Growth and mechanisms for rare-earth-doped gallium nitride electroluminescent devices (ELDs)

Rare-earth (RE)-doped GaN has been shown to be an extremely versatile optoelectronic material, with light emission throughout the visible spectrum as well as at important near-infrared wavelengths. RE-doping of GaN has resulted in the successful fabrication of electroluminescent devices (ELD) with red, green and blue (RGB) color emissions using Eu, Er and Tm, respectively. Throughout studies with GaN:REs we have observed that RE optical emission from GaN films is a strong function of the parameters such as RE concentration, Ga flux, growth temperature and so on. Therefore, it was necessary to study the effect of those parameters on optical and structural properties of RE-doped GaN films by using Er-doped GaN in order to maximize ELD brightness and efficiency as well as to apply the results to real devices.; As a result of optimization, we reached a conclusion: (1) the optimum Er concentration is ∼1 at. % based on visible and IR PL, visible EL, visible PL lifetime and XRD; (2) Growth temperature of 600°C seems optimum in terms of PL and EL intensity as well as structural properties such as surface roughness and crystalline quality; (3) The optimum growth condition of Er optical activity is under slightly N-rich flux near the stoichiometric region.; Optically active GaN:RE films can be grown at surprisingly low temperatures (≤100°C) including room temperature. Combining this result with the optimized conditions, we have fabricated integrated EL devices emitting 2 colors, red and green, on GaN:Er and GaN:Eu films grown separately on the same substrate. We can say that 3-color integration is now possible and ready for real application with these techniques.