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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.

High-power InGaN-based laser diodes (LDs) are expected as light-sources of various high-power applications. The catastrophic-optical-damage (COD) is a major failure mechanism to limit the output power, where optical absorption at a light-emitting facet causes an irreversible damage to the LDs. In this paper, a window structure in InGaN-based LDs to suppress the COD is demonstrated for the first time. The structure is formed by the metal organic chemical vapor deposition growth over a recess placed besides of the ridge-waveguide. The In composition in the quantum well which is corresponding to the bandgap energy is reduced by controlling the local tilt angle at the sidewall of the recess. Thus, the formed window structure eliminates undesired optical absorption at the cleaved facet so that extremely high light output power over 2 W in narrow-stripe ridge-waveguide InGaN-based blue-violet LDs is achieved without any CODs.

This report describes a crystallization method we developed for amorphous (a)-Si film by using 405-nm laser diodes (LDs). The proposed method has been used to fabricate bottom gate (BG) microcrystalline (µc)-Si TFTs for the first time. A µc-Si film with high crystallinity was produced and high-performance BG µc-Si TFTs with a field effect mobility of 3.6cm2/Vs and a current on/off ratio exceeding 108 were successfully demonstrated. To determine the advantages of a 405-nm wavelength, a heat flow simulation was performed with full consideration of light interference effects. Among commercially available solid-state lasers and LDs with wavelengths having relatively high optical absorption coefficients for a-Si, three (405, 445, and 532nm) were used in the simulation for comparison. Results demonstrated that wavelength is a crucial factor for the uniformity, efficiency, and process margin in a-Si crystallization for BG µc-Si TFTs. The 405-nm wavelength had the best simulation results. In addition, the maximum temperature profile on the gate electrode through the simulation well explained the actual crystallinity distributions of the µc-Si films.

With this paper we analyze the correlation between the degradation of InGaN-based laser diodes (LDs) and the increase in the non-radiative recombination rate in the active region. Several 405 nm MOCVD LDs have been submitted to CW stress, for 2000 h (stress current in the range 40-100 mA, case temperature = 75 °C). During stress, we extensively evaluated the optical characteristics of the LDs: a technique for the evaluation of the non-radiative recombination lifetime (τ nr ) in the active material was developed and used for the analysis of the stress effects. We demonstrate the following: (1) degradation determines the increase in LDs threshold current (I th ) and the decrease in the τ nr ; (2) degradation of I th and τ nr have similar kinetics; and (3) the degradation rate of the LDs is almost linearly related to the stress current level. The degradation process is therefore ascribed to the decrease of internal quantum efficiency caused by the increase of the non-radiative recombination rate in the active region.

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.

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.

This paper reports on high-power and high-temperature operation of an AlGaInP-based high-power red laser diode with magnesium (Mg)-doped quaternary-alloy cladding layer. The use of Mg dopant with small diffusion coefficient enables abrupt doping profiles as well as high carrier concentrations when compared to conventional zinc (Zn) dopant. It was also found that the metal-organic vapor phase epitaxial (MOVPE) growth of Mg-doped quaternary AlGaInP alloy is not affected by so-called reactor memory effects, while unintentional incorporation of Mg is observed in GaAs after the growth of Mg-doped GaAs layers. The higher carrier concentration in the p-type cladding layer enhanced carrier confinement in the active layer so that device performance at high temperature is improved. The abrupt doping profile suppressing dopant diffusion into the active layer eliminates the nonradiative recombination in the active layer resulting in higher external quantum efficiency. The characteristic temperature of the Mg-doped red laser with a lasing wavelength of 659 nm is as high as 167 K while the Zn-doped laser exhibits a temperature of 127 K. High kink-free output power of 150 mW is achieved at 75/spl deg/C.

