design and system application of the LED light source. In these advanced optical systems the optical extend of the LED light source is limited due the etendue of the imager. The etendue is defined as the product of emitting area and viewing angle. This paper shows how the LED light source is constrained by the laws of optics and how these limits influence the light source design. To achieve an efficient system design, the variables that must be optimized include the primary optics, LED package design and chip technology. The LED light sources which are best suited for these applications and requirements will also be demonstrated and discussed.

Requirements on LEDs for advanced optical systems

The use of LEDs in advanced optical systems such as LED projectors or automotive headlamps is usually limited by the optical extend of the light source. The optical extend (or étendue) is defined as the product of the optical area and the divergence angle of the emission. In our paper, we discuss the consequences of such limitations on the design and performance of optical systems. The system optimization involves the chip technology, package design and the primary optics, producing an optical extend that has to match with the optical extend of the imager component. It will be shown how these optical laws put constraints on the LED light source and the design of suitable light engines. The benefits of LED light sources for the above mentioned applications will also be demonstrated.