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A 392 nm GaInN-based UV light emitter has been demonstrated by homoepitaxial growth technique aiming to improve quantum efficiency by crystalline perfection of the heterostructures on naturally stable semipolar (11–22) bulk GaN.

In this study, we characterized the structural defects in blue and green GaInN/GaN LEDs grown on c-plane bulk GaN and sapphire substrates. Low density large V-defects with diameters around 600 nm were found in the blue LEDs on bulk GaN. They were initiated by edge-type threading dislocations (TDs) around the homoepitaxial growth interface. On the other hand, a high density 7×109 cm−2 of smaller V-defects with sidewalls on {1101} facets was observed in the active region of green LEDs on sapphire. Their diameter ranges from 150 to 200 nm. Misfit dislocations (MDs) generated in the quantum wells are found to initiate these V-defects. With optimizing the epitaxial growth conditions, the generation of MDs and their smaller V-defects was largely suppressed. As a result, the light output power improved by one order of magnitude. For green LEDs on bulk GaN, another unique type of defect was found in the active region: an inclined dislocation pair (IDP). In it a pair of dislocations propagate at a tilt angle of 18 to 23° from the [0001] growth direction towards 100>. This defect seems to be a path of strain relief in the high indium composition quantum wells.

Characterization of operational AlGaInN heterostructure light emitting diodes (LEDs) is critical to their performance optimization and time-to-failure analysis. Typically, device performance data needs to be corroborated with structural information such as layer thicknesses, charge profiles, and the absolute location of the pn-junction. Here, non-destructive testing by capacitance-voltage profiling is being applied to AlGaInN LED structures. Within a large set of samples with different active layer geometry, we observe distinct layers of high mobile charge accumulation. We correlate those with layer thicknesses derived from an x-ray diffraction analysis of the corresponding epiwafers. In this way, we identify the charge maxima as the upper and lower interfaces of the p-type AlGaN electron blocking layer to the neighboring GaN layers. By means of this successful analysis, we now have the opportunity to monitor epi process performance and stability as well as device degradation progress quasi-continuously over the device lifetime in a non-destructive mode.

With an external laser excitation, the electroluminescence (EL) of GaInN/GaN green light emitting diodes (LEDs) grown on sapphire by metal organic vapor phase epitaxy has been investigated. The EL was found significantly enhanced under this bias and the difference can not merely be attributed to additional photoluminescence (PL). Under 325 nm photon bias, the EL enhancement starts at its highest value and decreases along with an increase of the LED current. Under 408 nm and 488 nm bias, it increases first to a value smaller than that of the 325 nm bias and then decreases with a much lower rate along the current increase. The EL enhancement is attributed to the more efficient carrier injection into quantum wells (QWs) resulting from the screening of the QW polarization by photon bias. Therefore, an enhanced balance of majority and minority carriers was obtained resulting in a better radiative recombination rate. Meanwhile, the current-voltage characteristics show a negative current first and then a voltage reduction as forward voltage increases. The reverse photocurrent indicates carrier loss due to the solar cell effect in our LED device while at high current region the carrier loss is attributed to another effect controlled by the external electrical field. At the balance point of those two effects, the EL enhancement is the highest. These findings clarify the transition from highly efficient radiative recombination at low current density to the region of efficiency droop at high current densities.

GaInN based light emitting diodes (LEDs) play an important role as energy efficient light sources in solid state lighting. A controversial discussion addresses the origin of lateral light emission variations and their correlation with either of the identified defects, e.g., threading dislocations and V-defects. In order to establish any possible correlation of defects and luminescence centers, we analyze three UV, blue and green LED dies by microscopic mapping of spectroscopic cathodoluminescence and secondary electrons at variable low temperature from 7 K to room temperature. Particular effort is being placed on a quantitative analysis of the luminescence signal. Image intensities are not being scaled and offset for highest contrast as otherwise typical for imaging mode. In standard configuration, we analyze image areas of (0.037 mm)2 with pixel resolution of 72 nm. Following regions of strong and weak emission we find that remain bright and dark respectively even at low temperature. Those variations increase with the mean emission wavelength of the LEDs and with temperature. The largest peak wavelength variation associated with the intensity contrast was observed in the green LEDs and amounts to 5 nm. Here the peak wavelength is higher in the dark spots than in the bright ones. This finding corresponds to the general trend when comparing the lower efficiency in longer wavelength green emitters to the blue ones.