Device characteristics of GaAlAs buried-multiquantum-well lasers fabricated by Zn-diffusion-induced disordering

A new transverse mode controlled buried-multiquantum-well (BMQW) laser has been fabricated using the simple and reliable Zn-diffusion-induced disordering process. BMQW lasers are characterized by low threshold current (20 mA) and single transverse and longitudinal mode oscillation. It is observed that the threshold current is proportional to the stripe width and the transverse mode is controlled by controlling the stripe width. From these results, it is confirmed that the BMQW structure provides good optical confinement as well as current confinement.     

Controlled Zn diffusion for low threshold narrow stripe GaAlAs/GaAs DH lasers

Zn diffusion was accurately controlled to reach within the active region of a GaAlAs/GaAs DH laser. The diffused 4 µm stripe lasers have threshold currents as low as 40 mA and exhibit single longitudinal mode oscillation in a wide range of current levels.     

Oscillation characteristics in InGaAsP/InP DH lasers with self-aligned structure

This paper presents new stripe geometry InGaAsP/InP DH lasers having mechanisms for suppressing current spreads and for controlling the transverse mode parallel to the junction plane. The theoretical study for optimum design of these lasers from which the analytic method of oscillation characteristics, including control of the transverse mode parallel to the junction plane attributable to refractive index and gain, was derived is discussed. The oscillation characteristics, especially the waveguide properties of the transverse mode are reported. Experimental results show excellent agreement with the theory and show that the transverse mode is totally confined by the built-in passive waveguide for a stripe width of 5 μm.     

质量迁移层对InGaAsP BH半导体激光器阈值电流和模式行为的影响

用 Schwarz-Christoffel变换法计算了质量迁移InGaAsP BH激光器中的结电压分布;分析了迁移层和有源层侧向厚度,上限制层空穴浓度和有源层注入电流对迁移层同质结漏电流的影响;并提出以过渡模式为界,区分A类和B类模式,从理论上比较全面地分析了五层对称平板波导的模式行为;指出降低阈值电流和保证单基横模工作这两方面对迁移层厚度有相反的要求,从而存在一定意义下的最佳迁移层厚度.     

Continuous microwave oscillations in GaAs junction lasers

Microwave oscillations produced by continuously operating GaAs stripe geometry junction lasers are reported here for the first time. These oscillations have been measured both in the light output of the diodes and in the dc current applied to the laser connections. The frequency of the oscillation lies in the 0.5- to 3.0-GHz range and depends strongly on current and temperature. The frequency typically increases with increasing current at a rate of 15 to 20 MHz/mA and decreases with increasing temperature at 100 to 150 MHz/°K. Introduction of an external microwave signal locks the frequency of the oscillation and reduces the oscillation width from 10 MHz to the external signal width. The frequency of oscillation agrees with a theory of intensity fluctuations in lasers based on the rate equations.     

Current thresholds in stripe-contact injection lasers

A mathematical analysis has been made of the current distribution beyond the edge of the contact in a stripe contact injection laser structure. An analytical solution is obtained for this distribution using a simplified but reasonably accurate model. For a typical stripe-contact laser, the junction current beyond the contact region is equivalent to the current at threshold through an additional stripe width of the order of 10 μm. As a result of such current spreading, lasers with narrow stripe-contacts will have greatly increased apparent threshold current densities.     

Near-field emission of lead-sulfide-selenide homojunction lasers

Measurements of the near-field intensity distributions of three lead-sulfide-selenide diode lasers operating near 4.8 μm have been made as a function of injection current. Localized emission in the near field exhibits peaked structure of full width from 5 to 10 μm for operation above threshold. From the dependence of the emission profiles on injection current estimates of 25 cm^-1and 0.09 cm/A are made for the distributed loss and gain coefficients for one of the lasers. Optical confinement perpendicular to the p-n junction can be explained in terms of the homojunction properties.     

Observations of self-focusing in stripe geometry semiconductor lasers and the development of a comprehensive model of their operation

