Heterostructure Injection Lasers Research Articles

Semiconductor laser with beam quality factor M2

Based on the nonparaxial vectorial moment theory of light beam propagation, the beam quality factor M 2 of TE 0 propagating mode for GaAs/Ga 0.7Al 0.3As double heterostructure injection laser is analyzed and calculated. The results show that M 2 can be smaller than unity if the active layer thickness d is smaller than 0.32 times of wavelength, and there is not a low bound for M 2 of semiconductor laser.

Spectral characteristics of single-frequency quantum-well heterolasers

Precision measurements and a comparative analysis were made of the emission spectra of GaAs/AIGaAs and InGaAs/GaAs heterostructure injection lasers with quantum-well active layers and plane—plane cleaved cavities. Attention was focused on the correlation between the linewidth enhancement factor and the parameters of single-frequency lasing. Single-frequency emission at λ = 975 nm was observed for a quantum-well laser with strained active layers and a cw output power in excess of 100 mW was reached when the side longitudinal modes were suppressed by more than 30 dB.

Spectral investigation of the radiation emitted by strained InGaAs/GaAlAs quantum-well heterostructures

The spectral-threshold characteristics were determined in the 980 nm range for InGaAs/GaAlAs quantum-well heterostructure injection lasers. These lasers had a GaAs substrate and an anisotropically strained active layer. A systematic study was made of the spectra of subthreshold spontaneous radiation emitted at temperatures in the range 77–300 K. The dependence of the laser photon energy hν on the threshold current density consisted of two sections: the value of hν increased strongly with the current density for low-threshold samples, but above 0.6 kA cm-2 the value of hν depended weakly on the current density. This behaviour was attributed to the initial filling of the lower quantum states participating in the 1-1h active transition, followed by filling of the second quantum states of the carriers. The lower states ensured a mode gain of 40–50 cm-1.

Continuous-wave lasing at room temperature in InGaSbAs/GaAlSbAs injection heterostructures emitting in the spectral range 2.2–2.4 μm

Room-temperature cw lasing was achieved in InGaSbAs/GaAlSbAs heterostructure injection lasers emitting in the range 2.2–2.4 μm. A stripe geometry with a ridge waveguide was used. The threshold currents in the cw regime were 80–150 mA at T = 300 K.

Transmission electron microscopy of epitaxial gallium arsenide grown on a variety of silicon substrates by metallorganic chemical vapor deposition

The growth of GaAs layers on silicon substrates is under extensive investigation with a view to achieving the integration of GaAs-based optoelectronic devices with Si integrated circuit technology. The large lattice mismatch between Si and GaAs (-4%) together with the differences in the thermal expansion coefficients between the two materials results in a highly stressed interface. Several different approaches have been undertaken in attempts to reduce the dislocation density of the GaAs layer. The inclusion of graded composition GaAsP ‘buffer’ layers, intermediate Ge layers and the inclusion of strained layer superlattices in the growth regime have been reported by many workers. Growth of GaAs directly on Si has been reported to yield GaAs heteroepitaxial films suitable for electronic applications such as FETs and low threshold AlGaAs/GaAs double heterostructure injection lasers.

Room-temperature operation of InGaAsSb/AlGaSb double heterostructure lasers near 2.2 μm prepared by molecular beam epitaxy

In0.16Ga0.84As0.15Sb0.85/Al0.35Ga0.65Sb double heterostructure injection lasers have been grown by molecular beam epitaxy on (100) GaSb substrates. Room-temperature operation near 2.2 μm wavelength has been achieved under pulsed conditions. Low pulsed threshold current density of 4.2 kA/cm2 and a characteristic temperature of T0∼26 K have been obtained.

