Nonradiative loss processes are a major concern in nitride-based light emitting devices. Utilizing optical gain measurements on GaInN/GaN/AlGaN laser structures, we have studied the dependence of the total recombination rate on excess carrier density, up to rather high densities. From a detailed quantitative analysis, we find a room-temperature Auger recombination coefficient of 1.8 ± 0.2 × 10−31 cm6/s in the bandgap range 2.5 − 3.1 eV, considerably lower than previous experimental estimates. Thus, Auger recombination is expected to be significant for laser diodes, while it is not likely to be a major factor for the droop observed in light-emitting diodes.

An extensive analysis of the degradation characteristics of AlGaN-based ultraviolet light-emitting diodes emitting around 265 nm is presented. The optical power of LEDs stressed at a constant dc current of 100 mA (current density = 67 A/cm2 and heatsink temperature = 20 °C) decreased to about 58% of its initial value after 250 h of operation. The origin of this degradation effect has been studied using capacitance-voltage and photocurrent spectroscopy measurements conducted before and after aging. The overall device capacitance decreased, which indicates a reduction of the net charges within the space-charge region of the pn-junction during operation. In parallel, the photocurrent at excitation energies between 3.8 eV and 4.5 eV and the photocurrent induced by band-to-band absorption in the quantum barriers at 5.25 eV increased during operation. The latter effect can be explained by a reduction of the donor concentration in the active region of the device. This effect could be attributed to the compensation of donors by the activation or diffusion of acceptors, such as magnesium dopants or group-III vacancies, in the pn-junction space-charge region. The results are consistent with the observed reduction in optical power since deep level acceptors can also act as non-radiative recombination centers.

We report on the optical properties of m-plane GaInN/GaN quantum wells (QWs). We found that the emission energy of GaInN QWs grown on m-plane SiC is significantly lower than on nonpolar bulk GaN, which we attribute to the high density of stacking faults. Temperature and power dependent photoluminescence reveals that the GaInN QWs on SiC have almost as large internal quantum efficiencies as on bulk GaN despite the much higher defect density. Our results indicate that quantum-wire-like features formed by stacking faults intersecting the quantum wells provide a highly efficient light emission completely dominating the optical properties of the structures. V C 2011 American Institute of Physics. [doi:10.1063/1.3607301] In the past few years, GaN-based light emitting devices grown on non-polar planes have continuously attracted increasing attention due to their promising optical properties. While conventional structures grown on the polar c-plane suffer from the quantum-confined Stark effect (QCSE), 1 GaN layers grown on non-polar surfaces are free from polarization fields in growth direction. 2 The increased transition probability may result in an improved device efficiency leading to increased light output powers and/or reduced threshold current densities. 3 Indeed, the first GaInN based laser diodes with an emission wavelength at 500 nm have been shown by Okamoto et al. on m-plane GaN substrates. 4 However, up to now, non-polar GaN substrates are still barely available, small in size, and also very expensive. As an alternative, several groups have reported heteroepitaxial growth of non-polar GaN layers on foreign substrates (c-LiAlO 2 , SiC, r-plane sapphire). [5][6][7] However, most of these structures were affected by high densities of threading dislocations (TDs) and basal plane stacking faults (BSFs), which are terminated by either prismatic stacking faults (PSFs) or partial dislocations. 8 While TDs are known to act as nonradiative recombination centers, BSFs are optically active since they can be considered as cubic (zincblende) ABC phases in the wurtzite ABAB stacking sequence. Such a structure forms a type-II heterojunction which may capture electrons and holes resulting in optical transitions below the wurtzite GaN bandgap energy. 9-11 More recently, a BSF related emission from aplane GaN/AlGaN quantum well (QW) structures was reported, suggesting the formation of quantum-wire-like states in the regions where BSFs intersect the QWs. 12,13 In this paper, we investigate the optical properties of m-plane GaInN/GaN QW structures grown on silicon carbide (SiC). In particular, we show that stacking faults intersecting the QWs dominate the optical properties of these structures.Our samples were grown on m-plane 6H-SiC, m-plane bulk GaN substrates, and a-plane GaN templates (grown by hydride vapor phase epitaxy) in a low pressure metalorganic vapor phase epitaxy system with a horizontal reactor (Aixtron AIX 200RF). The precursors used were trimethylgallium, triethylgallium, trimethylaluminum, trimethylindium,...

We present Schottky type metal semiconductor metal (MSM) AlGaN photodetectors (PDs) suited for the ultraviolet C (UV‐C) spectral region grown on conventional planar AlN templates in comparison with epitaxial laterally overgrown (ELO) AlN templates. On planar templates solar blind MSM PDs with state‐of‐the‐art dark current in the pA range and a power independent responsivity are obtained. Using ELO templates with sapphire substrates tilted to the m direction the defect density in the absorber material is reduced compared to that for planar templates. The MSM PDs on this ELO templates exhibit photoconductive gain leading to external quantum efficiencies of up to 77 at 30 V applied bias surpassing that of the planar grown PDs by a factor of 100. In spite of the high gain these PDs also show low dark currents in the pA range up to 100 V applied bias, short switching times and two operating regimes with power independent responsivity. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The optical gain of single quantum well laser structures on semipolar (1122)-GaN in dependence of the optical polarization and the resonator orientation has been studied by variable stripe length method. The c'-[1123] resonator shows maximum gain in TE mode, followed by the m-[1100]-resonator with extraordinary polarization. The anisotropic gain behaviour is explained by valence sub-band ordering and birefringence of the wurtzite crystal, resulting in a modification of the transition matrix element for stimulated emission. Measurements are accompanied by 6 x 6 k . p band structure calculations and gain analysis