Gain measurements in 1.3 µm InGaAsP-InP double heterostructure lasers

The net gain per unit length (G) versus current (I) is measured at various temperatures for 1.3 μm InGaAsP-InP double heterostructure lasers.Gis found to vary linearly with the currentIat a given temperature. The gain bandwidth is found to decrease with decreasing temperature. The lasing photon energy decreases at 0.325 meV/K with increasing temperature. Also, the slopedG/dIat the lasing photon energies decreases with increasing temperature. This decrease is more rapid forT > sim210K. This faster decrease is consistent with the observed higher temperature dependence of threshold (low T0at high temperatures) of 1.3 μm InGaAsP lasers. A carrier loss mechanism, due to Auger recombination, also predicts thatdG/dIshould decrease much faster with increasing temperature at high temperatures. We also find that the slopedG/dIdecreases slowly with increasing temperature for a GaAs laser, which is consistent with the observed temperature dependence of threshold of these lasers.     

Temperature dependence of lasing characteristics forlong-wavelength (1.3-μm) GaAs-based quantum-dot lasers

Data are presented on the temperature dependence of 1.3-μm wavelength quantum-dot (QD) lasers. A low-threshold current density of 90 A/cm² is achieved at room temperature using high reflectivity coatings. Despite the low-threshold current density, lasing at the higher temperatures is limited by nonradiative recombination with a rapid increase in threshold current occurring above ~225 K. Our results suggest that very low threshold current density (⩽20 A/cm ²) can be achieved at room temperature from 1.3-μm QD lasers, once nonradiative recombination is eliminated     

Comparison of the electrical characteristics and threshold temperature dependences of λ ~ 1.3 µm and λ ~ 1.6 µm stripe-geometry InGaAsP DH lasers

Light-current and derivative voltage-current characteristics are compared for dielectric-isolated stripe-geometry InGaAsP DH lasers operating under both pulsed and continuous excitation at wavelengths near 1.3 and 1.6 μm. At both wavelengths the lasers have comparable threshold temperature dependences, and both exhibit similar kinks and light jumps in their characteristics. The low T0values observed (sim50- 70K) cannot be attributed to drift-current losses.     

High-efficiency stripe-geometry InGaAsP DH lasers (λ = 1.3 µm) with chemically-etched mirrors

Stripe-geometry InGaAsP double heterojunction lasers with chemically-etched mirrors have been fabricated. External differential quantum efficiencies as high as ∼ 30% have been obtained for devices with two chemically-etched mirrors. Etched-mirror lasers with 25 µm wide stripes have threshold currents as low as 210mA (room-temperature, pulsed). The etched-mirror lasers are compared to cleaved-mirror devices prepared from the same wafer.     

Criterion for improved linearity of 1.3-µm InGaAsP-InP buried-heterostructure lasers

Nonlinearities in tile light-current characteristics of planar-active buried-heterostructure (BH) lasers are associated with higher order mode transitions, spectral broadening and, in some cases, the onset of TM polarized stimulated emission. Measurements and calculations are presented which show that these nonlinearities appear at higher power in devices with reduced active volume. These results provide a practical guide to the fabrication of "kink-free" 1.3-μm InGaAsP buried-heterostructure lasers for use in high-bit-rate fiber communication systems.     

Fabrication and lasing properties of mesa substrate buried heterostructure GaInAsP/InP lasers at 1.3 µm wavelength

Fabrication and lasing properties of novel GaInAsP/InP injection lasers at 1.3 μm, with buried heterostructure grown on mesa substrate and fabricated by single-step crystal growth are reported. In this mesa substrate buried heterostructure (MSB) laser, the GaInAsP active layer was grown separately on the top of a mesa structure formed along the surface of a     

Reliability in InGaAsP/InP buried heterostructure 1.3 µm lasers

A study was conducted of aging-induced Sn whisker growth at the surface of Au-Sn bonding solder layers around a laser chip, as well as metallurgical reactions, especially in p-side down lasers, at the interface of the solder and laser crystal just below the active layer. These phenomena cause electrical shorts in InGaAsP/InP laser diodes, which occur suddenly in devices operated for long periods without any previous symptoms having appeared in their aging characteristics. To completely eliminate such failures, a novel assembling method in which chips were mounted p-side up on semiinsulating SiC submounts using Pb-Sn solder, was applied to InGaAsP/InP buried heterostructure (BH) lasers emitting at 1.3 μm. BH lasers assembled by this method do not suffer any shorting failure even after 8000 h operation under 60°C and 5 mW/facet output conditions. The small degradation rates obtained, for example, 3 percent/kh (median) at 60°C, certify the reliability of these improved lasers. As long as the stripe width of the active layer was optimized to be in the range of1.5-2.5 mum necessary for obtaining kink-free light output versus current properties, no detrimental changes in laser characteristics, including transverse and longitudinal modes and dynamic output response, were observed in aged lasers. In this paper, the long-term degradation modes observed are presented, and possible causes are discussed.     

Low-threshold InGaAsP ridge waveguide lasers at 1.3 µm

The ridge waveguide configuration is shown to provide reliable low-threshold fundamental-transverse-mode lasers that are readily fabricated. Two variants are described: in the simple ridge laser, the 1.3 μm bandgap active layer is sandwiched between InP layers and in the cladded ridge, the active layer is surrounded by 1.1 μm bandgap InGa AsP. Thresholds as low as 34 mA and efficiencies as high as 66 percent are observed. Output power is linear to more than 12 mW. Several lasers have been operated at 30°C for over 1500 h without measurable degradation. Selected lasers exhibit stabilized longitudinal mode behavior over extended temperature and current ranges. The potential manufacturability of this device is its most attractive feature.     

