K. Kumada

High-performance CW 1.26-/spl mu/m GaInNAsSb-SQW ridge lasers

Long wavelength GaInNAsSb-SQW lasers and GaInAsSb-SQW lasers that include a small amount of Sb were successfully grown by gas-source molecular beam epitaxy (GSMBE). We confirmed that Sb reacts in a highly strained GaInAs-GaAs system and GaInNAs-GaAs system like a surfactant, which increases the critical thickness at which the growth mode changes from two-dimensional (2-D) growth to three-dimensional (3-D) growth. The lasers were processed into ridge lasers. The GaInNAsSb lasers oscillated under continuous-wave (CW) operation at 1.258 /spl mu/m at room temperature. The low CW threshold current of 12.4 mA and high characteristic temperature (T/sub c/) of 157 K were obtained for GaInNAsSb lasers, which is the best result for GaInNAs-based narrow stripe lasers. Further, the GaInNAsSb laser oscillated under CW conditions over 100/spl deg/C. On the other hand, GaInAsSb lasers oscillated under CW operation at 1.20 /spl mu/m at room temperature. The low CW threshold current of 6.3 mA and high characteristic temperature (T/sub c/) of 256 K were obtained for GaInAsSb lasers, which is also the best result for 1.2-/spl mu/m-range highly strained GaInAs-based narrow stripe lasers. We can say that GaInNAsSb lasers are very promising material for realizing an access network. Further, the differential gain of GaInNAs-based SQW lasers was estimated for the first time. GaInNAsSb-SQW lasers have the extremely large differential gain of 1.06-10/sup -15/ cm/sup 2/ in spite of the single-QW lasers; therefore, GaInNAsSb lasers are also suitable for high-speed lasers in the long wavelength region.

1.3-/spl mu/m-range GaInNAsSb-GaAs VCSELs

1.3-/spl mu/m-range GaInNAsSb vertical-cavity surface-emitting lasers (VCSELs) with the doped mirror were investigated. GaInNASb active layers that include a small amount of Sb can be easily grown in a two-dimensional manner as compared with GaInNAs due to the suppression of the formation of three-dimensional growth in MBE growth. The authors obtained the lowest J/sub th/ per well (150 A/cm/sup 2//well) for the edge-emission type lasers due to the high quality of GaInNAsSb quantum wells. Using this material for the active media, the authors accomplished the first continuous wave operation of 1.3-/spl mu/m-range GaInNAsSb VCSELs. For the reduction of the threshold voltage and the differential resistance, they used the doped mirror grown by metal-organic chemical vapor deposition (MOCVD). By three-step growth, they obtained 1.3-/spl mu/m GaInNAs-based VCSELs with the low threshold current density (3.6 kA/cm/sup 2/), the low threshold voltage (1.2 V), and the low differential resistance (60 /spl Omega/) simultaneously for the first time. The back-to-back transmission was carried out up to 5 Gb/s. Further, the uniform operation of 10-ch VCSEL array was demonstrated. The maximum output power of 1 mW was obtained at 20/spl deg/C by changing the reflectivity of the front distributed Bragg reflector mirror. GaInNAsSb VCSELs were demonstrated to be very promising material for realizing the 1.3-/spl mu/m signal light sources, and the usage of the doped mirror grown by MOCVD is the best way for 1.3-/spl mu/m VCSELs.

High-performance 1.3-/spl mu/m InAsP strained-layer quantum-well ACIS (Al-oxide confined inner stripe) lasers

We have demonstrated high-performance 1.3-/spl mu/m InAsP strained-layer quantum-well lasers with Al-oxide confined inner stripe (ACIS) structure. The oxidized layers are consisted of strain-compensated AlAs-InP-AlInAs (6 nm/2 ML/3 nm) superlattice (SAS) layers and grown on InP substrate using gas-source molecular beam epitaxy (GS-MBE). For the structural optimization of the ACIS laser, the dependence of quantum efficiency, threshold current and lateral mode characteristics on the initial ridge width and the current aperture width have been investigated. A very low-threshold current of 2.0 mA, a high differential quantum efficiency of 67% and stable single lateral mode operation of over 40 mW were obtained for the optimized ACIS lasers. The excellent characteristics obtained in the ACIS lasers are attributed to both the current and the optical confinements by the Al-oxide layer. In addition, we confirmed high uniformity of the threshold current and the oxidized width. This device is very promising candidate for low-cost access networks and optical interconnects.

1.3-/spl mu/m InAsP n-type modulation-doped MQW lasers grown by gas-source molecular beam epitaxy

