K. Wakao

Planar‐embedded InGaAsP/InP heterostructure laser with a semi‐insulating InP current‐blocking layer grown by metalorganic chemical vapor deposition

We used metalorganic chemical vapor deposition to fabricate a planar‐embedded InGaAsP/InP heterostructure laser with a semi‐insulating InP current‐blocking layer. The laser exhibits cw operation with a low, 20 mA threshold current and a high external differential quantum efficiency of 40% at room temperature. Measurements have also shown a small‐signal frequency response of 10 GHz due to an extremely small parasitic capacitance of 3.5 pF.

Catastrophic degradation of InGaAsP/InGaP double‐heterostructure lasers grown on (001) GaAs substrates by liquid‐phase epitaxy

Catastrophically degraded InGaAsP/InGaP double‐heterostructure lasers grown on (001) GaAs substrates by liquid‐phase epitaxy, emitting at 727 and 810 nm are investigated by photoluminescence topography, scanning electron microscopy, transmission electron microscopy, and energy dispersive x‐ray spectroscopy. The degradation is mainly due to catastrophic optical damage at the facet, i.e., development of 〈110〉 dark‐line defects from the facet, and rarely due to catastrophic optical damage at some defects, i.e., development of 〈110〉 dark‐line defects from the defects inside the stripe region. These 〈110〉 dark‐line defects correspond to complicated dislocation networks connected with dark knots, and are quite similar to those observed in catastrophically degraded GaAlAs/GaAs double‐heterostructure lasers. The degradation characteristics of the InGaAsP/InGaP double‐heterostructure lasers are rather similar to those in GaAlAs/GaAs double‐heterostructure lasers concerning the catastrophic degradation.

A tunable wavelength-conversion laser

A wavelength-conversion laser was fabricated using monolithic integration of a bistable laser diode and a wavelength-tunable distributed Bragg reflector (DBR) laser. This device converts an input light signal with a certain wavelength to output light with a tunable wavelength over 3.5 nm. Input power required for switching is investigated, and its resonant dependence on input wavelength is revealed. Input polarization is also discussed, and suppression of crosstalk is demonstrated. This devices turn-off switching response is greatly influenced by the light power of the input signal as well as bias current, and the first 1 Gb/s operation is achieved in optimum conditions for fast turn-off and stable turn-on. >

Semi‐insulator‐embedded InGaAsP/InP flat‐surface buried heterostructure laser

A new structure semi‐insulator‐embedded flat‐surface buried heterostructure 1.3 μm InGaAsP/InP laser has been developed using chloride vapor phase epitaxy. cw threshold currents as low as 18 mA and high‐temperature cw operation up to 100 °C have been obtained. Small‐signal response above 4 GHz has been achieved and no remarkable roll‐off has been observed, which is due to small parasitic capacitance.

Defect structures in rapidly degraded InGaAsP/InGaP double‐heterostructure lasers

Rapidly degraded InGaAsP/InGaP double‐heterostructure lasers grown on (001)‐oriented GaAs substrates by liquid phase epitaxy have been investigated by photoluminescence topography and transmission electron microscopy. 〈100〉‐dark‐line defects and 〈110〉‐dark‐line defects are observed in the degraded region. The 〈100〉‐dark‐line defects correspond to interstitial type dislocation dipoles caused by recombination enhanced dislocation climb. Their origins are threading dislocations, V‐shaped dislocations, and dislocation networks. The 〈110〉‐dark‐line defects correspond to faulted dipoles extended from small faulted loops in the active layer, edge dipoles extended from threading dislocations, and glide dislocations. The velocities of the 〈100〉‐dark‐line defects are estimated by the operating time and the length of the dark lines, and are quite similar to those in rapidly degraded GaAlAs double‐heterostructure lasers.

Low threshold current density 1.3-/spl mu/m strained-layer quantum-well lasers using n-type modulation doping

We have developed 1.3 /spl mu/m n-type modulation-doped strained-layer quantum-well lasers. Modulation-doped lasers with long cavities (low threshold gain) exhibit much lower threshold current densities than conventional lasers with undoped barrier layers. The lowest threshold current density we obtained was 250 A/cm/sup 2/ for 1500 /spl mu/m long lasers with five quantum wells. The estimated threshold current density for an infinite cavity length was 38 A/m/sup 2//well. This is the lowest value for InGaAsP-InGaAsP and InGaAs-InGaAsP quantum well lasers to our knowledge.<<ETX>>

Catastrophic degradation level of visible and infrared GaAlAs lasers

Burn‐off output powers of catastrophic failures have been studied for GaAlAs double heterostructure (DH) lasers with facet coatings in the wavelength range of 750–870 nm. It was found that the burn‐off power density does not depend on the lasing wavelength when the laser is operated under pulsed condition, whereas it decreases slightly as the wavelength becomes shorter under cw condition.

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

An internal efficiency of 91% was obtained with In/sub 0.7/Ga/sub 0.3/As/InGaAsP strained-layer multiple quantum well (MQW) lasers emitting at a wavelength of 1.5 mu m. The dependence of the reciprocal differential quantum efficiency on the length of the laser cavity shows that the absorption loss in the InGaAsP ( lambda =1.3 mu m) confinement layer caused by carrier overflowing into the confinement layer reduces the internal efficiency.<<ETX>>

High-speed operation of strained InGaAs/InGaAsP MQW lasers under zero-bias condition

5 High-speed zero-bias operation of 1.5- mu m In/sub 0.62/Ga/sub 0.38/As/In compressively-strained-MQW (multi-quantum-well) lasers at high temperatures is reported. This is achieved by optimizing the SCH (separate confinement heterostructure) composition to minimize the lasing delay time. Using a laser with an optimized SCH composition, zero bias 1-Gb/s modulation at 70 degrees C with a large eye opening time of 700 ps is demonstrated. In the optimization, strong carrier lifetime dependence on the SCH composition is observed. To see this dependence more precisely, the SCH structure dependence of effective carrier recombination coefficient B, which is an essential parameter for the carrier lifetime, has been experimentally investigated. >

InGaAsP/InP planar buried heterostructure lasers with semi-insulating InP current blocking layers grown by MOCVD

InGaAsP/InP planar buried heterostructure (BH) lasers with semi-insulating current blocking layers have been realized using LPE and MOCVD hybrid growth. The planar structure has been obtained by developing the selective embedding growth in MOCVD. Low threshold current of 17 mA and high efficiency of 42 percent have been attained with the BH lasers. Small-signal modulation bandwidth of 10 GHz has also been achieved.