Optical and transport properties of a double heterojunction GaAs/AlGaAs injection laser from the shift of the wavelength and the threshold current in a strong magnetic field

Measurements of the shift of the laser emission energy and the threshold current of a GaAs/AlGaAs double heterostructure injection laser with a p-type active layer in DC magnetic fields up to 25 T were carried out at temperatures T=20.3K and T=46.0K. A slight difference ( approximately=7%) in the threshold current was observed between measurements with the magnetic field parallel and perpendicular to the direction of the injection current. A theoretical model containing a density of states function with a magnetic field dependent low energy cut-off and lineshape for the Landau levels was used to analyse the observed behaviour of both the shift of the laser emission energy and the threshold current. From the analysis values of optical and transport parameters such as the mobility mu and the radiative recombination coefficient Br in the active layer and the cavity loss L are obtained.

Cw operation of GaInAsSb/AlGaAsSb lasers up to 190 K

Continuous operation of 2.1 μm wavelength Ga0.84In0.16As0.15Sb0.85 /Al0.27Ga0.73As0.04Sb0.96 double heterostructure injection lasers has been achieved up to a temperature of 190 K for the first time. The laser wafers were grown by liquid phase epitaxy. In pulsed operation, broad area devices with active layer thicknesses of 0.8–1.0 μm exhibited room-temperature threshold current densities as low as 7 kA/cm2.

Modal analysis of IncGaAsP-InP, GaAs/AlGaAs-GaAs, and InGaAsP/AlGaAs-GaAs MIS heterostructure lasers

The transverse modal behavior of Metal-Insulator (Oxide)-Semiconductor (MIS) heterostructure injection lasers is analyzed. MIS structures have been proposed by Jain and Marciniec as an alternate approach to p-n heterojunctions to obtain minority carrier injection and subsequent lasing action. In the modal analysis the MIS structure is treated as an asymmetrical three-layer slab waveguide with appropriate boundary conditions. Numerical computations of electric field strength, intensity and confinement factor P are presented for various GaAs and InP based MIS structures. A comparison of the output characteristics of a GaAs MIS laser with a conventional GaAs p-n double heterostructure laser is also reported.

Reflectivity of TE modes at the facets of buried heterostructure injection lasers

The mode reflectivity of narrow stripe geometry buried-heterostructure GaAs/GaAlAs lasers was computed taking into account lateral confinement, as well as transverse confinement. The reflectivity was found to increase with increasing of the junction width, up to the broad-area value, in contrast to results obtained previously. The differences between the lowest computed reflectivities and the broad-area values were found to be 10-25 percent. Lateral confinement should therefore be considered in cases where single-mode confinement and mode reflectivity are important.

Measurement and analysis of planar stripe-geometry GAIAs/GaAs heterojunction laser wavefronts and their variation with pumping current

The far-field patterns and the wavefronts of planar stripe-geometry GaAIAs/GaAs lasers, as well as their variation with pumping current, have been investigated with the help of apparatus based on the Michelson interferometer. Experimental results were compared to the theoretical model of the planar stripe-geometry heterostructure injection laser, using a dielectrical slab and Epstein layer. The effect of kinks in the output (light/current) characteristics on the laser wavefront was studied.

Optical stability of narrow stripe, proton-isolated AlGaAs double heterostructure lasers with gain guiding

Optically stable, proton-isolated, gain-guided (AlGa)As double heterostructure injection lasers are described. A narrow stripe width (3.5 μm) and a very shallow implantation are employed (1.3 μm from the active layer); this results in a cosh−2-like optical mode of ∼9.0-μm full width at half-maximum. The far-field profiles possess strong sidelobes at high optical output power. The optical material loss coefficient and the antiguiding parameter are derived from the measured far-field profiles, using the theory of gain guiding. Key parameters in the description of the optical mode distribution are calculated for several values of output power.

Stimulated emission from shallow donors localized by a strong magnetic field

From measurements of the energy shift of the laser emission and the threshold current as a function of the magnetic field up to 25 T (DC) and at T = 9 K, localization of the shallow donors in the moderately doped (≈ 1017 cm-3) n-type active layer of a double heterostructure injection laser has been observed. A fit of the measured energy shift of the donor ground state as a function of the magnetic field with theoretical calculated values yields the impurity concentration in the active layer and the carrier density at threshold at B = 0 T.

