Strain-compensated InGa(As)P-InAsP active regions for 1.3-μmwavelength lasers

The demonstration of an optimized strain compensated multiple-quantum-well (MQW) active region for use in 1.3-μm wavelength lasers is described. Utilizing narrow bandgap tensile-strained InGaAsP instead of wide bandgap InGaP barriers in strain-compensated lasers, we observe a reduction in threshold current density (Jth) from 675 to 310 A/cm² and in T₀ from 75 K to 65 K for 2-mm long seven quantum-well devices. Additionally, the lowest reported Jth for MBE grown 1.3-μm wavelength lasers of 120 A/cm² for single-quantum-well (SQW) 45-mm-long lasers was attained     

Barrier composition dependence of differential gain and externaldifferential quantum efficiency in 1.3-μm strained-layermultiquantum-well lasers

Dependence of the differential gain and the external differential quantum efficiency on the composition of InGaAsP barrier layers were investigated for 1.3 μm InGaAsP-InGaAsP compressively strained layer (SL) multiquantum well (MQW) lasers. In this investigation, we compared between SL-MQW lasers and unstrained MQW lasers having the same well thicknesses and the same emitting wavelength in order to clarify the effect of strain for each barrier composition. As a result It has been found that the barrier composition has large influence on the differential gain and the external differential quantum efficiency in the SL-MQW lasers. Narrower band-gap barrier means little effect of strain on the differential gain due to the electron overflow from a well layer, while wider band-gap barrier means degradation in the differential gain and the external differential quantum efficiency due to the nonuniform injection of hole into a well layer. In this experiment, the barrier composition of 1.05 μm is suitable for 1.3 μm InGaAsP-InGaAsP SL-MQW lasers to realize large differential gain and high external differential quantum efficiency simultaneously     

Dependence of differential quantum efficiency on the confinementstructure in InGaAs/InGaAsP strained-layer multiple quantum-well lasers

An internal efficiency of 91% was obtained with In_0.7Ga _0.3As/InGaAsP strained-layer multiple quantum well (MQW) lasers emitting at a wavelength of 1.5 μm. The dependence of the reciprocal differential quantum efficiency on the length of the laser cavity shows that the absorption loss in the InGaAsP (λ=1.3 μm) confinement layer caused by carrier overflowing into the confinement layer reduces the internal efficiency     

Threshold currents of 1.3-μm bulk, 1.55-μm bulk, and1.55-μm MQW DFB P-substrate partially inverted buried heterostructurelaser diodes

We investigate the threshold currents of 1.3-μm bulk, 1.55-μm bulk, and 1.55-μm multi-quantum-well (MQW) distributed feedback (DFB) P-substrate partially inverted buried heterostructure (BH) laser diodes experimentally and theoretically. In spite of the larger internal loss of the 1.55-μm bulk laser diodes, the threshold current of the 1.55-μm bulk DFB P-substrate partially inverted BH laser diode is almost the same as that of the 1.3-μm bulk DFB P-substrate partially inverted BH laser diode. The experimentally obtained average threshold current of the 1.3-μm bulk DFB P-substrate partially inverted BH laser diodes is 17 mA and that of the 1.55 μm bulk DFB P-substrate partially inverted BH laser diodes is 16 mA. The calculated threshold current of the 1.3-μm bulk DFB laser diode is 15.3 mA and that of the 1.55-μm bulk DFB laser diode is 18.3 mA, which nearly agree with the calculated values, respectively. We have fabricated two types of five-well 1.55-μm InGaAs-InGaAsP MQW DFB P-substrate partially inverted BH laser diodes. One has barriers whose bandgap energy corresponds to 1.3 μm, and the other has barriers of which bandgap energy corresponds to 1.15 μm. The calculated threshold current of the MQW DFB laser diode with the barriers (λ_g =1.3 μm) is 8.5 mA, which nearly agrees with the experimentally obtained value of 10 mA. However, the calculated threshold current of the MQW DFB laser diode with the barriers (λ_g=1.15 μm) is 7.9 mA which greatly disagrees with the experimentally obtained value of 19 mA, which suggests that the valence band discontinuity between the well and the barrier severely prevents the uniform distribution of the injected holes among five wells     

High-temperature operation of InGaAs/InGaAsP compressive-strainedQW lasers with low threshold currents

We investigated the influence of the band gap wavelength of barrier layers and separate confinement heterostructure (SCH) layers λ_SCH on the high-temperature operation of InGaAs/InGaAsP compressive-strained quantum-well (QW) lasers. The optimum λ_SCH was 1.2 μm, at which carriers were sufficiently confined into quantum wells. The QW laser with λ_SCH = 1.2 μm exhibited low threshold currents of 2.3 mA at 20°C and 9.7 mA at 100°C and CW lasing up to 150°C     