The effect of n-type modulation doping as well as growth temperature on the threshold current density of 1.3-/spl mu/m InAsP strained multiple-quantum-well (MQW) lasers grown by gas-source molecular beam epitaxy (GSMBE) was investigated for the first time. We have obtained threshold current density as low as 250 A/cm/sup 2/ for 1200-/spl mu/m long devices. The threshold current density per well for infinite cavity length J/sub th//N/sub w/spl infin// of 57 A/cm/sup 2/ was obtained for the optimum n-doping density (N/sub D/=1/spl times/10/sup 18/ cm/sup -3/) and the optimum growth temperature (515/spl deg/C for InP and 455/spl deg/C for the SCH-MQW region), which is about 30% reduction as compared with that of undoped MQW lasers. A very low continuous-wave threshold current of 0.9 mA have been obtained at room temperature, which is the lowest ever reported for long-wavelength lasers using n-type modulation doping, and the lowest results grown by all kinds of MBE in the long-wavelength region. The differential gain was estimated by the measurement of relative intensity noise. No significant reduction of differential gain was observed for n-type MD-MQW lasers as compared with undoped MQW lasers. The carrier lifetime was also reduced by about 33% by using n-type MD-MQW lasers. Both reduction of the threshold current and the carrier lifetime lead to the reduction of the turn-on delay time by about 30%. The 1.3-/spl mu/m InAsP strained MQW lasers using n-type modulation doping with very low power consumption and small turn-on delay is very attractive for laser array application in high-density parallel optical interconnection systems.

Low-threshold GaInNAsSb quantum well lasers

Long wavelength-GaInNAsSb quantum well lasers that include small amount of Sb were successfully grown by gas-source molecular beam epitaxy (GSMBE). We confirmed that Sb reacts in GaInNAs/GaAs system like a surfactant, which increase the critical thickness at which the growth mode changes from the 2-dimensional (2-D) growth to the 3-dimensional (3-D) growth. The GaInNAsSb/GaAs lasers oscillated under CW operation at 1.258micrometers at room temperature. The low CW threshold current of 12.4mA and high characteristic temperature (T()) of 157K were obtained for GaInNAsSb/GaAs lasers, which is the best result for GaInNAs- based narrow stripe lasers. To extend the lasing wavelength over 1.3micrometers with keeping the threshold density low, we adopted GaNAs barriers instead of GaAs barriers. We obtained the very low threshold current density of 570A/cm2 at 900micrometers -long cavity with the lasing wavelength of 1.308micrometers . We can say that GaInNAsSb lasers are very promising material for realizing peltier-free devices for access network.

1.3 /spl mu/m-GaInNAsSb based material and its application to VCSELs

1.3 /spl mu/m-range GaInNAsSb material and its application to VCSELs were investigated. GaInNAsSb active layer that include the small amount of Sb can be easily grown in 2 dimensional manner as compared with GaInNAs due to the suppression of the formation of 3-dimensional growth in MBE growth. We obtained the lowest Jth per well (150A/cm/sup 2//well) as for the edge-emission type lasers due to the high quality of GaInNAsSb-QW. Using this material for the active media, we accomplished the first CW operation of 1.3 /spl mu/m-range GaInNAsSb VCSELs.

1.26 /spl mu/m GaInNAsSb-SQW lasers grown by gas-source MBE

Long wavelength-GaInNAsSb SQW lasers that include a small amount of Sb were successfully grown by gas-source molecular beam epitaxy (GSMBE). We confirmed that Sb reacts in the highly strained GaInNAs/GaAs system like a surfactant, which increase the critical thickness at which the growth mode changes from the 2-dimensional (2-D) growth to the 3-dimensional (3-D) growth. The GaInNAsSb lasers oscillated under CW operation at 1.258 /spl mu/m at room temperature. The low CW threshold current of 12.4 mA and high characteristic temperature (T/sub 0/) of 157 K were obtained for GaInNAsSb lasers, which is the best result for GaInNAs-based narrow stripe lasers.

1.31 /spl mu/m GaInNAsSb/GaNAs-SQW lasers grown by gas-source MBE

1.31 /spl mu/m GaInNAsSb single quantum-well (SQW) lasers were successfully grown on GaAs substrates by gas-source molecular beam epitaxy (CSMBE). We obtained the very low threshold current density (Jth) of 570 A/cm/sup 2/ at 900 /spl mu/m-long cavity.

1.3 /spl mu/m InAsP-GaInAsP-InGaP strain-compensated MQW lasers grown by GSMBE

We studied strain-compensated MQW lasers which have GaInAsP intermediate layer between 1.45% compressively strained InAsP wells and 0.98% tensile strained InGaP barriers by gas-source MBE. X-ray diffraction measurements revealed that monocrystalline was confirmed even in 15 strained quantum wells. Threshold current density per well in lasers decreased with increasing the number of wells. The temperature characteristics of threshold current density and differential quantum efficiency were improved with increasing the number of wells. The BH lasers which have 15 quantum wells showed excellent performance such as low threshold current (5.2 mA@ 20/spl deg/C) and high T/sub o/ (75 K@ 20/spl deg/C-70/spl deg/C).

1.3 μm InAsP p-type modulation doped MQW lasers grown by gas-source molecular-beam epitaxy

We investigated the effect of p-type modulation doping on the laser performance in 1.3 μm InAsP compressively strained MQW lasers grown by gas-source molecular beam-epitaxy (GSMBE) for the first time. A sharp modulation doping profile of beryllium was confirmed by secondary ion mass spectroscopy. A very low threshold current of 6 mA was obtained for buried heterostucture lasers doped with 5 x 10 18 cm -3 of 300 μm-long cavity with cleaved facets. By using p-type MD-MQW lasers, the gain coefficient was confirmed to increase by about 100 cm - 1 compared to undoped MQW lasers from the measurement of cavity length dependence of threshold current density. Further, differential gain was confirmed to increase by a factor of 1.34 from the relative intensity noise spectrum.