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In this work, InGaN/GaN multi-quantum wells (MQWs) high brightness light emitting diode (LED) was grown by metalorganic chemical deposition (MOCVD). Photoluminescence (PL), X-ray diffraction (XRD), cathodoluminescence (CL), transmission electron microscope (TEM) were performed on the LED wafers to investigate the effects of growth temperature, well width and In composition in the InGaN quantum well on the emitting wavelength of LED. It was found that the wavelength of InGaN MQW-LED shifted from about 400–470 nm due to the difference in the In composition introducing into the InGaN well layer at different growth temperature. It was also demonstrated that the wavelength can be changed from 470 nm to 504 nm only by changed the thickness of the InGaN quantum well layer. Combined with the CL image and TEM observation, it was concluded that the change from MQW structure to multi-quantum dot structure would be the cause of the shift from 470 to 504 nm by changed the InGaN well width. [Copyright &y& Elsevier]

Abstract: The negative capacitance behavior in light-emitting diodes and laser diodes has been observed and characterized by using ac admittance–voltage method. Experimental results proved that the strong negative capacitance behavior is always accompanied by remarkable light emission. We confirmed that the negative capacitance is an effect of the junction instead of other behavior or measurement error. We presented a numerical calculation by solving one dimension continuity equation based on a simple diode model. The results show that the negative capacitance behavior in light-emitting diodes has great relation to injected carriers recombination in the active region of luminescence. [Copyright &y& Elsevier]

Abstract: The temperature dependent diffusion and epitaxial behavior of oxidized Au/Ni/p-GaN ohmic contact were studied with Rutherford backscattering spectroscopy/channeling (RBS/C) and synchrotron X-ray diffraction (XRD). It is found that the Au diffuses to the surface of p-GaN to form an epitaxial structure on p-GaN after annealing at 450°C. At the same time, the O diffuses to the metal–semiconductor interface and forms NiO. Both of them are suggested to be responsible for the sharp decrease in the specific contact resistance (ρ c) at 450°C. At 500°C, the epitaxial structure of Au develops further and the O also diffuses deeper into the interface. As a result, the ρ c reaches the lowest value at this temperature. However, when annealing temperature reaches 600°C, part or all of the interfacial NiO is detached from the p-GaN and diffuses out, which cause the ρ c to increase greatly. [Copyright &y& Elsevier]

Current–voltage (I–V) characteristics, contact resistance, and optical transmittance measurements are performed to investigate the effects of different annealing ambient conditions on properties of contacts of Ni/Au/p-GaN. With increasing annealing temperature in the range from room temperature to 600 °C in air, I–V characteristics become linear, and the specific contact resistance (ρc) reduces continually. ρc of Ni (20 nm)/Au (50 nm) contact to p-GaN annealed in air at 600 °C is obtained as 2.76×10−2 Ω cm2. However, in N2 ambient, ρc is higher and shows a more complex evolution with increasing annealing temperature. The optical transmittance of the specimens increases and maintains a high value with the annealing temperature in air while it increases first, and then decreases monotonically in N2 atmosphere. We suggest that formation of low-resistance and high optical transmittance p-type Ohmic contact may be attributed to the oxidized Ni layer. The mechanism of Ohmic contact formation under different ambient conditions is also discussed. [Copyright &y& Elsevier]

Plasma-induced damage of n-type GaN in Cl2/CH4/Ar reactants and its recovery by the O2/CHF3 plasma in a reactive ion etching (RIE) system were studied by photoluminescence and Hall measurements. The mobility and optical properties of n-type GaN etched in Cl2/CH4/Ar were degraded gradually with increased radio frequency power. The effects of O2/CHF3 plasma treatment on the electrical and optical properties of n-type etched GaN were investigated by changing the ratio of O2/CHF3 flow rate. It was found that the damage caused by the conventional RIE process could be partly recovered by O2/CHF3 plasma treatment. The recovery mechanism was also discussed. [Copyright &y& Elsevier]

The evolution of wing tilt in laterally and epitaxially overgrown (LEO) GaN thick film was studied using cross-sectional transmission electron microscope (TEM) observation and high-resolution X-ray diffraction (XRD). The LEO GaN film was grown by hydride vapor epitaxy (HVPE) on Si(1 1 1) substrate. Horizontally propagating dislocations (HDs) and low density of threading dislocation (TD) in LEO wings were observed in TEM micrographs. Tilt of LEO wing to the GaN seed region was measured as 3.3° at interface of HVPE–GaN/metal organic vapor phase epitaxy (MOVPE)–GaN by selective area electron diffraction, which is much more than that in the surface region estimated as 0.4° by XRD measurements. With φ-scan XRD technique, we found that there exist many differences of tilts and twists of c-axis between the opposite wings on each mask. Asymmetry growth of the opposite wings on SiO2 mask may be due to the flow asymmetry of precursor in vertical reactor. The tilting generation and diminishing increasing with film thickness was discussed too. [Copyright &y& Elsevier]