High-performance long-wavelength (λ~1.3 μm) InGaAsPNquantum-well lasers

We demonstrate high-performance InGaAsPN quantum well based long-wavelength lasers grown on GaAs substrates, nitrogen containing lasers emitting in the λ=1.2- to 1.3-μm wavelength range were grown by gas source molecular beam epitaxy using a RF plasma nitrogen source. Under pulsed excitation, lasers emitting at λ=1.295 μm exhibited a record low threshold current density (J_TH) of 2. 5 kA/cm². Lasers grown with less nitrogen in the quantum well exhibited significantly lower threshold current densities of J_TH =1.9 kA/cm² at λ=1.27 μm and J_TH=1.27 kA/cm² at λ=1.2 μm. We also report a slope efficiency of 0.4 W/A and an output power of 450 mW under pulsed operation for nitrogen containing lasers emitting at 1.2 μm     

High T0 long-wavelength InGaAsN quantum-well lasersgrown by GSMBE using a solid arsenic source

We demonstrate high performance, λ=1.3- and 1.4-μm wavelength InGaAsN-GaAs-InGaP quantum-well (QW) lasers grown lattice-matched to GaAs substrates by gas source molecular beam epitaxy (GSMBE) using a solid As source. Threshold current densities of 1.15 and 1.85 kA/cm² at λ=1.3 and 1.4 μm, respectively, were obtained for the lasers with a 7-μm ridge width and a 3-mm-long cavity. Internal quantum efficiencies of 82% and 52% were obtained for λ=1.3 and 1.4 μm emission, respectively, indicating that nonradiative processes are significantly reduced in the quantum well at λ=1.3 μm due to reduced N-H complex formation. These Fabry-Perot lasers also show high characteristic temperatures of T₀ =122 K and 100 K at λ=1.3 and 1.4 μm, respectively, as well as a low emission wavelength temperature dependence of (0.39±0.01) nm/°C over a temperature range of from 10°C to 60°C     

1.5 μm λ/4 shifted multiple quantum well distributedfeedback laser diodes

1.5 μm λ/4 shifted multiple quantum well distributed feedback laser diodes have been achieved for the first time. A characteristic temperature value for a threshold current at around room temperature was as high as 88 K. Spectra at 0.9 times the threshold current showed substantial TM mode suppression. The MQW active region consists of four GaInAs wells (75 Å thick) and GaInAsP barriers (λ_g=1.15 μm, 150 Å thick) grown by metalorganic vapour phase epitaxy (MOVPE). 1.3 μm GaInAsP was grown as an optical guide layer     

Low-temperature sensitive, compressively strained InGaAsP active(λ=0.78-0.85 μm) region diode lasers

This letter reports comparative studies between (Al)GaAs versus InGaAsP active region edge-emitting semiconductor lasers for emission wavelength in the IR regime (λ=0.78-0.85 μm). High characteristic temperature T₀(200 K) and T₁ (450 K) edge-emitting diode lasers have been demonstrated by using the compressively strained (Δa/a=0,6%) Al-free (InGaAsP) active region with an emission wavelength of 0.85 μm. The high T₀ and T ₁ a result of low active-layer carrier leakage, will be beneficial for high-temperature and high-power operation. Implementation for InGaAsP-active VCSEL's with compressively strained InGaAsP-active layers and conventional DBR's is also discussed     

A comparative study of temperature sensitivity of InGaAsP andAlGaAs MQW lasers using numerical simulations

We used numerical simulation to compare the temperature sensitivity of an InGaAsP MQW laser emitting at 1.55 μm and an AlGaAs MQW laser at 0.82 μm. By artificially changing the InGaAsP laser gradually into a structure similar to the AlGaAs laser, we gained quantitative insight into how each material or structural parameter causes the relatively low T₀ of the InGaAsP MQW laser. Using a typical MQW structure we demonstrated the relative importance of parameters involving Auger recombination, current leakage over the quantum barrier, optical confinement and band offset. We found that if these parameters were made the same as the AlGaAs laser, the T₀ of the InGaAsP laser was even better than that of the AlGaAs laser. Our numerical simulation confirmed that the Auger recombination is the main cause of low T₀ in MQW InGaAsP lasers. We also discovered that thermal current leakage over the barrier and Auger recombinations are correlated with each other and both factors must be improved to increase the T₀ of InGaAsP lasers to that of AlGaAs lasers     

Experimental analysis of temperature dependence of oscillationwavelength in quantum-well FP semiconductor lasers

