Quaternary InAlGaN based deep UV LED with high-Al-content p-type AlGaN

For the realization of 250-350 nm band deep ultraviolet (UV) emitters using group III-nitride materials, it is required to obtain high-efficiency UV emission and hole conductivity for wide-bandgap (In)AlGaN. For achieving high-efficiency deep UV emission, it is quite effective to use In segregation effect which has been already used for InGaN blue emitting devices. We have demonstrated high-efficiency UV emission by introducing several percent of In into AlGaN in the wavelength range of 300-360 nm at room temperature with an In segregation effect. The emission fluctuation in the submicron region due to In segregation was clearly observed for the quaternary InAlGaN epitaxial layers. An internal quantum efficiency as high as 15 % was estimated from quaternary InAlGaN based single quantum well (SQW) at around 350 rim at room temperature. Such a high efficiency UV emission can be obtained even on high threading dislocation density buffers. Also, hole conductivity was obtained for high Al content (>53%) Mg-doped AlGaN by using alternative gas flow growth process in metal-organic vapor phase epitaxy (MOVPE). Using these techniques we fabricated 310 rim band deep UV light-emitting diodes (LEDs) with quaternary In(x)AlyGa(1-x-y)N active region. We achieved output power of 0.4 mW for a 308 nm LED and 0.8 mW for a 314 rim LED under room temperature pulsed operation.