Experimental measurements of the optical-beam parameters of conventional oxide-insulated GaAs stripe-geometry lasers as a function of stripe width have shown a marked difference in the waveguide mechanism of narrow-stripe (simeq10 mum) and wide-stripe (>20 mum) lasers. The optical wave of narrow-stripe lasers is guided by the previously reported gain-guiding mechanism. The optical wave of wide-stripe lasers is found to be guided by changes in the real part of the dielectric constant that are caused by a dip in carrier concentration along the axis of the lasing filament. This self-focused guiding has been predicted theoretically. These experimental results strongly support the hypothesis that in all cases the waveguides are formed predominantly by the naturally occurring variations in carrier concentration beneath the stripe. A new and fairly comprehensive mathematical model has been developed based on this assumption. The model predicts the carrier concentration, resultant gain, and dielectric constant profiles together with the optical-beam parameters and light/current characteristics of stripe-geometry lasers. The model is applicable over a wide range of stripe widths and device structures. The results are compared with experiment over the range of stripe widths from10-20 mum and found in reasonable agreement. The effects of narrowing the stripe width below 10 μm are calculated and found to be in qualitative agreement with recently published experimental results. In particular the light-output power at which a predicted "kink" in the light/current characteristic occurs is found to increase rapidly as the stripe width reduces.     

Theoretical and experimental study of threshold characteristics in InGaAsP/InP DH lasers

Threshold characteristics of stripe-geometry InGaAsP/InP double-heterostructure injection lasers have been analytically derived as a function of active layer thickness and stripe width. The effects of stripe width, refractive index in the active layer, diffusion of injected carriers, carrier lifetime, absorption loss in the cladding layer, gain coefficient, and cavity length on the optimum thickness of the active layer which gives minimum threshold or on threshold current density were studied. These lasers were fabricated on     

Gain and carrier lifetime measurements in AlGaAs multiquantum well lasers

We have measured the gain and the carrier lifetime at threshold in shallow proton stripe AlGaAs multiquantum well lasers with several different active layer structures. The lasers studied had active layers with two wells, four wells, six wells, and the modified multiquantum well. The net gainGis found to vary almost linearly with the injection currentIfor all the laser structures studied. The slopedG/dIis largest for the modified multiquantum well (MMQW) laser which is consistent with the observed lowest threshold current of these devices. We find that the carrier density at threshold for the MMQW laser is about a factor of 4 lower than that for a single quantum well laser. Thus, the effect of a nonradiative mechanism (e.g., Auger effect) which varies superlinearly with the injected carrier density is considerably reduced in MMQW lasers compared to that in single quantum well (SQW) lasers or the conventional double heterostructure lasers. The reduced threshold carrier density of the MMQW lasers has important implications for high temperature performance of lasers fabricated from the InGaAsP/InP material systems which are believed to have nonradiative mechanisms that vary superlinearly with carrier density, particularly for those laser structures for which the high temperature operation is not limited by leakage current.     

A new d.h. laser configuration with passive transverse field confinement

A new geometry is proposed which significantly improves the characteristics of single mode d.h. stripe geometry lasers, with regard to astigmatism of the near field, transverse field confinement, modal gain and threshold current. The advantages over other devices are discussed. Numerical results are presented for 5 and 10 ?m stripe lasers.     

Properties of diffused PbSnSe homojunction diode lasers

The properties of diffused PbSnSe homojunction diode lasers based on the confinement of injected carriers and of light in the fundamental transverse laser mode are investigated both theoretically and experimentally. The electrostatic potential profile near the graded junction is evaluated for the strongly forward biased case. Resulting injection and gain profiles are narrow and their widths increase with temperature. Free carrier dispersion leads to an optical confinement. From the threshold condition for the TEM00mode, the threshold current density is obtained, assuming a minority carrier lifetime of 2 ns. PbSnSe diode lasers were fabricated by diffusion of cadmium under different conditions. Experimental laser properties for different junction gradings are discussed in terms of the model. Threshold currents and output powers as a function of temperature, as well as maximum operating temperature and mode behavior, are consistent with the theoretical expectations.     

High-temperature operation of InGaAs strained quantum-well lasers

Strained-layer quantum-well (SQW) laser structures have been investigated for avionics applications requiring high-temperature performance. The authors have successfully demonstrated InGaAs-GaAs SQW lasers capable of CW operation up to 200 degrees C with more than 5 mW single-mode optical power. These lasers have an emission wavelength of approximately=980 nm, threshold current density of 200 A/cm/sup 2/, differential quantum efficiency of 60%, high output power of approximately=1 W with 50 mu m stripe, and characteristic temperature of 130-140 K.<>     

Channelled-substrate narrow-stripe GaAs/GaAlAs injection lasers with extremely low threshold currents

Channelled-substrate GaAs/GaAlAs injection lasers with very narrow current-confining stripe contacts are described. They have threshold currents less than half those previously reported for this type of device. The best devices had a room-temperature threshold current of only 12 mA pulsed and 14 mA c.w. The lasers also have very good high-temperature performance and c.w. operation has been obtained up to 160°C.     

