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We identify that the stimulated emission of GaN laser diodes (LDs) emerges far below the traditionally recognized threshold from both optical and electrical experiments. Below the threshold, the linear-polarized stimulated emission has been the dominating part of overall emission and closely related to resonant cavity. Its intensity increases super linearly with current while that of spontaneous emission increases almost linearly. Moreover, the separation of quasi-Fermi levels of electrons and holes across the active region has already exceeded the photon emission energy, namely, realized the population-inversion.

Temperature-dependent ac current-voltage-capacitance characteristics between 90 K and 440 K were investigated for InGaN/GaN multi-quantum-wells blue light-emitting diodes (LEDs) under high forward bias. Under large forward current, deep saturation of junction voltage Vj was observed over a wide temperature range. It was found that Vj corresponds to the separation energy of electron and hole quasi-Fermi levels and its temperature dependence could be well explained by the flat band model. After the pinning of quasi-Fermi levels, the forward current is dominated by the drift current in the p -GaN access layer. Considering Poole-Frenkel effect, a quantitative model was developed to reproduce the cur-rent-voltage characteristics of LEDs under high forward bias. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We report the stimulated emission related anomalous behavior of electrical parameters in GaN-based laser diodes based on both experiments and self-consistent calculations. In particular, the separation of quasi-Fermi levels of electrons and holes across active region shows a drop (or 'pinning') in threshold region, followed by an increase with current. The start and end points correspond to the two kink points of the first derivative of the optical output power-current (P-I) curve. This abnormal change of electrical parameters always satisfies the need of sufficient carriers for stimulated emission in the process of transition to lasing as well as lasing enhancement. [ABSTRACT FROM AUTHOR]

detailed study is presented on magnetic, electrical and optical properties of GaMnN: Si film grown by metal organic chemical vapor deposition (MOCVD) with high-purity SiH as the Si dopant source. The room-temperature field dependence magnetization and zero-field-cooled (ZFC)/field-cooled (FC) measurements indicate that the film remains room-temperature ferromagnetism and it declines slightly after Si co-doping. However, room-temperature Hall measurements indicate that the electrical property of the film improves distinctly compared with GaMnN. Cathode luminescence (CL) measurements show an obvious enhancement in luminous property and different peak strength changes at three different positions. Therefore, we demonstrate that Fermi level and the electron structure of Mn atoms will change with variation of the impurities co-doped and the intrinsic defects and this may be related with room-temperature ferromagnetism and the other corresponding properties of the film. [ABSTRACT FROM AUTHOR]

AlN layer was grown as interlayer between undoped GaN and Mg doped Al0.14Ga0.86N/GaN superlattices (SLs) epilayer to modulate the strain distribution between Al0.14Ga0.86N barrier and GaN well layers in SLs sample. Strain relaxation was observed in the SLs sample with AlN interlayer by x-ray diffraction reciprocal space mapping method. The measured hole concentration of SLs sample with AlN interlayer at room temperature was over 1.6×1018 cm-3 but that was only 6.6×1016 cm-3 obtained in SLs sample without AlN interlayer. Variable temperature Hall-effect measurement showed that the acceptor activation energy decreased from 150 to 70 meV after inserting the AlN layer, which indicated that the strain modulation of SLs induced by AlN interlayer was beneficial to the Mg acceptor activation and hole concentration enhancement. [ABSTRACT FROM AUTHOR]