The characteristics of the nitride-based blue light-emitting diode (LED) with an AlGaN/GaN superlattice (SL) electron-blocking layer (EBL) of gradual Al mole fraction are analyzed numerically and experimentally. The emission spectra, carrier concentrations in the quantum wells, energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results indicate that the LED with an AlGaN/GaN SL EBL of gradual Al mole fraction has a better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in its active region over the LED with a conventional rectangular AlGaN EBL or with a normal AlGaN/GaN SL EBL. The results also show that the efficiency droop is markedly improved when the SL EBL of gradual Al mole fraction is used.

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Wang et al: Performance analysis of GaN-based light-emitting diodes with lattice-matched InGaN/AlInN/InGaN quantum well barriers 1 Abstract-The properties of GaN-based light-emitting diodes (LEDs) with lattice-matched InGaN/AlInN/InGaN (LM-IAI) quantum well (QW) barriers are investigated numerically. Distributions of electrostatic field, carrier current density, carrier concentration and radiative recombination rate are simulated, and internal quantum efficiency (IQE) and emission power are calculated. The results show that the LEDs with LM-IAI barriers have higher IQE and emission power over their conventional counterparts with GaN barriers due to the mitigation of the quantum-confined Stark effect and the suppression of electron leakage. Furthermore, the performances of the nitride-based LEDs with the proposed barriers can be further improved by dismissing the electron-blocking layer, which is attributed to the improvement of hole injection efficiency and the decrease of overall Auger recombination. Index Terms-AlInN, light-emitting diodes (LEDs), multilayer barrier, quantum efficiency. 1551-319X (c)

A common AlGaN/GaN current-aperture vertical effect transistor (CAVET) with a SiO 2 current blocking layer on the GaN substrate is compared to two similar structures with the stepped and linearly graded AlGaN barrier layer, respectively. The approach resulted in high threshold voltages (V th ) of −2.6 V and −3.6 V, compared to V th = −4.4 V for the common device. And the breakdown voltage of two modified CAVETs was increased from 541 V to 711 V and 613 V, respectively. This reveals the great potential of polarization doping for fabricating enhancement-mode and high-voltage power transistors. A mechanism accounting for the improvement in the device performance by modulating the heterojunction electron gas (HEG) is presented. Meanwhile the stepped graded AlGaN is discovered to be better than the linearly graded AlGaN in modulating the HEG. Furthermore, a trench structure is involved in the AlGaN/GaN CAVET with the stepped graded AlGaN in order to obtain an enhancement-mode device. A positive threshold voltage of 0.6 V and a breakdown voltage exceeding 800 V are demonstrated.