Heterostructure injection lasers

A state-of-the-art discussion of heterostructure injection lasers is presented. These lasers are first considered as configurations of uniformly pumped semiconductor slabs that constitute the transmission medium of multilayered slab waveguides, whose boundaries are trapless heterojunctions. Emphasis is on lasers whose electrically active and waveguiding layers are AlxGa1-xAs or GaAs, although several other semiconductors are discussed. Single, double, and separate confinement hetrostructure lasers, all of which yield carrier and optical confinement normal to the plane of the heterojunctions, are described. Lateral electrical and optical confinement in various stripe geometry double-hetrostructure lasers is illustrated. In addition to the more common Fabry-Perot cavity lasers, there are now also several new varieties that use corrugated surfaces as Bragg gratings for internal distributed feedback or reflection. Some of these heterostructure lasers have permitted the demonstration of CW-room temperature injection lasers with low threshold current densities (< 1000 A/cm²), low dc current (∼15 mA), long lives (>10⁵) h), and a considerable degree of control over modes and beam divergence. In addition, the use of heterostructures has permitted the demonstration of the first integratedoptical structures that include both active light generating and passive elements on a single chip.     

Development of self-pulsations due to self-annealing of proton bombarded regions during aging in proton bombarded stripe-geometry AlGaAs DH lasers grown by molecular beam epitaxy

Experimental observations indicate that the occurrence of optical self-pulsation in proton delineated stripe-geometry double-heterostructure junction lasers is related to the degree of gain guiding inherent in individual lasers. We show that an aging process occurs during lasing operation which has the effect of partially annealing the proton induced carrier removal concentration at the edges of the active stripe of the laser. In some lasers, the magnitude of this annealing effect is sufficiently large to flatten the active stripe carrier concentration profile thus reducing filament stability leading ultimately to optical self-pulsation. It is shown that the carrier concentration profile modification is due to the dual effects of decreasing then = 2nonradiative current component at the active stripe-proton bombarded interface as well as the geometric effect of increasing the laser active stripe width. This latter effect may be also responsible for some portion of laser threshold current increase observed during device operation.     

Generalized BV diagrams for higher order transverse modes in planarvertical-cavity laser diodes

We use a new class of complex dispersion characteristics to analyze threshold properties of gain-guided vertical-cavity lasers. The analysis gives a fundamental gain limit for single transverse mode oscillation. The general behavior of higher order transverse modes is described by rather universal diagrams that are useful as a guideline for practical device design. A comparison between gain- and index-guided devices shows differences in effective modal gains and wavelength separations between fundamental and neighboring higher order modes. For near threshold operation of gain-guided lasers, the suppression of higher transverse modes is generally improved for large mirror reflectivities. The discussion of real devices considers the important influence of the current induced parasitic temperature profile     

Room-temperature pulsed operation of triple-quantum-well GaInNAslasers grown on misoriented GaAs substrates by MOCVD

The lasing operation of three-quantum-well GaInNAs stripe geometry lasers grown by MOCVD on 0° and 6° misoriented (100) GaAs substrates, respectively, have been demonstrated and their performance is compared for the first time. Both devices achieved room temperature, pulsed lasing operation at an emission wavelength of 1.17 μm, with a threshold current density of 667 A/cm² for lasers grown on 6° misoriented substrates, and 1 kA/cm² for lasers grown on 0° misoriented substrates. The threshold for the lasers grown on 6° misoriented substrates compares favorably with the best results for GaInNAs lasers. Lasers with narrower stripe width and a planar geometry have also been demonstrated by the use of lateral selective wet oxidation for current confinement, with a threshold current density of 800 A/cm² for 25-μm-wide devices     

Stable transverse mode oscillation in planar stripe laser with deep Zn diffusion

The guiding mechanism in a planar stripe laser with deep Zn diffusion under the lasing conditions was investigated both theoretically and experimentally. The conditions necessary to realize refractive index guiding depend on a combination of electron and hole concentrations. The lasers under refractive index guiding, whose stripe width is less than twice the diffusion length, with an adequate combination of electron and hole concentrations, show stable fundamental transverse mode oscillation up to three times the threshold current level.     

High-quality 1.3 ?m GaInAsP/InP BH-DFB lasers with first-order gratings

High-quality 1.3 ?m GaInAsP/InP BH-DFB lasers have been demonstrated. The threshold current was 16 mA and the differential quantum efficiency was 25% per facet. A stable single-longitudinal-mode oscillation was obtained, both up to four times the threshold current and up to 85°C. These results are comparable or superior to reported results of Fabry-Perot BH lasers.