A vertical InGaN-based blue light emitting diode (LED) with a reflective metal electrode and thick gold plated base free from insulating sapphire is demonstrated. A 50 μm-thick gold plated layer on a highly reflective platinum p-side ohmic contact is formed on the InGaN-based LED epi-structure, followed by irradiation with high power ultra-violet pulsed laser from the backside of the original sapphire substrate. The laser processing, so called laser lift-off technique, enables the separation of sapphire by decomposition of interfacial GaN layer. No transparent electrode is necessary for the LED because the current can spread well through the highly conductive n-GaN layer so that uniform blue light is emitted through the n-GaN layer. The electroluminescence (EL) spectra show small multi peaks due to the resonance within the formed vertical cavity. In addition, the measured thermal resistance of the vertical LED is smaller than that of the conventional LED on poor heat-conductive sapphire. The vertical LED would increase the brightness together with smaller chip size and lower series resistance. This would be advantageous espacially for high power and highly efficient LEDs applicable to future solid state lighting. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A very thin 1 μm-thick Al 0.11 Ga 0.89 N film is successfully separated from a sapphire substrate by thermal decomposition of interfacial region using high power laser, so-called laser lift-off technique. The used layer structure prior to the separation is 1.0 μm Al 0.11 Ga 0.89 N/0.3 μm GaN on sapphire grown by metal organic chemical vapor deposition (MOCVD), and third harmonic Q-switched Nd:YAG laser ( λ =355 nm) is irradiated from the backside of the sapphire. Absorption of the laser light occurs only at the GaN interlayer and the decomposed thickness is limited up to the interlayer thickness. As a result, a crack-free thin AlGaN film is separated from sapphire with metal Ga underneath through the optimization of the process parameters. In contrast, removal of 2 μm-thick GaN single layer from sapphire is also tested, where peeling-off of the film with cracks is seen. In addition, slight red shift of the peak energy in the cathodoluminescence (CL) spectra of the AlGaN film is observed after the lift-off process, which is due to the relaxation of compressive stress in the film. Thus, separated AlGaN film is free from the disadvantages of using sapphire substrates such as the thermal mismatch, higher series resistance and poor heat dissipation so that it would enable high performance AlGaN-based ultraviolet (UV) light emitters.

We demonstrate highly efficient frequency doubling of a 160 mW-AlGaAs three-section tunable distributed Bragg reflector (DBR) laser diode with real refractive-index-guided structure in a quasi-phase-matched second harmonic generation (QPM-SHG) ridge-type waveguide device. We realized high coupling efficiency of the DBR laser diode and the QPM-SHG waveguide device using a planar-type butt-coupling configuration. High-power SHG blue violet laser was fabricated, whose volume is 0.3 cc. This SHG blue-violet laser satisfied the several specifications for optical disk systems, and the pulsed blue-violet light (410 nm) power of 62 mW was generated.

780 nm-band AlGaAs and 650 nm-band AlGaInP laser diodes are monolithically integrated on a GaAs substrate as the light source in DVD/CD optical pickups. In order to reduce internal losses for improved characteristics and to ensure better flexibility of device design, real-refractive index-guided self-aligned (RISA) structure is employed for both 780 nm and 650 nm-band LDs. As a result, low noise characteristics due to self-sustained pulsation in the both wavelength bands have been achieved. A dual-wavelength laser with a high power ( > 100 mW) 780 nm-band LD has also been developed for recording of CD-R/RW disks.

Group-III (B, Al, Ga, and In)-nitride quaternary alloys and group-III (Al, Ga, and In)-nitride-based mixed anion (As, P, and Sb) quaternary alloys are useful for blue and green light emitting devices and high-temperature, high-power, and high-frequency electronic devices. It is known that these alloys are very difficult to grow in certain compositional regions. The thermodynamical stability of these alloys is studied with respect to an unstable two-phase region in the phase field. The unstable two-phase region is predicted based on a strictly regular solution model. The interaction parameter used in our model is obtained analytically using the valence force field (VFF) model modified for wurtzite structures. The calculated interaction parameters, which are required to predict the unstable two-phase region, agree well with experimental results for related alloy systems. The modified VFF model can also be used to predict the microscopic crystal structure, such as first neighbor anion–cation bond lengths. In...

A model to predict material characteristics of the InGaN ternary system, which is useful for blue and green light emitting and laser diodes, with respect to an unstable two-phase region in the phase field and the first neighbor anion–cation bond length is developed. The unstable region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field (VFF) model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in GaN and InN is also taken into account in our model. The critical temperatures found in our analysis for wurtzite InGaN and zinc-blende InGaN are 1967 and 1668 K, respectively. This suggests that, at typical growth temperatures around 800 °C, a wide unstable two-phase region exists in both wurtzite and zinc-blende structures. The modified VFF model can also predict the microscopic crystal structure, such as first neighbor anion–cation bond lengths. In order to validate our calculation results for zinc-blende structures, we compare the calculated and the experimental results in terms of the interaction parameter and the first neighbor anion–cation bond lengths in the InGaAs system. For the wurtzite structure, we compare the calculated and the experimental results for the first neighbor anion–cation bond lengths in the InGaN system. The calculated results agree well with the experimental results.

