Masaaki Yuri

600 mW CW single-mode GaAlAs triple-quantum-well laser with a new index guided structure

A very-high-power, single-mode GaAlAs triple-quantum-well (TQW) laser with a novel real refractive index guided structure has been developed. The maximum output power of 720 mW CW and single transverse- and longitudinal-mode operation up to 600 mW CW have been achieved in a single-element device. This excellent mode operation is attained by using the real refractive index guided structure with a GaAlAs current-blocking layer which gives a low effective refractive index step, suppressing the spatial hole-burning effect in the high-power range. >

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.

Analysis of Diffusion-Related Gradual Degradation of InGaN-Based Laser Diodes

This report reveals that diffusion of hydrogen induces gradual degradation in InGaN-based laser diodes (LDs). The increase in nonradiative recombination centers (NRCs) in the LDs has been attributed to diffusion-related phenomena. Factors other than NRCs, such as the threshold carrier density Nth, can increase threshold current Ith. Those factors, however, were not fully investigated. Moreover, the diffusant responsible for the degradation of the LDs has not been univocally identified yet. To separately evaluate the roles of NRCs and Nth in increasing Ith, this report analyzes the stress-induced variation of nonradiative recombination lifetime τnr and lasing wavelength λl. It is revealed that the density of NRCs increases at the first stage of gradual degradation, followed by a rise in Nth. In addition, this report proposes a novel model for the time-variation of 1/τnr to investigate the diffusion-related degradation. By using this model, we extrapolate the value of the diffusion coefficient of diffusants involved in the degradation in InGaN-based LDs. The proposed analysis methods and obtained results are useful for understanding the physics of LD degradation.

100-mW high-power angled-stripe superluminescent diodes with a new real refractive-index-guided self-aligned structure

We have developed 100-mW high-power angled-stripe superluminescent diodes with a new angled-stripe real refractive-index guided self-aligned structure. The structure has a GaAlAs optical confinement layer on a planar active layer and an inclined current injection stripe by 5/spl deg/ with respect to the facet normal. The structure gives small internal loss (/spl sim/10 cm/sup -1/) and facet power reflectivity less than the order of 10/sup -6/. As a result, the output power as high as 105 mW at a low operating current of 270 mA is obtained with less than 3% spectral modulation and 10.5 nm full width at half maximum (FWHM) spectral width.

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.

A review on the reliability of GaN-based laser diodes

University of Padova in collaboration with Panasonic Corp. has developed in the recent years an in depth reliability analysis of Blu-Ray InGaN Laser Diodes (LD) submitted to CW stress at different driving conditions. The reliability analysis has been focused towards a) the identification of the effects of current, temperature and optical field and b) the identification of the physical mechanism related to degradation. Results show that LD devices exhibit a gradual threshold current increase, while slope efficiency is almost not affected by the ageing treatment. Degradation rate is found to depend on stress temperature and on current level, while it does not significantly depend on the optical field in the cavity. Within this paper we demonstrate that: (i) the degradation rate shows a linear correlation with stress current level; (ii) the Ith increase is correlated to the decrease in non-radiative lifetime (τ nr ); (iii) stress temperature acts as an accelerating factor for LD degradation; (iv) pure thermal storage does not significantly degrade LDs characteristics.

Low operating current and high-temperature operation of 650-nm AlGaInP high-power laser diodes with real refractive index guided self-aligned structure

Low operating current and high-temperature operation has been demonstrated in 650-nm AlGaInP high-power laser diodes with real refractive index guided self-aligned (RISA) structure. The RISA structure features an Al/sub 0.5/In/sub 0.5/P current blocking layer, which leads to small internal loss in the waveguide and substantially reduced operating carrier density. The resultant operating current for 50-mW continuous-wave at 70/spl deg/C is as low as 98 mA, which is almost a half of the lowest value ever reported.

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.

Reliability analysis of InGaN Blu-Ray laser diode

Abstract The purpose of this work is an in depth reliability analysis of Blu-Ray InGaN laser diodes (LD) submitted to CW stress at different currents and temperatures. During reliability tests, LD devices exhibit a gradual threshold current increase, while slope efficiency is almost not affected by the ageing treatment. Furthermore we demonstrate that: (i) the degradation rate shows a linear correlation with stress current level; (ii) the I th increase is correlated to the decrease in non-radiative lifetime ( τ nr ); (iii) stress temperature acts as an accelerating factor for LD degradation; (iv) pure thermal storage does not significantly degrade LDs characteristics.

Analysis of diffusion involved in degradation of InGaN-based laser diodes

The gradual increase in threshold current in InGaN-based blue laser diodes (LDs) submitted to stress tests is generally attributed to diffusion-related phenomena. In fact, diffusion into active layers can increase the concentration of non-radiative recombination centers (NRCs). However, this hypothesis has not been verified yet for InGaN LDs. In this paper, we analyze the variation of the non-radiative recombination lifetime τnr in LDs submitted to stress tests: the analysis of τnr provides information on the density evolution of NRCs. Furthermore, we propose a novel model for the investigation of the degradation kinetics. This model assumes that the depth distribution of NRCs obeys to Ficks diffusion equation. The obtained results suggest that the increase in 1/τnr can be correlated to a diffusion process. For the first time, we have estimated the value of the diffusion coefficient that is related to degradation, which is equal to 1.9×10−19 cm2/sec. This value is very large if compared with the one obtained in bulk material. Therefore, we suggest that the diffusion process is driven by the presence of dislocations. The presented method for degradation analysis constitutes a powerful tool for the study of the degradation in InGaN-based LDs.