Mask-less ultraviolet photolithography based on CMOS-driven micro-pixel light emitting diodes.

We report on an approach to ultraviolet (UV) photolithography and direct writing where both the exposure pattern and dose are determined by a complementary metal oxide semiconductor (CMOS) controlled micro-pixellated light emitting diode array. The 370 nm UV light from a demonstrator 8 x 8 gallium nitride micro-pixel LED is projected onto photoresist covered substrates using two back-to-back microscope objectives, allowing controlled demagnification. In the present setup, the system is capable of delivering up to 8.8 W/cm2 per imaged pixel in circular spots of diameter approximately 8 microm. We show example structures written in positive as well as in negative photoresist.

Individually-addressable flip-chip AlInGaN micropixelated light emitting diode arrays with high continuous and nanosecond output power.

Micropixelated blue (470 nm) and ultraviolet (370 nm) AlInGaN light emitting diode ('micro-LED') arrays have been fabricated in flip-chip format with different pixel diameters (72 microm and 30 microm at, respectively, 100 and 278 pixels/mm(2)). Each micro-LED pixel can be individually-addressed and the devices possess a specially designed n-common contact incorporated to ensure uniform current injection and consequently uniform light emission across the array. The flip-chip micro-LEDs show, per pixel, high continuous output intensity of up to 0.55 microW/microm(2) (55 W/cm(2)) at an injection current density of 10 kA/cm(2) and can sustain continuous injection current densities of up to 12 kA/cm(2) before breakdown. We also demonstrate that nanosecond pulsed output operation of these devices with per pixel onaxis average peak intensity up to 2.9 microW/microm(2) (corresponding to energy of 45pJ per 22ns optical pulse) can be achieved. We investigate the pertinent performance characteristics of these arrays for micro-projection applications, including the prospect of integrated optical pumping of organic semiconductor lasers.

Integration by self-aligned writing of nanocrystal/epoxy composites on InGaN micro-pixelated light-emitting diodes.

We report on the integration of monodisperse semiconductor nanocrystal (NC) color converters onto gallium nitride ultraviolet micro-pixelated light-emitting diodes ('micro-LEDs'). Integration is achieved in a 'self-aligned' process by forming a nanocomposite of the respective NCs in a photocurable epoxy polymer. Blue, green, yellow and red NC/epoxy blend microstructures have been successfully integrated onto micro-pixelated LEDs by this technique and utilised for color conversion, resulting in a five color emission single chip. Optical output power density of up to about 166 mW/cm2 is measured; spectral emission at 609 nm gives an estimated optical-to-optical conversion as high as 18.2% at 30 mA driving current.

All-optical extinction-ratio enhancement of a 160 GHz pulse train by a saturable-absorber vertical microcavity.

A vertical-access passive all-optical gate has been used to improve the extinction ratio of a 160 GHz pico-second pulse train at 1555 nm. An extinction ratio enhancement of 6 dB is observed within an 8 nm bandwidth. Such a device is a promising candidate for low-cost all optical reamplication and reshaping (2R) regeneration at 160 Gbits/s.