Temperature characteristics of double-carrier-confinement (DCC) heterojunction InGaAsP(λ = 1.3 µm)/InP lasers

This paper reports on a detailed study of the oscillation characteristics of double-carrier-confinement (DCC) heterojunction InGaAsP(lambda = 1.3 mum)/InP lasers, with special emphasis on their temperature characteristics. In addition to conventional double-heterojunction lasers, these lasers have a p-InGaAsP second active layer sandwiched between the p-InP clad layers. The spectral characteristics below threshold were examined in order to verify electron leakage beyond the hetero-barrier of the p-InP thin clad layer, and to study the contribution of the second active layer to optical gain and laser action. Threshold temperature characteristics were also investigated through an analysis of the heterojunction energy band structure. The results indicate that emission from the second active layer is caused by electron leakage. In order to obtain high temperature stability for these lasers, it is essential that both the first and second active layers contribute to the optical gain spectrum and laser action.     

Amplifying medium characteristics in optimized 190 µm/195 µm DCN waveguide lasers

Extensive study of the CW, dischaxge-pumped, DCN laser operating on the (22⁰0-09¹0) 190 and 195 μm lines has been undertaken in order to develop a new source of radiation suitable for plasma diagnostics. The optimum values of the parameters of the discharge, the unsaturated gain, and the saturation intensity are given as a function of the tube diameter. Scaling laws predicting the maximum output power as a function of the tube dimensions and of the cavity loss are established. Such lasers compare favorably with optically pumped submillimeter lasers, since 250 mW are available from a 3 m long, 5 cm diameter waveguide DCN laser.     

Band-to-band Auger processes in 1.3 µm InGaAsP semiconductor lasers

Within the context of the four-band Kane model, we have analyzed the contributions of pure collision and phonon-assisted CHSH and CHCC Auger processes to the nonradiative recombination lifetime in highly excited InGaAsP. Our method incorporates refined expressions for the wavefunction overlap integrals and spectral density functions, and avoids approximations to Fermi and phase-space factors. Our results are in good agreement with recent experiments, despite a rather large uncertainty associated with the unavailability of precise values for certain band-structure parameters.     

Temperature dependence of Al/undoped Al0.5Ga0.5As/GaAs capacitors

Undoped Al0.5Ga0.5As is used in place of the insulator layer in the fabrication of MIS-type capacitors with Schottky gates. The current-voltage and capacitance-voltage characteristics of the capacitors were measured as a function of temperature in the range 300-77 K. At high temperatures current is by thermionic emission over the barrier determined by the Schottky contact and the Al0.5Ga0.5As/ GaAs conduction band discontinuity. As the temperature is lowered, Fowler-Nordheim tunneling is observed at sufficiently large gate biases and at 77 K conduction is ohmic. Based on I-V and C-V data the electron accumulation layer density is estimated to be about 1 × 10¹²cm^-2at 77 K when the capacitor is positively biased. The results obtained indicate that for an appropriate choice of parameters it should be possible to fabricate MIS-like transistors suitable for high-speed operation at 77 K.     

Ultra-High speed InGaAsP/InP DFB lasers emitting at 1.3 µm wavelength

A bandwidth of 13 GHz has been attained in a 1.3 μm DFB laser at 25 °C. A mesa structure was introduced to reduce the parasitic capacitance and the lasing wavelength was detuned from the gain peak to increase the differential gain. This bandwidth is the widest so far reported in 1.3 μm DFB lasers.     

Frequency response of 1.3µm InGaAsP high speed semiconductor lasers

The frequency response of a group of 1.3 μm InGaAsP vapor-phase-regrown buried heterostructure lasers of various cavity lengths is analyzed by fitting the measured response curves. The dependence of resonant frequency f0and damping rateGammaon bias power is determined. The differential gain coefficient for InGaAsP is determined as3.5 times 10^{-16}cm². The damping rate is found to be proportional to the square of the resonant frequency with a proportionality factor which is independent of device geometry and facet reflectivity. The existence of such a universal relationship betweenGammaand f0and the observed magnitude of the damping rate is explained by the interband relaxation model of nonlinear gain.     

Efficient 1.06-µm emission from InxGa1-xAs electroluminescent diodes

Vapor-grown p-n junctions of InxGa1-xAs have been prepared that emit near-bandgap infrared radiation at 1.06 µm with an external quantum efficiency in excess of 1 percent at room temperature. These diodes have an electroluminescence response time of 20 ns. In addition, InxGa1-xAs injection lasers have been fabricated with threshold current densities between 2000 and 3000 A/cm²at 80 K. The importance of internal absorption losses in determining the spectral distribution and the electroluminescence efficiency at room temperature is described.     

Growth and characterization of 1.3 µm CW GaInAsP/InP lasers by liquid-phase epitaxy

The variation of the threshold current density and its temperature dependence with acceptor concentration in GaInAsP/InP lasers emitting at 1.3 μm is described. Mechanisms responsible for the dependence are identified. A model is developed to predict the effect of the above dependence on the CW operation range of these devices. The validity of the model is verified experimentally.     

High-power output over 200 mW of 1.3 µm GaInAsP VIPS lasers

Maximum CW output power was investigated in GaInAsP 1.3μm V-grooved inner stripe on P-substrate (VIPS) lasers considering both cavity length and facet reflectivity. Long-cavity lasers show a strong dependence of maximum output power on front reflectivity. A CW light output over 200 mW was obtained at room temperature using a 700 μm long cavity laser with 5 and 98 percent reflectivity of the front and rear facets, respectively. The fundamental transverse mode operation was confirmed up to 170 mW. A coupled power over 110 mW into a single-mode fiber was achieved with a coupling efficiency of 58 percent. We have verified the high reliability under high power levels, as high as 75 percent of the maximum CW output powers at room temperature.