III-nitride deep ultraviolet micro- and nano-photonics

Recent progresses in epitaxial growth, fundamental studies of high Al content AlGaN alloys with Si and Mg doping, light polarization properties, and deep UV LEDs combined with microlens or photonic crystal structure to improve light extraction are presented. For Si doped Al_0.7Ga_0.3N, a room temperature n-type resistivity as low as 0.0075 Ω·cm has been obtained. We have also achieved n-AlN with a free electron concentration and mobility of about 1.0 × 10¹⁷cm^-3 and 2 cm ²/Vs, respectively. For Mg doped Al_0.7Ga_0.3N, we have obtained a resistivity around 10⁵ Ω cm at room temperature and confirmed p-type conduction at elevated temperatures (> 700 K) with a resistivity of about 40 Ω cm at 800 K. Based on the optimized material growth, 280 nm deep UV LED with forward voltage of 6.7 V, and output power of 0.35 mW has been achieved at 20 mA. To enhance light extraction efficiency, sapphire microlens array was monolithically integrated on flip-chip bonded deep UV LED substrates; a light extraction enhancement of 55% was achieved. To improve the transverse light extraction, photonic crystal structures were incorporated into the devices, and significant light extraction enhancement was achieved.