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.

Nitridation process of a sapphire surface was investigated with atomic force microscopy (AFM), reflection high-energy electron diffraction (RHEED), and X-ray photoelectron spectroscopy (XPS) in order to reveal a general nitridation mechanism. It was found that the nitridation process consists of two steps. First, inter-mixing between nitrogen-related species and sapphire surface occurs forming hydrogenated Al oxynitride. This step does not change the surface morphology significantly. Second, crystalline AlN islands are gradually formed by further nitridation of hydrogenated Al oxynitride, resulting in a very rough surface.

High crystalline quality thick GaN films were grown by vapor phase epitaxy using GaCl3 and NH3. The growth rate was in the range of 10~15 Μm/h. GaN films grown at higher temperatures (960~ 1020‡C) were single crystalline with smooth surface morphologies. No chlorine impurity was incorporated in these films during growth. The best crystalline quality and surface morphology of grown films was achieved by sputtering a thin A1N buffer layer, prior to growth. According to reflection high energy electron diffraction and atomic force microscopy measurements, as-sputtered A1N buffer layer was amorphous with root means square roughness of 0.395 nm and then crystallized during the GaN growth. This improved the GaN growth due to more uniform distribution of GaN nucleation. Rutherford backscattering channeling experiments produced the lowest value from the GaN film grown on a-Al2O3 with a 500a A1N buffer layer at 1020‡C.

Real refractive index guided self-aligned (RISA) AlGaAs laser diodes have various advantages over conventional complex refractive index guided lasers, which include low operating current, stablefundamental transverse-mode operation up to high power levels, good controllability of current and optica distributions, and so on. In this review, the concept of RISA lasers and their applications to optical data storage systems are presented. Taking advantage of low operating current characteristics of the RISA lasers, a number of optical elements which compose a conventional optical pickup are successfully integrated into a very small plastic package, which results in substantial reduction of pickup size in various optical disk systems.

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.

Self-sustained pulsation in narrow stripe geometry AlGaAs laser diodes is investigated numerically and experimentally. By taking account of the time-dependent two-dimensional optical field, carrier spreading in the cladding layers, and multilongitudinal modes, we succeeded in clarifying the mechanism for the pulsation. Fluctuation of the optical field plays an important role in forming saturable absorption. The numerical analysis clearly shows that our newly proposed real refractive index-guided structure is very suitable for a pulsation laser in which the optical field distribution and current spreading can be independently controlled. Furthermore, me show that the new structure gives much lower threshold current than that of a conventional loss-guided structure. These predicted advantages of the real refractive index-guided structure are verified experimentally with good agreement. >

We have developed a high-power self-sustained pulsation laser by using a multiple-quantum-well real refractive index guided self-aligned (RISA) structure that allows formation of large saturable absorbers outside a stripe region. As a result, a peak power as high as 800 mW was obtained in the laser with the stripe width of 1.0 /spl mu/m. >

A 405 nm LDs crystallization method of a-Si has been applied to the processing of bottom gate (BG) type microcystalline (μc-) Si TFT for the first time. We have successfully demonstrated superior I-V characteristics of BG μc- Si TFTs. In order to verify the validity of our process, we performed a heat flow simulation and compared commercially available lasers having wavelengths of 405, 445 and 532 nm. The simulation explained well the experimental results and showed that the wavelength is a crucial factor on uniformity, energy efficiency, and process margin and the 405 nm gave the best results among the three wavelengths.

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. >

High power over 2W free from catastrophic-optical-damage is achieved in InGaN-based lasers with epitaxially-formed window structure. Epitaxial growth over a recess reduces the In composition which eliminates the undesired optical absorption only at the facet.

With this paper we describe an extensive analysis of the reliability of InGaN-based laser diodes, emitting at 405 nm. These devices have excellent characteristics for application in the next-generation optical data storage systems. The analysis aims at describing the degradation process, as well as at investigating the role of current in determining the degradation rate. The results obtained within this paper suggest that the degradation of the laser diodes is correlated to the increase in the non-radiative recombination rate, with subsequent worsening of the optical properties of the devices. Furthermore, our findings support the hypothesis that current is the main driving force for degradation, while temperature and optical power play only a limited role in determining the degradation kinetics.

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 τ nr in LDs submitted to stress tests: the analysis of τ nr 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 Fick's diffusion equation. The obtained results suggest that the increase in 1/τ nr 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.