We experimentally evaluated the temperature dependence of the oscillation wavelength in 1.3-μm GaInAsP-InP strained multiple-quantum-well (MQW) semiconductor lasers compared to bulk lasers. The temperature dependence of the oscillation wavelength can be characterized by two newly introduced coefficients α₁ and α₂ which are the gain peak wavelength shift coefficients under the constant current condition and under the constant temperature condition, respectively. These two coefficients of various MQW structure lasers are the same as those of bulk lasers. This result means that the oscillation wavelength shift coefficient dλ/dT is only a function of the characteristic temperature T₀. The higher T₀ induces the large temperature dependence of the oscillation wavelength, When the characteristic temperature T₀ is equal to the characteristic temperature T_ltr of the transparency current I_tr, the oscillation wavelength shift coefficient dλ/dT takes the maximum value which is determined by the thermally induced bandgap narrowing effect dλ _g/dT. One possibility to solve the paradox between a high characteristic temperature T₀ and the small temperature dependence of the oscillation wavelength is the introduction of the temperature-independent leakage current     

Strained 1.3 μm MQW AlGaInAs lasers grown by digital alloy MBE

AlGaInAs strained MQW lasers, emitting at 1.3 μm, have been prepared for the first time using a digital alloy approach. 2 μm stripe geometry lasers have characteristics comparable to those of lasers prepared using bulk alloy layers. The infinite length threshold current densities are as low as 140 kA/cm²/quantum well and T ₀ values (20-40°C) range from 75-90 K for chip lengths of 375-2375 μm     

Tensile-strained GaInAsP-InP quantum-well lasers emitting at 1.3μm

Tensile-strained GaInAsP-InP quantum-well (QW) lasers emitting at 1.3 μm are investigated. Low-pressure metalorganic chemical vapor deposition (LP-MOCVD) is used for crystal growth. High-resolution X-ray diffraction shows good agreement with theoretical simulation, photoluminescence spectra have good energy separation between light-hole and heavy-hole bands due to biaxial tension. The lowest threshold current density for infinite cavity length J_th/N_w ^∞ of 100 A/cm² is obtained for the device with -1.15% strain and N_w=3. The amount of strain which gives the lowest J_th/N_w^∞ experimentally clarified is around -1.2%. Threshold current of a buried-heterostructure (BH) laser is reduced to be as low as 1.0 mA. Enhanced differential gain of 7.1×10^-16 cm² is also confirmed by measurements of relative intensity noise. Much improved threshold characteristic with the feasibility of submilliamp threshold current can be achievable by optimizing the BH structure. The tensile-strained QW laser emitting at 1.3 μm with very low power consumption is attractive for the light source of fiber in the loop system and optical interconnection applications     

High-power operation of aluminum-free (κ=0.98 μm) pumplaser for erbium-doped fiber amplifier

The authors discuss the fabrication and characteristics of high-power (P_CW=430 mW) InGaAs/InGaAsP/InGaP ridge waveguide lasers emitting at λ=0.98 μm, which is the optimum wavelength for pumping erbium-doped fiber amplifiers. In the past, high-power operation of Al-free pump lasers has been limited to 150 mW because of catastrophic optical damage of the mirror facet. This problem has been largely removed by increasing the spot size of the laser with the aid of an improved waveguide design. As a result, Al-free lasers can now achieve a maximum power comparable to the conventional GaAlAs-based pump lasers for λ=0.98 μm     

GaxIn1-xAsyP1-y-InPtensile-strained quantum wells for 1.3-μm low-threshold lasers

Ga_xIn_1-xAs_yP_1-y-InP tensile-strained multiple quantum wells (MQWs) grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) are studied for the application to 1.3-μm lasers. High-resolution X-ray diffraction curves show good agreement with theoretical simulation. Clear energy separation of light hole and heavy hole bands is observed in the room temperature photoluminescence measurement. Threshold characteristics of -1.15% tensile-strained MQW lasers with graded index separate confinement heterostructure (GRINSCH) are investigated. The minimum threshold current density per well (J_th/N_w) for infinite cavity length obtained is 100 A/cm² for the device with a well number of 3. Tensile strain dependence of J_th/N _w for an infinite cavity is also clarified     

