ABSTRACT
Figure 4.1 Structure of a typical epitaxial GaN blue LED wafer material showing the positions and thicknesses of various layers. This chapter presents results from an integrated programme of development and optimisation of patterning and dry-etch nanofabrication technologies for GaN-based LEDs. We show results on the processing of as-grown GaN LED wafers on sapphire, corresponding to process flows for conventional p-up LEDs. The processing techniques developed are applicable to thin GaN devices made by LLO routes, as well as to LEDs fabricated from non-nitride materials. The results to date have been obtained using 2 inch sapphire based wafers. However, the techniques developed are applicable to GaN device structures on larger sapphire wafers [20] and lower cost large silicon substrates [21]. Both these approaches are being actively pursued to reduce the epitaxy-related cost component of GaN LEDs. Our specific motivation concerned the development of PhQC LEDs for direct flat panel backlighting for LCDs. Results on the performance characteristics of devices made by optimised fabrication routes have been reported elsewhere [22].