A novel high-power GaAlAs superluminescent diode (SLD) structure that introduces an antireflective (AR) window region into the rear side of the SLD is proposed. The light beam which travels backward is emitted from the edge of the active layer and diverges in the window region. Then the beam is reflected at the AR-coated rear facet only by a small percentage, a fraction of which couples into the active layer. Thus, this window structure gives a reduction of the reflectivity at the interface between the active layer and the window region so that lasing oscillation is successfully suppressed. An SLD operation of output power as high as 50 mW is obtained with a stable fundamental spatial mode. The spectral bandwidth at half maximum is about 15 nm over a wide output power range. >

This paper reports an analysis of the degradation of laser diodes for Blu-Ray technology. The study has been carried out by means of optical and electrical characterization techniques. We demonstrate that: (i) stress at constant current level determines the increase of the threshold current of the devices, and the decrease of the sub-threshold emission signal; (ii) degradation rate has an almost linear dependence on the stress current level, thus suggesting that current is a significant driving force for devices degradation. Furthermore, thanks to an accurate study of the optical parameters of the devices, we demonstrate that the degradation of the samples is due to the decrease of the non-radiative recombination lifetime of the carriers in the active layer, with subsequent decrease of the optical efficiency of the devices. Degradation can be attributed to the generation/propagation of defects in the active layer of the devices, that can be also responsible for the modification of the electrical parameters of the laser diodes.

It is generally speculated that the increase of threshold current Ith in GaN-based blue laser diodes (LDs) during aging is caused by the increase of nonradiative recombination centers in the InGaN MQW active layers. However, no reports directly supported this speculation. In this report, by analyzing current-light output characteristics below threshold, we have proved that the nonradiative recombination lifetime decreases during degradation. The observation directly verifies that the density of defects increases during aging. The increase of Ith is mainly caused by the decrease of carrier lifetime. These results will be useful to comprehend the underlying physics on degradation in GaN-based LDs.

This paper describes an analysis of the reliability of GaN-based laser diodes, submitted to constant current, constant optical power and high temperature stress. We demonstrate that constant current and constant optical power stress induce the increase of the threshold current of the devices, that varies according to the square-root of time. The threshold current increase is found to be strongly correlated to the decrease of the sub-threshold emission of the devices, thus suggesting that stress determines the increase of the non-radiative recombination paths in the active layer. 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. The evidences presented within this work support previous literature results, that attribute devices degradation to the diffusion of impurity species towards the active layer, with subsequent increase of the non-radiative recombination rate. The identified degradation process is shown to be electro-thermally activated.

A novel GaN-based surface-emitting laser was realized by utilizing total internal reflection (TIR) by an inclined mirror formed at one end of the horizontal cavity of an edge-emitting laser. The inclined mirror was fabricated by focused ion beam (FIB) etching. The mirror was inclined by 45° with respect to the surface normal. The guided light propagating along the horizontal-cavity is reflected at the mirror to the surface normal. We analyzed optical losses in the laser. To increase the external quantum efficiency, removal of an FIB-damaged layer and precise control of the mirror angle are important. Argon-milling was applied to the FIB-etched surface to remove the FIB-damaged layer which causes an optical loss. The fabricated device with the stripe width of 8 µm and the cavity length of 600 μm lased at 390 nm with a threshold current of 260 mA. Surface-emission was obtained with beam divergence angles of 24.0° and 6.2°, corresponding to perpendicular and parallel to the junction plane, respectively. The presented surface-emitting laser is suitable to form high-power GaN-based 2D laser arrays.

This paper presents an analysis of the role of current in the long-term degradation of InGaN-based laser diodes (LDs). The analysis has been carried out by means of a wide set of stress tests under different driving conditions. During stress, the optical and electrical characteristics of the samples have been continuously monitored, with the aim of determining the physical mechanisms responsible for degradation and the dependence of the degradation rate on the driving conditions. The results reported in this paper demonstrate that: (i) constant current stress determines the increase of the threshold current of the devices, that is well related to the decrease of the sub-threshold emission; (ii) stress induces the increase of the reverse current of the devices, but does not affect their forward-bias characteristics; (iii) degradation rate has an almost linear dependence on stress current level; (iv) degradation takes place also below lasing threshold and for very low stress current levels, i.e. with very limited optical field levels. The results described in this paper indicate that the degradation kinetics are mostly determined by the stress current level used during operation: optical field and temperature are thought to play only a minor role in determining the degradation rate. Furthermore, the strong correlation between the threshold current increase and the sub-threshold emission decrease suggests that degradation can be ascribed to the increase of the non-radiative recombination rate in the active region of the devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