Radiative characteristics of injection lasers with short resonators

An investigation was made of the threshold, power, and spectral characteristics of radiation emitted by GaAs--AlAs heterostructure injection lasers with double confinement and short (up to 16 ..mu..) plane-parallel resonators. The lasers had mesastripe contacts 10--14 ..mu.. wide. The gain coefficient was a linear function of the pump current density in the gain coefficient range 10--400 cm/sup -1/. The minimum threshold currents in the lasers were 27--30 mA and single-frequency lasing regime was observed right up to pump currents of (1.6--1.7)I/sub th/. The maximum single-frequency output power was 35 mW. It should be possible to retain single-frequency regime in such lasers when the pump current was subjected to high-frequency modulation.

Semiconductor laser sources for optical communication

The paper is a general review of double heterostructure GaAlAs and GaInAsP injection lasers and their application in long-distance optical communication systems. After briefly describing the physics of semiconductor laser operation, the performance of oxide stripe and advanced laser structures at 0.85, 1.3 and 1.55 μm wavelength is discussed. The parameters of greatest importance in optical communication systems such as laser spectrum and modulation response are covered in some detail and estimates of device parameters and manufacturing tolerances are given.The relative merits of the different types of laser for both multimode and single-mode optical fibre systems are then discussed. It is shown that single-mode systems operating close to the dispersion minimum are capable of data rates above 390 Mbit/s over distances of 30 km even when fairly conservative worst case assumptions are made. The key parameters that will allow single-mode systems to operate at data rates of more than 1 Gbit/s over distances of 50 to 100 km are identified.

Temperature dependence of the lasing threshold current of double heterostructure injection lasers due to drift current loss

Contact-limited, ambipolar transport, which describes the drift current behavior of minority carriers not confined to the active layer of double heterostructure injection lasers, is used to predict different behavior than previous calculations for the temperature dependence of the threshold current for lasing. The high-temperature coefficients of some lasers may more easily be explained using the model.

Ambipolar transport in double heterostructure injection lasers

Ambipolar conduction through the electrical confinement layers is shown to influence the properties of some double heterostructure injection lasers. A model of contact-limited ambipolar conduction is consistent with known material parameters of (Al,Ga)As lasers and explains several anomalies in the measured device electrical characteristics. The portion of current lost to lasing due to poor carrier confinement in the active region of injection lasers may be greater than previously expected.

Frequency modulation of GaAlAs injection lasers at microwave frequency rates

Frequency modulation of GaAlAs double heterostructure injection lasers at microwave frequencies is reported for the first time. The lasers are operating at a 0.85 μm wavelength and have been modulated at frequencies up to 2.25 GHz with a modulation index of 2.4. The laser FM modulation is displayed by a high resolution spectral measuring setup comprising a monochromator and a Fabry-Perot interferometer. A simple laser model is presented which allows the static frequency shift of the laser resonance frequency to be calculated as a function of the bias current change. The results are compared with measured data.

Variational Treatment of the Diffraction at the Facet of d.h. Lasers and of Dielectric Millimeter Wave Antennas

This paper presents an accurate variational treatment of the diffraction of TE and TM waves by an abrupt transverse discontinuity in a dielectric waveguide, such as the mirror of a double heterostructure (d.h.) injection laser, or the end plane of a dielectric slab antenna for millimeter waves, under the assumption of small aspect ratio. A matrix representation of the Green's function is derived analytically, in the limit of small efective frequency, for the TE case. For the TM case, the complication introduced by the discontinuity of the transverse electric field across the dielectric interface is discussed in detail. The numerical examples refer to the d.h. laser configuration. Both transverse directions (perpendicular as well as parallel) to the junction are studied. The effect of mode coupling at the mirror of a LOC laser as well as the effect of an antireflection coating are investigated.

700-h continuous room-temperature operation of AlxGa1−xAs-GaAs heterostructure lasers grown by metalorganic chemical vapor deposition

Constant-current continuous room-temperature (∼26 °C) operating times greater than 700 h have been achieved for AlxGa1−xAs-GaAs multiple-quantum-well heterostructure injection lasers grown by metalorganic chemical vapor deposition. One device has shown essentially no degradation in its output characteristics during this time.