P. L. Derry

Ultralow‐threshold graded‐index separate‐confinement single quantum well buried heterostructure (Al,Ga)As lasers with high reflectivity coatings

Unlike conventional semiconductor lasers, single quantum well lasers with high reflectively coatings have dramatically reduced threshold currents as a result of the smaller volume of the (active) quantum well region. A cw threshold current of 0.95 mA was obtained for a buried graded‐index separate‐confinement heterostructure single quantum well laser with facet reflectivities of ∼70%, a cavity length of 250 μm, and an active region stripe width of 1 μm.

Ultimate limit in low threshold quantum well GaAlAs semiconductor lasers

Gain measurements were performed on buried heterostructure single quantum well lasers to ascertain the transparency current density, which represents a basic limit in the threshold current. By using the optimal design approach, a lowest threshold of 0.55 mA in a 120‐μm‐long device was achieved. Modulation of the low threshold laser by a pseudorandom digital stream at 1.3 Gbit/s without current bias is demonstrated.

High quality molecular beam epitaxial growth on patterned GaAs substrates

In this letter we describe a procedure for high quality molecular beam epitaxy (MBE) growth over finely patterned GaAs substrates which is suitable for device fabrication requiring lateral definition of small (∼1–2 μm) dimension. This method was used for the fabrication of index guided laser arrays. Yields of individual lasers exceeded 90%, and thresholds were uniform to 10%. Temperature and flux ratio dependence of faceting during MBE growth over patterned substrates is shown for temperatures ranging from 580 to 700 °C and for As/Ga flux ratios from 1.4:1 to 4:1. The real index guided structure, which can be formed by a single MBE growth over a ridged substrate, is discussed. This technique should prove useful in the fabrication of devices which take advantage of unique features formed during regrowth by MBE.

High-speed digital modulation of ultralow threshold (<1 mA) GaAs single quantum well lasers without bias

GaAlAs buried heterostructure lasers with submilliampere threshold current fabricated from single quantum well wafers can be driven directly with logic level signals without any current bias. The switch‐on delay was measured to be <50 ps and no relaxation oscillation ringing was observed. These lasers permit fully on‐off multigigabit digital switching while at the same time obviating the need for bias monitoring and feedback control.

Spectral and dynamic characteristics of buried‐heterostructure single quantum well (Al,Ga)As lasers

We demonstrate that, as predicted, (Al,Ga)As single quantum well (SQW) lasers have substantially narrower spectral linewidths than bulk double-heterostructure lasers. We have observed a further major reduction (>3×) in the linewidth of these SQW lasers when the facet reflectivities are enhanced. This observation is explained theoretically on the basis of the very low losses in coated SQW lasers and the value of the spontaneous emission factor at low threshold currents. We also report on the modulation frequency response parameter of these SQW lasers.

High‐speed GaAs/AlGaAs photoconductive detector using a p‐modulation‐doped multiquantum well structure

A new type of high‐speed GaAs/AlGaAs photoconductive detector utilizing the high drift velocity of minority electrons in a p‐modulation doped multiquantum well structure is demonstrated. In this modulation‐doped structure, the electron scattering is reduced, which leads to the enhancement of the electron (minority carrier) drift velocity which determines the response speed of the detector. A deconvolved pulse response as narrow as 33 ps full width at half‐maximum was obtained with an electric field of 3.1 kV/cm at room temperature.

Ultralow threshold graded-index separate-confinement heterostructure single quantum well (Al,Ga)As lasers

Broad area graded‐index separate‐confinement heterostructure single quantum well lasers grown by molecular‐beam epitaxy (MBE) with threshold current density as low as 93 A/cm^2 (520 μm long) have been fabricated. Buried lasers formed from similarly structured MBE material with liquid phase epitaxy regrowth had threshold currents at submilliampere levels when high reflectivity coatings were applied to the end facets. A cw threshold current of 0.55 mA was obtained for a laser with facet reflectivities of ∼80%, a cavity length of 120 μm, and an active region stripe width of 1 μm. These devices driven directly with logic level signals have switch‐on delays <50 ps without any current prebias. Such lasers permit fully on–off switching while at the same time obviating the need for bias monitoring and feedback control.

Applications of a dielectric coating to semiconductor lasers

Abstract Experimental studies and theoretical analyses on the effect of dielectric coatings on semiconductor laser performance are presented. It is demonstrated that the dielectric coating technique is a powerful means of controlling the laser threshold current, external quantum efficiency, maximum output power, longitudinal mode behaviour, lasing wavelength and spectral linewidth.

Broad‐area tandem semiconductor laser

A tandem combination of a uniform gain broad‐area semiconductor laser and a (lateral) periodic gain section displays a stable, near‐diffraction‐limited single‐lobed far‐field pattern. The GaAs/GaAlAs quantum well lasers display a high degree of coherence across 60‐μm‐wide apertures provided that the broad‐area section is sufficiently long.