We report the realization and properties of a high-resolution solid-state self-emissive microdisplay based on III-nitride semiconductor micro-size light emitting diodes (µLEDs) capable of delivering video graphics images. The luminance level of III-nitride microdisplays is several orders of magnitude higher than those of liquid crystal and organic-LED displays. The pixel emission intensity was almost constant over an operational temperature range from 100 to −100 °C. The outstanding performance is a direct attribute of III-nitride semiconductors. An energy efficient active drive scheme is accomplished by hybrid integration between µLED arrays and Si CMOS (complementary metal–oxide–semiconductor) active matrix integrated circuits. These integrated devices could play important roles in emerging fields such as biophotonics and optogenetics, as well as ultra-portable products such as next generation pico-projectors.

We report on the fabrication and photovoltaic characteristics of InGaN solar cells by exploiting InGaN/GaN multiple quantum wells (MQWs) with In contents exceeding 0.3, attempting to alleviate to a certain degree the phase separation issue and demonstrate solar cell operation at wavelengths longer than previous attainments (>420 nm). The fabricated solar cells based on In0.3Ga0.7N/GaN MQWs exhibit an open circuit voltage of about 2 V, fill factor of about 60%, and an external efficiency of 40% (10%) at 420 nm (450 nm).

Hexagonal boron nitride (hBN) has emerged as an important material for various device applications and as a template for graphene electronics. Low-dimensional hBN is expected to possess rich physical properties, similar to graphene. The synthesis of wafer-scale semiconducting hBN epitaxial layers with high crystalline quality and electrical conductivity control has not been achieved but is highly desirable. Large area hBN epitaxial layers (up to 2 in. in diameter) were synthesized by metal organic chemical vapor deposition. P-type conductivity control was attained by in situ Mg doping. Compared to Mg-doped wurtzite AlN, which possesses a comparable energy band gap (∼6 eV), dramatic reductions in Mg acceptor energy level and P-type resistivity (by about six to seven orders of magnitude) have been realized in hBN epilayers. The ability of conductivity control and wafer-scale production of hBN opens up tremendous opportunities for emerging applications, ranging from revolutionizing p-layer approach in III-nitride deep ultraviolet optoelectronics to graphene electronics.

Deep ultraviolet ͑UV͒ photoluminescence ͑PL͒ spectroscopy has been employed to study deep impurity transitions in Al x Ga 1−x N ͑0 ഛ x ഛ 1͒ epilayers. Two groups of deep impurity transitions were observed, which are assigned to the recombination between shallow donors and two different deep level acceptors involving cation vacancies ͑V cation ͒ and V cation complexes in Al x Ga 1−x N alloys. These acceptor levels are pinned to two different energy levels common to Al x Ga 1−x N alloys ͑0 ഛ x ഛ 1͒. The deep impurity transitions related with V cation complexes were observed in Al x Ga 1−x N alloys between x = 0 and 1, while those related with V cation were only observed in Al x Ga 1−x N alloys between x = 0.58 and 1. This points out to the fact that the formation of V cation is more favorable in Al-rich AlGaN alloys, while V cation complexes can be formed in the whole range of x between 0 and 1. The implications of our findings to the UV optoelectronic devices using AlGaN alloys are also discussed.

We present the growth, fabrication, and photovoltaic characteristics of Inx Ga1−xN/GaN(x∼0.35) multiple quantum well solar cells for concentrator applications. The open circuit voltage, short circuit current density, and solar-energy-to-electricity conversion efficiency were found to increase under concentrated sunlight. The overall efficiency increases from 2.95% to 3.03% when solar concentration increases from 1 to 30 suns and could be enhanced by further improving the material quality.

Deep ultraviolet photoluminescence ͑PL͒ spectroscopy has been employed to investigate impurity transitions in Si doped Al-rich AlGaN alloys. In addition to the previously reported donor compensating centers-isolated cation vacancy with three negative charges ͑V III ͒ 3− and cation vacancy complex with two-negative charges ͑V III complex͒ 2− -a group of impurity transitions with higher emission energies has been observed in AlGaN alloys grown under different conditions, which has been assigned to the recombination between shallow donors and cation vacancy complexes with one-negative charge ͑V III complex͒ −1 . Similar to ͑V III ͒ 3− and ͑V III complex͒ 2− , the energy levels of ͑V III complex͒ 1− deep acceptors in Al x Ga 1−x N ͑0 ഛ x ഛ 1͒ alloys are pinned to a common energy level in vacuum. A strong correlation between the resistivity and PL emission intensities of the impurity transitions associated with cation vacancies ͑and complexes͒ was found.

High quality AlN epilayers were grown on sapphire substrates by metal organic vapor deposition and exploited as active deep ultraviolet ͑DUV͒ optoelectronic materials through the demonstration of AlN metal-semiconductor-metal ͑MSM͒ photodetectors. DUV photodetectors with peak responsivity at 200 nm with a very sharp cutoff wavelength at 207 nm have been attained. The AlN MSM photodetectors are shown to possess outstanding features that are direct attributes of the fundamental properties of AlN, including extremely low dark current, high breakdown voltage, and high DUV to visible rejection ratio and high responsivity. The results demonstrate the high promise of AlN as an active material for DUV device applications.

Deep ultraviolet photoluminescence spectroscopy was employed to study the impurity transitions in Mg-doped AlGaN alloys. A group of deep level impurity transitions was observed in Mg-doped AlxGa1−xN alloys, which was identified to have the same origin as the previously reported blue line at 2.8eV in Mg-doped GaN and was assigned to the recombination of electrons bound to the nitrogen vacancy with three positive charges (VN3+) and neutral Mg acceptors. Based on the measured activation energies of the Mg acceptors in AlGaN and the observed impurity emission peaks, the VN3+ energy levels in AlxGa1−xN have been deduced for the entire alloy range. It is demonstrated that the presence of high density of VN3+ deep donors translates to the reduced p-type conductivity in AlGaN alloys due to their ability for capturing free holes.