Optical Performance of N-Face A1GaN Ultraviolet Light Emitting Diodes

The optical property and injection efficiency of N-face A1GaN based ultraviolet light emitting diodes （UV-LEDs） are studied and compared with Ga-face A1GaN based UV-LEDs. A staircase electron injector is introduced in the N-face AIGaN based UV-LED. The electroluminescence spectra, power-current performance curves, energy band diagrams, carrier concentration and radiative recombination rate are numerically calculated. The results indicate that the N-face UV-LED has a better optical performance than the Ga-face UV-LED, and the injection efficiency is enhanced owing to the fact that the staircase electron injector is available for UV-LEDs.     

Polarization Induced High A1 Composition A1GaN p-n Junction Grown on Silicon Substrates

Wide bandgap Alx Ga1-x N （x = 0.7-1） p-n junction is realized on a silicon substrate through polarization induced doping. Polarization induced positive charge field is produced by linearly grading from A1N to Al0.7Ga0.3N, and negative charge field is generated by an inverted grading from A10.7Ga0.3N to A1N. The polarization charge field induced hole density is on the order of 10^18 cm^-3 in the graded AIxGaI-xN：Be （x = 0.7-1） p-n junction. Polarization doping provides a feasible way to mass produce lll-nitride devices on silicon substrates.     

Low-resistance Ohmic contact on polarization-doped AIGaN/GaN heterojunction

High electronic density is achieved by polarization doping without an impurity dopant in graded AIGaN films. Low specific contact resistance is studied on the polarization-doped A1GaN/GaN heterojunctions by using the transmission line method （TLM）. The sheet density of polarization-doped A1GaN/GaN heterojunction is 6 × 10 14 cm-2 at room temperature. The linearly graded material structure is demonstrated by X-ray diffraction. The cartier concentration and mobility are characterized by a temperature-dependent Hall measurement. Multiple-layer metal （Ti/A1/Ti/Au） is deposited and annealed at 650 ℃ to realize the Ohmic contacts on the graded A1GaN/GaN heterojunctions.     

Low-resistance Ohmic contact on polarization-doped AlGaN/GaN heterojunction

High electronic density is achieved by polarization doping without an impurity dopant in graded AlGaN films. Low specific contact resistance is studied on the polarization-doped AlGaN/GaN heterojunctions by using the transmission line method(TLM). The sheet density of polarization-doped AlGaN/GaN heterojunction is 6×1014cm-2at room temperature.The linearly graded material structure is demonstrated by X-ray diffraction. The carrier concentration and mobility are characterized by a temperature-dependent Hall measurement. Multiple-layer metal(Ti/Al/Ti/Au) is deposited and annealed at 650°C to realize the Ohmic contacts on the graded AlGaN/GaN heterojunctions.