L. E. Eng

108 GHz passive mode locking of a multiple quantum well semiconductor laser with an intracavity absorber

A two‐section multiple quantum well laser is passively mode locked without an external cavity at ∼108 GHz. The pulse widths average 2.4 ps and have a time‐bandwidth product of 1.1. Self‐pulsations at frequencies up to 8 GHz are also observed.

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.

Submilliamp threshold InGaAs-GaAs strained layer quantum-well laser

Strained-layer InGaAs-GaAs single-quantum-well buried-heterostructure lasers were fabricated by a hybrid beam epitaxy and liquid-phase epitaxy technique. Very low threshold currents, 2.4 mA for an uncoated laser (L=425 mu m) and 0.75 mA for a coated laser (R approximately 0.9, L=198 mu m), were obtained. A 3-dB modulation bandwidth of 7.6 GHz was demonstrated at low bias current (14 mA). Procedures for material preparation and device fabrication are introduced. >

Direct determination of the ambipolar diffusion length in GaAs/AlGaAs heterostructures by cathodoluminescence

A new technique for determining carrier diffusion lengths by cathodoluminescence measurements is presented. The technique is extremely accurate and can be applied to a variety of structures. Ambipolar diffusion lengths are determined for GaAs quantum well material, bulk GaAs, Al0.21Ga0.79As, and Al0.37Ga0.63As. A large increase in the diffusion length is found for Al0.37Ga0.63As and is attributed to an order of magnitude increase in lifetime.

Supermode control in diffraction‐coupled semiconductor laser arrays

Supermode control is demonstrated theoretically and experimentally in diffraction‐coupled semiconductor laser arrays. A linear theory is presented to determine the supermode threshold gain as a function of the coupling cavity length. By fabricating devices with different coupling cavity lengths, array operation in both the fundamental and highest order supermodes is achieved.

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.

Effect of Al mole fraction on carrier diffusion lengths and lifetimes in AlxGa1−xAs

The ambipolar diffusion length and carrier lifetime are measured in AlxGa1−xAs for several mole fractions in the interval 0<x<0.38. These parameters are found to have significantly higher values in the higher mole fraction samples. These increases are attributed to occupation of states in the indirect valleys, and supporting calculations are presented.

Cavity length dependence of the wavelength of strained‐layer InGaAs/GaAs lasers

The lasing wavelength of a strained‐layer InGaAs/GaAs single quantum well laser has been found to depend strongly on the cavity length. The relationship between the lasing wavelength and the cavity length was established experimentally and a cavity length tuning mechanism for a quantum well laser is thus made possible.

Strained single quantum well InGaAs lasers with a threshold current of 0.25 mA

Strained layer single quantum well InGaAs lasers with a record low threshold current of 1 mA for as‐cleaved facets and 0.25 mA with high reflectivity coated facets have been demonstrated. In addition, these lasers display a weak dependence of threshold current, quantum efficiency, and lasing wavelength on cavity length in comparison with those single quantum well lasers previously reported.

Microampere threshold current operation of GaAs and strained InGaAs quantum well lasers at low temperatures (5 K)

The operation of ultralow threshold current GaAs and InGaAs quantum well lasers at cryogenic temperatures has been studied. In particular the threshold current Ith and lasing wavelength of GaAs and strained InGaAs lasers have been measured as a function of temperature from 300 down to 5 K. Ith can in both lasers be characterized by a linear function of temperature up to 200 K, with a significantly (2.5×) larger dIth/dT for the GaAs laser. We measured a minimum threshold current of 120 μA for the GaAs laser and 165 μA for the InGaAs laser at 5 K. We derive a simple expression for the transparency carrier density as a function of temperature and effective masses to explain our results.