Degradation Of InGaN-based Laser Diodes Research Articles

Impact of dislocations on DLTS spectra and degradation of InGaN-based laser diodes

The aim of this paper is to illustrate the dependence of DLTS characteristics and degradation of InGaN-based laser diodes (LDs) on the density of dislocations. Three groups of multi-quantum well LDs with different dislocation densities were submitted to constant current stress, at room temperature: the analysis is based on combined electrical-optical measurements and Deep-Level Transient Spectroscopy (DLTS) investigation was made before and after stress. DLTS results show the presence of a hole trap in all the samples, whose intensity is related to the dislocation density. Constant current stress induces a significant decrease in the optical power (subthreshold regime), not related exclusively to the dislocation density, and the appearance of a new deep level for electrons (point defect generated after stress).

Long-term degradation of InGaN-based laser diodes: Role of defects

The aim of this paper is to give an extensive presentation of the defect-related degradation of InGaN-based laser diodes (LDs) submitted to constant current stress, at room temperature. The analysis is based on combined electrical-optical characterization, the capacitance-temperature analysis, and deep-level transient spectroscopy (DLTS). The results show that stress induces a significant increase of the threshold current and the appearance of two defects, possibly related to point defects arranged along lines.

Thermally-activated degradation of InGaN-based laser diodes: Effect on threshold current and forward voltage

This paper presents a study of the effects of high temperature stress on the electro-optical characteristics of violet InGaN-based laser diodes. The results indicate that: (i) when submitted to constant current stress (with relatively high junction temperatures), devices show a significant increase in threshold current (Ith), related to the increase in non-radiative recombination; micro-cathodoluminescence measurements indicate that the area affected by degradation is wider than the ridge; (ii) the results of purely-thermal stress test indicate that the exposure to high temperature may induce an increase in threshold current; (iii) during the first part of the stress, this mechanism is well correlated with the variation of the forward voltage, suggesting a degradation in the properties (conductivity, acceptor doping) of the p-type material; for longer stress times, a further Ith increase is detected, with a linear dependence on time.

Investigation of the deep level involved in InGaN laser degradation by deep level transient spectroscopy

This paper reports an extensive analysis of the properties of the deep level responsible for the degradation of InGaN-based laser diodes. The analysis is based on combined optical measurements and Deep-Level Transient Spectroscopy (DLTS) investigation. Results indicate that stress induces a significant increase in threshold current of the devices, which is strongly correlated to the increase in the concentration of a deep level (DL) detected by DLTS. The DL involved in the degradation process is located 0.35–0.45 eV below the conduction band. 2D simulation indicates that degradation occurs within the quantum-well region.

Degradation of InGaN lasers: Role of non-radiative recombination and injection efficiency

With this paper we propose a detailed study of the gradual degradation of InGaN-based laser diodes and Light-Emitting Diodes submitted to electro-thermal stress. The two device structures have been processed from the same epitaxial wafer. Our purpose is to compare the behavior of the two devices by means of electro-optical measurements, electroluminescence characterization, and near field emission measurements. We demonstrate that: (i) stress induces a decrease in the optical power and an increase in threshold current; (ii) the two failure modes are strictly linked each other, and correlated to the increase in defect-related current components, indicating a substantial increase in defect density during degradation; (iii) analysis of characteristic temperature and near-field emission measurements do not indicate any strong variation of injection efficiency nor current confinement of the devices.

Degradation of InGaN-based laser diodes analyzed by means of electrical and optical measurements

In this paper we present a detailed analysis of the degradation of InGaN-based laser diodes carried out by means of electrical and optical techniques. The study is based on the comparison between the degradation kinetics of laser diodes and light-emitting diode (LED)-like samples, i.e., devices with the same epitaxial structure as the lasers, but with no ridge and facets. Results described in the following indicate that degradation of lasers and LED-like samples is due to the same mechanism, possibly involving the generation of point defects within the active region of the devices. Furthermore, since degradation occurs both in lasers and in LED-like samples (i.e., structures with no current confinement), results suggest that degradation of lasers is not correlated with the geometry of the devices, nor to worsening of current confinement under the ridge.

Degradation of InGaN-Based Laser Diodes Related to Nonradiative Recombination

We present a detailed study of the degradation of InGaN-based laser diodes submitted to electrical stress tests, which is aimed at understanding the role of nonradiative recombination in determining the worsening of the properties of the devices. The analysis, which is carried out by means of optical techniques, indicates that stress determines an increase in the threshold current of the devices without strong modifications in the slope efficiency. For the first time, we give an experimental demonstration of the fact that the threshold current increase is correlated to the increase in the nonradiative recombination rate of the carriers in the active layer. This result has been verified in a wide range of operating current levels; furthermore, the results of stress tests carried out at different current levels support the hypothesis that current is a significant driving force for the analyzed degradation process.

Analysis of the Role of Current, Temperature, and Optical Power in the Degradation of InGaN-Based Laser Diodes

This paper reports on the degradation of InGaN-based laser diodes for Blu-ray technology. The devices have been submitted to stress under: 1) constant current, different temperatures; 2) high temperature, no bias; and 3) constant temperature, several current levels. The tests carried out within this paper demonstrate that stress determines the increase in the threshold current, according to the square root of stress time. The degradation rate has been found to be strongly determined by the stress current level, while the optical field had only a limited role in determining the degradation kinetics. The impact of temperature on device degradation is also limited, as confirmed by the activation energy value of 250 meV extrapolated by measurements carried out at different temperatures. On the basis of the evidence collected within this paper, we attribute the degradation of the lasers to an electrothermally activated process that induces an increase in the nonradiative recombination rate with subsequent decrease in the optical efficiency of the active layer.

Extensive Analysis of the Degradation of Blu-Ray Laser Diodes

This letter describes an analysis of the degradation of InGaN-based laser diodes. The influence of current, temperature, and optical power level on the degradation kinetics has been analyzed by means of a wide set of stress tests carried out under different operating conditions. We demonstrate the following: 1.) the degradation rate is strongly related to the operating current level; 2.) high-temperature stress does not determine significant degradation of lasers characteristics; and 3.) the intensity of the optical field does not significantly influence the degradation rate. Degradation process is found to be electrothermally activated and is ascribed to the increase of the nonradiative recombination rate in the active layer, with subsequent decrease of the efficiency of the devices.