We have successfully attained low‐noise and high‐power operation in GaAlAs lasers by applying high reflectivity facet coating approach to nonabsorbing mirror lasers. High reflectivity coating is used to reduce feedback induced noise coming from hopping between the diode cavity modes and between the external cavity modes. A nonabsorbing mirror structure is used to obtain high‐power operation by suppressing mirror degradation and catastrophic optical damage effectively even with the use of high reflectivity coating. Nonabsorbing mirror lasers with the front facet reflectivity 50% showed the relative intensity noise level less than −130 dB/Hz at 3 mW under 0%–10% optical feedback and showed the cw output power as high as 50 mW in fundamental spatial mode operation. Under 30‐mW cw operation at 50 °C, on the other hand, obvious degradation has not been observed over 4000 h in the nonabsorbing mirror lasers with 50% front facet reflectivity. Thus the present laser is useful as a low‐noise source at a low‐power level and also as a high‐power source with high reliability.

The effects of misfit strain on physical properties (lattice parameters, photoluminescence, and electron mobility) are discussed for In1−xGaxP epilayers with a constant thickness of around 0.75 μm grown by metalorganic molecular‐beam epitaxy on GaAs(001) substrates. The elastic accommodation of misfit strain is observed in the analysis of lattice parameters and energy‐band‐gap shift. Tensile strain is relaxed more easily than the compressive strain. Theoretical predictions of critical thickness for elastic‐strain accommodation and of energy‐band‐gap shift agree well with experimental results. The energy‐band‐gap shift and electron mobility are relatively insensitive to dislocations generated by relaxation of the misfit strain.

Metalorganic molecular-beam epitaxy of InGaP, InAlP, and AlGaP was investigated at various temperatures (290–650°C), using triethylindium (TEIn), triethylgallium (TEGa), triethylaluminum (TEAl), and phosphine. Three distinct stages were observed in the temperature dependence of growth rate and epilayer composition of those ternaries. At lower temperatures below 390°C the incomplete pyrolysis of TEGa and TEAl limits the growth, while TEIn decomposes perfectly as low as 290°C. TEAl decomposition is incomplete at all the temperatures studied, and is enhanced by the existence of TEIn or TEGa. To explain this observation, a co-decomposition mechanism was proposed, in which thermal energy produced by the pyrolysis of TEIn or TEGa induces the decomposition of TEAl; complexes such as TEAl-TEIn and TEAl-TEGa are assumed to be formed by mixing the metalorganics in the vapor phase. In the moderate-temperature region of 390–520°C, the growth is limited by the supply of metalorganics. At higher temperatures above 520°C phosphorus evaporates from the superficial part of epilayers with breaking bonds of In-P, resulting in many indium droplets on the epilayer surfaces. The incorporation of gallium and aluminum atoms into the indium droplets reduces the growth rate of the GaP and AlP constituents in InGaP and InAlP epitaxy. By the absence of In-P bonds, the growth rate of AlGaP does not decrease up to 650°C, and no droplets are formed on the surfaces.

In this paper, we demonstrate Mg-doped AlGalnP LDs with high characteristic temperature. We found that abrupt Mg profiles can be obtained in quaternary alloys like AlGalnP, although significant memory effects are observed in GaAs. Based on this effect, we fabricated AlGalnP LDs with a highly Mg-doped cladding layer. As a result, reliable 650-nm-band LDs with characteristic temperature over 133 K are achieved.

High temperature self-sustained pulsation has been realized with a real refractive index guided self-aligned (RISA) structure which has a compressively strained-MQW for the active region. Self-sustained pulsation is maintained up to 75/spl deg/C at an average power of 7 mW CW and the maximum operating current is as low as 60 mA. The maximum operating temperature for self-sustained pulsation is the highest ever reported.

We demonstrate for the first time low-noise (RIN 150 mW) self-sustained pulsation GaAlAs MQW laser diodes with small-astigmatism (

Summary form only given. The structural dependence of self-sustained pulsation in AlGaAs laser diodes is quantitively analyzed for the first time, with the incorporation of the two-dimensional distribution of carriers and photons into the multi-longitudinal-mode rate equations.

We have developed for the first time 100 mW high-power angled-stripe superluminescent diodes with a new 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 facets. That 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 spectral width.

