T. R. Chen

The optical gain lever: A novel gain mechanism in the direct modulation of quantum well semiconductor lasers

A new gain mechanism active in certain quantum well laser diode structures is demonstrated and explained theoretically. It enhances the modulation amplitude produced by either optical or electrical modulation of quantum well structures. In the devices tested, power gains of 6 dB were measured from low frequency to frequencies of several gigahertz. Higher gains may be possible in optimized structures.

Submilliampere threshold current pseudomorphic InGaAs/AlGaAs buried-heterostructure quantum well lasers grown by molecular beam epitaxy

We report on low threshold current strained InGaAs/AlGaAs single quantum well lasers grown by molecular beam epitaxy. Broad-area threshold current densities of 114 A/cm2 at 990 nm were measured for 1540-µm-long lasers. Threshold currents of 2.4 mA at 950 nm were obtained for an uncoated buried-heterostructure device with a 2-µm-wide stripe and 425-µm-long cavity. With reflective coatings the best device showed 0.9 mA threshold current (L=225 µm). Preliminary modulation measurements show bandwidths up to 5.5 GHz limited by the detector response.

Low-threshold and high-temperature operation of InGaAlAs-InP lasers

InGaAlAs-InP strained multiquantum-well ridge waveguide laser diodes operating at 1300 nm and exhibiting excellent performance have been fabricated. Threshold currents as low as 3.9 mA and T/sub 0/ values as high as 120 K have been measured. These values are the best reported thus far for this material system.

Effect of state filling on the modulation response and the threshold current of quantum well lasers

The influence of state filling (carrier population of upper subbands of quantum well laser structures) on the optical gain constant is analyzed in conventional separate confinement quantum well lasers. We find that the appreciable population in the states of the optical confinement layers causes a significant lowering of the differential gain. It is pointed out that strain induced reduction of state‐filling effects is a probable cause of improved performance in the tensile strained quantum well lasers. The strategy of design for very high frequency and very low threshold current quantum well lasers is addressed.

Quantum well superluminescent diode with very wide emission spectrum

Superluminescent diodes (SLDs) employing single and multiple quantum wells were investigated. The diode structure includes a monolithic window and a gain and absorber section. Spectral widths 2–3 times that of conventional SLDs were demonstrated.

Direct measurement of linewidth enhancement factors in quantum well lasers of different quantum well barrier heights

The wavelength dependence of the linewidth enhancement factor (amplitude‐phase coupling factor) α in quantum well lasers of different quantum well barrier heights have been determined from the spontaneous emission spectra and the Fabry–Perot mode wavelength shifts. It is found that the α parameter at lasing wavelength in GaAs/Al0.15Ga0.85As lasers is about twice as large as that in GaAs/Al0.30Ga0.70As lasers. The observation is consistent with the previously observed spectral linewidth behavior in these lasers, which were attributed to the different state filling effects.

Direct measurement of the carrier leakage in an InGaAsP/InP laser

Carrier leakage over the heterobarrier in an InGaAsP/InP laser is measured directly in a laser-bipolar-transistor structure. Experimental results indicate a significant amount of carrier leakage under normal laser operating conditions.

High efficiency single quantum well graded‐index separate‐confinement heterostructure lasers fabricated with MeV oxygen ion implantation

Single quantum well AlGaAs/GaAs graded-index separate-confinement heterostructure lasers have been fabricated using MeV oxygen ion implantation plus optimized subsequent thermal annealing. A high differential quantum efficiency of 85% has been obtained in a 360-µm-long and 10-µm-wide stripe geometry device. The results have also demonstrated that excellent electrical isolation (breakdown voltage of over 30 V) and low threshold currents (22 mA) can be obtained with MeV oxygen ion isolation. It is suggested that oxygen ion implantation induced selective carrier compensation and compositional disordering in the quantum well region as well as radiation-induced lattice disordering in AlxGa1–xAs/GaAs may be mostly responsible for the buried layer modification in this fabrication process.

Monolithic integration of a very low threshold GaInAsP laser and metal‐insulator‐semiconductor field‐effect transistor on semi‐insulating InP

Monolithic integration of 1.3‐μm groove lasers and metal‐insulator‐semiconductor field‐effect transistors (MISFET) is achieved by a simple single liquid phase epitaxy (LPE) growth process. Laser thresholds as low as 14 mA for 300‐μm cavity length are obtained. MIS depletion mode FET’s with n channels on LPE grown InP layer show typical transconductance of 5–10 mmho. Laser modulation by the FET current is demonstrated at up to twice the threshold current.

Carrier leakage and temperature dependence of InGaAsP lasers

A direct measurement of electron and hole leakage in InGaAsP/InP lasers has been carried out. The effect of electron leakage on the temperature sensitivity of InGaAsP/InP lasers has been revealed.