Surface-emitting UV LEDs with small apertures
Fig. 1: Top emitter LED chip (400 µm x 400 µm) with ITO emission window
Fig. 2: Light power-current-voltage characteristics of a top emitter LED emitting through a circular aperture with a diameter of 90 µm (see insert).
For applications in medical technology, gas sensing, and security focusable and efficient light sources in the UVA spectral region (320 - 380 nm) are needed. UV LEDs are highly desirable since they can be easily integrated into systems and LED arrays. They are additionally suitable for battery-powered operation. In addition, shaping the radiation pattern using LED chips is fairly straightforward, if the LED acts as a point light source emitting from a small area. Moreover, if a hybrid lense is mounted onto such a chip, the collimation of the radiation could already be realized on chip level. Within the innovative regional growth core "Berlin WideBaSe", FBH with TU Berlin and the companies Jenoptik Polymer Systems and Sentech jointly develops focusable LEDs with an emission near 360 nm for applications in the analysis of bodily fluids.
In a first step, top-emitting LEDs have been fabricated which emit through a small area on the chip front side (Fig. 1). The emission is realized by using an optically transparent indium tin oxide (ITO) contact. The area through which the current flows is defined by using either insulating layers or ion implantation. Fig. 2 shows light-current-voltage characteristics of a 360 nm top-emitter LED with a homogeneous emission over a circular aperture of 90 µm in diameter. The optical power is 0.3 W at a diode current of 10 mA. In a next step it is intended to further increase the optical power by optimizing the extraction efficiency. Moreover, procedures to mount lenses on the chip will be developed in order to limit the angle of radiation to 90°.
FBH research: 01.11.2011