This thesis details research centering around GaN based light emitting diodes (LEDs) emitting at non-standard wavelengths i.e. outside of the blue region of the electromagnetic spectrum. The first part of the work focuses on developing a simple procedure which allows for the characterisation for loss mechanisms in high indium content LEDs. A strong quantum confined stark effect was observed and had a strong correlation with Poole-Frenkle emission, high forward and reverse bias leakage currents, reverse bias emission and suppressed light emission. These effects are largely attributed to epitaxy. The use of thin metal interlayer was studied as a means of improving current spreading layers. It was found that the inclusion of a thin Ni layer improved the contact resistance, leakage and wall plug efficiency of devices with both ITO and AZO contacts. Further to this it was found that annealing in O_2 and slightly increasing the thickness of the metal layer improved device characteristics. Finally a series of experiments showed that a structure free of a p-type layer could be used as a source of UV emission. These devices exhibited resonant tunnelling behaviour which correlated to enhanced light output.