High-power (>100mW) 820 nm-band distributed Bragg reflector (DBR) laser diodes (LDs) with stable fundamental transverse mode operation and continuous wavelength tuning characteristics have been developed. To obtain high-power LDs with a stable fundamental transverse mode in 820 nm wavelength range, an AlGaAs narrow stripe (2.0 micrometers ) real refractive-index-guided self-aligned (RISA) structure is utilized. In the RISA structure, the index step between inside and outside the stripe region ((Delta) n) can be precisely controlled in the order of 10 -3 ). To maintain a stable fundamental transverse mode up to an output power over 100 mW, (Delta) n is designed to be 4x10 -3 . Higher-order transverse modes are effectively suppressed by a narrow stripe geometry. Further, to achieve continuous wavelength tuning capability, the three-section LD structure, which consists of the active (700micrometers ), phase control (300micrometers ), and DBR(500micrometers ) sections, is incorporated. Our DBR LDs show a maximum output power over 200mW with a stable fundamental transverse mode, and wavelength tuning characteristics ((Delta) (lambda) ~2nm) under 100 mW CW operation.

The longitudinal mode behavior of AlGaAs lasers with n‐type cladding layers doped with Se and Si is reported. The longitudinal mode of the lasers with highly Se‐doped cladding layer is stabilized, and large hysteresis of mode jump is observed as temperature changes. In the case of highly Si‐doped cladding layers, however, the mode hops to the adjacent one and no hysteresis is observed. These phenomena are explained by the difference in thermal activation energy between Se‐ and Si‐related DX centers.

High-power (greater than 50 mW) and high-temperature (greater than 70 degrees Celsius) operation of 650 nm-band AlGaInP lasers are required as light sources for high-density and recordable optical disk memory systems. However, there remains the problems such as small band-offset in the conduction band and facet degradation in AlGaInP material system which limit the high-power and high-temperature operation. This paper presents new techniques in order to achieve such high performance lasers: Window-mirror structure and real index guided structure.

The InGaN ternary system, which is useful for blue and green light emitting or laser diodes, is studied with respect to an unstable mixing region in the phase field. The unstable region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in GaN and InN is also taken into account in our model. The interaction parameters of InGaN obtained by our analysis for the wurtzite and zinc-blende structures are 7.81 kcal/mol and 6.63 kcal/mol, respectively. According to the calculated results of the interaction parameters, the critical temperature for wurtzite InGaN and zinc-blende InGaN are found to be 1967 K and 1668 K, respectively. This suggests that, at a typical growth temperature of 800°C, a wide unstable mixing region exists in both wurtzite and zinc-blende structures. In order to show the validity of our calculation results, we compare the calculated results and the experimental results using the calculation of the interaction parameter for the InGaAs system. The calculated results agree well with the experimental results.

Low operating current and high temperature operation has been achieved in 650 nm AlGaInP high power double quantum well laser diodes with a real refractive index guided self-aligned (RISA) structure. The attained operating current for 50 mW CW at 70/spl deg/C is as low as 98 mA, which is almost a half of the lowest value ever reported.

Thermodynamic calculations were carried out on chloride transport vapor phase epitaxy of GaN using GaCl3/N2 and NH3/N2. At typical growth temperature and gas flow rates, both GaN formation and gas phase etching reactions of GaN are thermodynamically favored. Under thermodynamic equilibrium, most ammonia should decompose to nitrogen and hydrogen gases and gas phase etching of GaN occurs by HCl. From experimental measurements, less than 10% of the incoming ammonia decomposes and under this condition, GaN formation from GaCl3/N2 and NH3/N2 is thermodynamically favored. Higher V/III ratios give a larger driving force for GaN fromation. These calculations match our experimental results. Experimentally, we have optimized the growth conditions of GaN. High crystalline quality thick GaN films (10 ~ l5µm) were grown on c-Al2O3. The GaN films show band edge emission dominated PL at both room temperature and 77 K. Only one set of diffraction peaks from % MathType!MTEF!2!1!+- % feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB % PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr0x % c9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8fr % Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaadaqada % qaaiaaigdacaaIWaGabGymayaaraGaaGOmaaGaayjkaiaawMcaaaaa % !3C38! $$\left( {10\bar 12} \right)$$ planes with 60° spacing in the ϕ-scan of X-ray diffraction are observed. This indicates that the GaN films grown on c-Al2O3 are single crystalline. Typical growth rates were about 10 ~ l5µm/hr and typical Hall mobility values of GaN films were in the range of 3 to 40 cm2/Vsec.