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ABSTRACT: GaxIn1–xN/GaN single quantum well (QW) structures emitting in the range of 450 nm to 620 nm have been grown by MOVPE. Temperature and excitation power dependent photoluminescence (PL) was used to determine the internal quantum efficiency (IQE) for these structures. For the blue emitting QWs high IQE values on the order of 60% were achieved. Due to a reduced growth temperature, reduced growth rate and increased V/III ratio we obtained QWs with good morphology and high In content above 25%. Thinner QWs with high In content showed a clear improvement of IQE compared to QW-structures with larger thickness but smaller In-content emitting at the same wavelength. Between λpeak = 460 nm and 530 nm we observed a slight reduction in IQE with values of 58% at 490 nm and 40% at 525 nm. But towards λpeak = 620 nm IQE decreased due to the electric field induced separation of the electron and hole wavefunction down to 1%. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 05/2006; 3(6):1966 - 1969.
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ABSTRACT: We have achieved dramatic improvement of the internal quantum efficiency (IQE) for ultraviolet-emitting GaN/AlGaN quantum-well (QW) structures. Despite a defect density of a few 109 cm−2 and the use of an In-free QW we achieve best values for the IQE at room temperature of 26%. Under strong nonresonant excitation, the IQE even increases to 38%. We observe a weak dependence of the IQE on excitation power for our structures. This indicates that similar mechanisms as for GaInN-based light emitters are present.
Applied Physics Letters 05/2006; 88(19):191108-191108-3. · 3.84 Impact Factor
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ABSTRACT: We have optimized the internal quantum efficiency (IQE) of Ga In N / Ga N quantum-well (QW) structures. For an emission wavelength of 460 nm , a high IQE of 73% was achieved. For a longer emission wavelength, calculations predict higher oscillator strength for thinner QWs but higher In content. We observe an improvement in IQE of almost 50% when reducing the QW width from 2.7 nm to 1.8 nm , and increasing the In content for the whole blue to green spectral region with IQE =40% at 525 nm . The typical saturation of the output power with increasing current that occurs, particularly for green-light-emitting diodes, is extremely weak in our structures.
Applied Physics Letters 03/2006; · 3.84 Impact Factor
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ABSTRACT: Despite the high density of threading dislocations generally found in (AlGaIn)N heterostructures, the light emission efficiency of such structures is exceptionally high. It has become common to attribute the high efficiency to compositional fluctuations or even phase separation in the active GaInN quantum well region. The resulting localization of charge carriers is thought to keep them from recombining nonradiatively at the defects. Here, we show that random disorder is not the key but that under suitable growth conditions hexagonal V-shaped pits decorating the defects exhibit narrow sidewall quantum wells with an effective band gap significantly larger than that of the regular c-plane quantum wells. Thereby nature provides a unique, hitherto unrecognized mechanism generating a potential landscape which effectively screens the defects themselves by providing an energy barrier around every defect.
Physical Review Letters 10/2005; 95(12):127402. · 7.37 Impact Factor