InGaAsPN-InP-based photodetectors for long wavelength(λ>1.65 μm) applications

We demonstrate InGaAsPN p-i-n photodetectors lattice-matched to InP substrates with cutoff wavelengths larger than 1.65 μm. The narrow bandgap InGaAsPN absorption layers were grown by gas source molecular beam epitaxy using an RF plasma nitrogen source. Optical absorption spectra reveal that InGaAsPN with 5% P and 2.8% N has a cutoff wavelength λ_CO=1.90 μm Background doping in the absorption layer for a detector with 1.5% N and 5% P is reduced from (1.5±0.5)×10¹⁷ cm^-3 for the as-grown device, to (5±0.5)×10¹⁶ cm^-3 for a thermally annealed device. The unintentional high background doping is due to N-H bond formation or local strain induced defects. Spectral response measurements indicate that λ_CO=1.85 μm is achieved for detectors annealed at 800°C with 2% N and 5% P in the InGaAsPN absorption layer, suggesting that annealed InGaAsPN alloys are promising for use in detectors with response in the near and mid-IR wavelength spectral range     

Enhanced relaxation oscillation frequency and reduced nonlinear K-factor in InGaAs/InGaAsP MQW lambda /4-shifted DFB lasers

The relaxation oscillation frequency, f/sub r/, of 1.55 mu m InGaAs/InGaAsP MQW lambda /4-shifted DFB lasers was doubled by increasing the carrier injection efficiency into each quantum well, which results from an optimised bandgap energy and optimised thickness of the barrier layers. The nonlinear K-factor which determines the maximum modulation bandwidth through the damping phenomenon can be reduced by adopting a p-type modulation doped MQW structure in the active layer.<>     

Low-threshold current, high-efficiency 1.3-μm wavelengthaluminum-free InGaAsN-based quantum-well lasers

We demonstrate high-performance Al-free InGaAsN-GaAs-InGaP-based long-wavelength quantum-well (QW) lasers grown on GaAs substrates by gas-source molecular beam epitaxy using a RF plasma nitrogen source. Continuous wave (CW) operation of InGaAsN-GaAs QW lasers is demonstrated at λ=1.3 μm at a threshold current density of only J_TH =1.32 kA/cm². These narrow ridge (W=8.5 μm) lasers also exhibit an internal loss of only 3.1 cm^-1 and an internal efficiency of 60%. Also, a characteristic temperature of T₀=150 K from 10°C to 60°C was measured, representing a significant improvement over conventional λ=1.3 μm InGaAsP-InP lasers. Under pulsed operation, a record high maximum operating temperature of 125°C and output powers greater than 300 mW (pulsed) and 120 mW (CW) were also achieved     

Influence of free carrier plasma effect on carrier-inducedrefractive index change for quantum-well lasers

The influence of the free carrier component due to the plasma effect on carrier-induced refractive index change and its dependency on polarization for multiple-quantum-well (MQW) and bulk lasers are experimentally studied. The ratios of the component to the total index change, R_fc, are 0.6, 0.4, and 0.1 for 1.3-μm MQW, 1.3-μm bulk, and 0.8-μm MQW lasers, respectively. The TM/TE polarization ratios of the component, R_TMTE/, are 0.8 and 0.3 for 1.3-μm MQW and 0.8-μm MQW lasers. The relationship between the index change and the carrier overflow (to barrier and separate confinement heterostructure layers) for MQW lasers is also discussed. Large R_fc and R_TMTE/ for the 1.3-μm MQW laser result from the carrier overflow     

High-performance λ=1.3 μm InGaAsP-InP strained-layerquantum well lasers

Compressively and tensile strained InGaAsP-InP MQW Fabry-Perot and distributed feedback lasers emitting at 1.3-μm wavelength are reported. For both signs of the strain, improved device performance over bulk InGaAsP and lattice-matched InGaAsP-InP MQW lasers was observed. Tensile strained MQW lasers show TM polarized emission, and with one facet high reflectivity (HR) coated the threshold currents are 6.4 and 12 mA at 20 and 60°C, respectively. At 100°C, over 20-mW output power is obtained from 250-μm-cavity length lasers, and HR-coated lasers show minimum thresholds as low as 6.8 mA. Compressively strained InGaAsP-InP MQW lasers show improved differential efficiencies, CW threshold currents as low as 1.3 and 2.5 mA for HR-coated single- and multiple quantum well active layers, respectively, and record CW output powers as high as 380 mW for HR-AR coated devices. For both signs of the strain, strain-compensation applied by oppositely strained barrier and separate confinement layers, results in higher intensity, narrower-linewidth photoluminescence emissions, and reduced threshold currents. Furthermore, the strain compensation is shown to be effective for improving the reliability of strained MQW structures with the quantum wells grown near the critical thickness. Linewidth enhancement factors as low as 2 at the lasing wavelength were measured for both types of strain. Distributed feedback lasers employing either compressively or tensile strained InGaAsP-InP MQW active layers both emit single-mode output powers of over 80 mW and show narrow linewidths of 500 kHz