Barrier Inhomogeneity of Schottky Diode on Nonpolar AlN Grown by Physical Vapor Transport

An aluminum nitride (AlN) Schottky barrier diode (SBD) was fabricated on a nonpolar AlN crystal grown on tungsten substrate by physical vapor transport. The Ni/Au-AlN SBD features a low ideality factor n of 3.3 and an effective Schottky barrier height (SBH) of 1.05 eV at room temperature. The ideality factor n decreases and the effective SBH increases at high temperatures. The temperature dependences of n and SBH were explained using an inhomogeneous model. A mean SBH of 2.105 eV was obtained for the Ni-AlN Schottky junction from the inhomogeneity analysis of the current-voltage characteristics. An equation in which the parameters have explicit physical meanings in thermionic emission theory is proposed to describe the current-voltage characteristics of inhomogeneous SBDs.Comment: 6 pages, 6 figure

First Principles Study on Li-doped and Li,O-codoped AlN

This paper focuses on the detailed investigation of the structural and electronic properties of wurtzite AlN crystals doped by Li with and without oxygen with the first principles calculation. All the calculations have exhibited significant structural distortions. Compared with the monoclinic doping, the oxygen codoping has improved the structure deformation and lowered the formation energy of Li dopants. The calculated electronic density of states (DOS) reveals that all doping configurations still preserve semiconductor characteristics. The states around the valence band maximum cross the Fermi level, which implies p-type doping. The induced extra levels are extremely localized and flat in Li-doped AlN while much more delocalized in oxygen codoped models. The mono-doping of Li is in general energetically unfavorable while the codoping improves the formation and makes the intercalation of Li more stable in AlN. According to the results, the codoping configuration of Li with O in AlN has provided a useful way of modifying the corresponding properties

Simulation and Experiment for Growth of High-Quality and Large-Size AlN Seed Crystals by Spontaneous Nucleation

Seed crystals are the prerequisite for the growth of high quality and large size aluminum nitride (AlN) single crystal boules. The physical vapor transport (PVT) method is adopted to grow AlN seed crystal. However, this method is not available in nature. Herein, the temperature field distribution in the PVT furnace was simulated using the numerical analysis method to obtain free-standing and large-size seeds. The theoretical studies indicate that the temperature distribution in the crucible is related to the crucible height. According to the theory of growth dynamics and growth surface dynamics, the optimal thermal distribution was achieved through the design of a specific crucible structure, which is determined by the ratio of top-heater power to main-heater power. Moreover, in our experiment, a sole AlN single crystal seed with a length of 12 mm was obtained on the tungsten (W) substrate. The low axial temperature gradient between material source and substrate can decrease the nucleation rate and growth rate, and the high radial temperature gradient of the substrate can promote the expansion of crystal size. Additionally, the crystallinity of the crystals grown under different thermal field conditions are analyzed and compared. The Raman results manifest the superiority of the thermal inversion method in the growth of high quality AlN single crystal

Broadband White-Light Emission from Alumina Nitride Bulk Single Crystals

Alumina nitride bulk single crystals (AlN BSCs) were grown using a two-heater Physical Vapor Transport (th-PVT) method. The crystal contains massive lattice defects including aluminum vacancy (V_Al) and oxygen substitution (O_N). The photoluminescence (PL) spectrum of the crystal demonstrated a broad emission covering from 250 to 1000 nm. By study the PL spectrum, abundant midgap states in the wide band gap of AlN were nailed down. Based on the crystals, metal-AlN-metal Schottky devices were fabricated. These devices emitted high quality white light with color rendering index (CRI) over 90 under a bias of 60 V. Moreover, it was found that the white light emitting property of AlN BSCs was adjustable through changing impurity density and device structure. This research aims to pave a new way for solid-state white light source