Alexander F. Pfeuffer

Micro-pixel light emitting diodes: Impact of the chip process on microscopic electro- and photoluminescence

We investigated the influence of a μ-pixelated chip process on the photoluminescence (PL) and electroluminescence (EL) of a monolithic InGaN/GaN based blue light emitting diode with a continuous n-GaN layer. Particularly, we observed the impact of the metallic p-contact on the PL emission wavelength. A PL wavelength shift in the order of 10 nm between contacted and isolated areas was assigned to screening of internal piezoelectric fields due to charge carrier accumulation. μPL and μEL mappings revealed correlated emission wavelength and intensity inhomogeneities, caused by the epitaxial growth process. The edges of single pixels were investigated in detail via resonant confocal bias-dependent μPL. No influence on the intensity was observed beyond 300 nm away from the edge, which indicated a good working edge passivation. Due to the low lateral p-GaN conductivity, the μPL intensity was enhanced at isolated areas.

A thermally enhanced bond interface for pixelated LEDs in adaptive front lighting systems

Pixelated LEDs are a new, high efficient light source which allows to control the beam pattern and which are therefore suitable for adaptive front light systems. We will present a concept for hybrid 3D flip chip stacking of pixelated LED chips onto an active matrix driver IC using a new interconnect structure to address thermal management and bonding robustness challenges. Two types of interconnect materials have been investigated: electroplated AuSn solder and nanoporous gold (NPG). We will present the deposition methods and the bonding approach for chip-to-chip and chip-to-wafer bonding and the characteristic results of the bonded interconnects achieved.