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The electrical performances of III-nitride blue micro-light-emitting diodes (µLEDs) with different tunnel junction (TJ) epitaxial architectures grown by metalorganic chemical vapor deposition are investigated. A new TJ structure that employs AlGaN is introduced. The current density–voltage characteristic is improved by incorporating AlGaN layer above the n-side of the TJ layer, and the effects of the AlGaN/GaN superlattices is examined. Based upon the data from band diagram simulation, net positive polarization charge is formed at the AlGaN/GaN interface, which results in a reduction in tunneling distance and increase in tunneling probability. Moreover, similar electrical improvement is observed in various device dimensions and is independent of operating current density, suggesting that AlGaN/GaN biaxial tensile strain or current spreading is not the main contribution for the improvement. Finally, the effects on the efficiency performances are determined. While the maximum external quantum efficiency of the TJ devices remains identical, the wall-plug efficiency of µLEDs is enhanced significantly by the proposed AlGaN-enhanced TJ design. This work reveals the possibility of energy efficient TJ contact with high transparency in the visible wavelength range. [ABSTRACT FROM AUTHOR]

The impact of AlGaN growth conditions on AlGaN:Si resistivity and surface morphology has been investigated using metalorganic chemical vapor deposition. Growth parameters including growth temperature, growth rate, and trimethylindium (TMI) flow have been systematically studied to minimize the resistivity of AlGaN:Si. We observed a strong anticorrelation between AlGaN:Si conductivity and growth temperature, suggesting increased silicon donor compensation at elevated temperatures. Secondary ion mass spectrometry and positron annihilation spectroscopy ruled out compensation by common impurities or group-III monovacancies as a reason for the observed phenomenon, in contrast to theoretical predictions. The underlying reason for AlGaN:Si resistivity dependence on growth temperature is discussed based on the possibility of silicon acting as a DX center in Al0.65Ga0.35N at high growth temperatures. We also show remarkable enhancement of AlGaN:Si conductivity by introducing TMI flow during growth. A minimum resistivity of 7.5 mΩ cm was obtained for n-type Al0.65Ga0.35N, which is among the lowest reported resistivity for this composition. [ABSTRACT FROM AUTHOR]

The role of water (H2O) vapor in reducing background impurity concentration in epitaxial Ga2O3 thin films grown by metalorganic chemical vapor deposition (MOCVD) was studied. Adding H2O vapor to oxygen was found to increase the surface roughness and decrease the carrier concentration but have no effect on the structural quality and RT electron mobility of both the UID and doped films. The H2O vapor promotes the growth of the stable (110) and 1 ¯ 10 facets elongated along the [001] direction. Using [H2O] of 250 ppm, the β-Ga2O3 films showed a RMS roughness of >13 nm, which is much higher than that measured for similar films grown without H2O (RMS = 0.8 nm). The electron mobility of the UID Ga2O3 layers grown with and without water vapor was ∼150 cm2/V s, while the carrier concentration dropped by ∼2.5× after increasing the [H2O] to 6000 ppm. Similarly, for the lightly Si doped films, the RT carrier concentration dropped from 5.4 × 1015 cm−3 ([H2O] = 0 ppm) to 3.4 × 1015 cm−3 ([H2O] = 250 ppm), leaving the mobility unaffected. The results offer a new method of using water vapor assisted growth of Ga2O3 films with low RT carrier concentration that are required for the realization of high-performance electronic power devices with high breakdown voltages. [ABSTRACT FROM AUTHOR]