We discuss a number of theoretical and experimental issues in quantum well lasers with emphasis on the basic behavior of the gain, the field spectrum, and the modulation dynamics It is revealed that the use of quantum well structures results in improvement of these properties and brings several new concepts to optical semiconductor devices

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Quantum well lasers--Gain, spectra, dynamics

The linear gain and the intervalence band absorption are analyzed for quantum-well lasers. First, we analyze the electronic dipole moment in quantum-well structures. The dipole moment for the TE mode in quantum-well structures is found to be about 1.5 times larger at the subband edges than that of conventional double heterostructures. Also obtained is the difference of the dipole moment between TE and TM modes, which results in the gain difference between these modes. Then we derive the linear gain taking into account the intraband relaxation. As an example, we applied this analysis to GaInAs/InP quantum-well lasers. It is shown that the effects of the intraband relaxation are 1) shift of the gain peak toward shorter wavelength with increasing injected carrier density even in quantum-well structures, 2) increase of the gain-spectrum width due to the softening of the profile, and 3) reduction in the maximum gain by 30-40 percent. The intervalence band absorption analyzed for quantum-well lasers is nearly in the same order as that for conventional structures. However, its effect on the threshold is smaller because the gain is larger for quantum wells than conventional ones. The characteristic temperature T 0 of the threshold current of GaInAs/InP multiquantum-well lasers is calculated to be about 90 K at 300 K for well width and well number of 100 A and 10, respectively.

Gain and intervalence band absorption in quantum-well lasers

Metalorganic chemical vapor deposition (MOCVD) is a process in which two or more metalorganic chemicals (for instance, trimethylgallium) or one or more metalorganic sources and one or more hydride sources (for instance, arsine, AsH(3)) are used to form the corresponding intermetallic crystalline solid solution MOCVD materials technology is a vapor-phase growth process that is becoming widely used to study the basic physics of novel materials and to grow complex semiconductor device structures for new optoelectronic and photonic systems The MOCVD process is described and some of the device applications and results that have been realized with it are reviewed, with particular emphasis on the III-V compound semiconductors

Metalorganic Chemical Vapor Deposition of III-V Semiconductors

The metalorganic chemical vapor deposition (MOCVD) of epitaxial III‐V semiconductor alloys on III‐V substrates is reviewed in detail. The emphasis is placed on both practical and theoretical knowledge of the equipment and deposition process. The chemistry of the source alkyls and the dynamics of the transport process are discussed. The growth of the GaAs and AlxGa1−xAs systems are treated as prototypical examples (and the most studied) of the III‐V materials. Latter sections review InP, Ga1−xInxAs, and related alloys. Finally, the antimonide and the other systems are reviewed. Electronic and optical devices fabricated from MOCVD‐grown materials are used as examples of the capabilities of the growth technique.

Metalorganic chemical vapor deposition of III‐V semiconductors

This review covers a spectrum of optoelectronic properties of and uses for semi-insulating semiconductor heterostructures and thin films, including epilayers and quantum wells. Compensation by doping, implantation, and nonstoichiometric growth are described in terms of the properties of point defects and Fermi level stabilization and pinning. The principal optical and optoelectronic properties of semi-insulating epilayers and heterostructures, such as excitonic electroabsorption of quantum-confined excitons, are described, in addition to optical absorption by metallic or semimetallic precipitates in these layers. Low-temperature grown quantum wells that have an arsenic-rich nonstoichiometry and a supersaturated concentration of grown-in vacancies are discussed. These heterostructures experience transient enhanced diffusion and superlattice disordering. The review discusses the performance of optoelectronic heterostructures and microcavities that contain semi-insulating layers, such as buried heterostructure stripe lasers, vertical cavity surface emitting lasers, and optical electroabsorption modulators. Short time-scale applications arise from the ultrashort carrier lifetimes in semi-insulating materials, such as in photoconductors for terahertz generation, and in saturable absorbers for mode-locking solid state lasers. This review also comprehensively describes the properties and applications of photorefractive heterostructures. The low dark-carrier concentrations of semi-insulating heterostructures make these materials highly sensitive as dynamic holographic thin films that are useful for adaptive optics applications. The high mobilities of free carriers in photorefractive heterostructures produce fast dielectric relaxation rates that allow light-induced space-charge gratings to adapt to rapidly varying optical fringe patterns, canceling out environmental noise during interferometric detection in laser-based ultrasound, and in optical coherence tomography. They are also the functional layers in high-sensitivity dynamic holographic materials that replace static holograms in Fourier imaging systems and in experimental Tbit/s optical systems. Semi-insulating heterostructures and their applications have attained a degree of maturity, but many critical materials science issues remain unexplored.

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Semi-insulating semiconductor heterostructures: Optoelectronic properties and applications

Optical gain characteristics of quantum well heterostructure lasers are investigated in a broad range from a weakly quantized system to a strongly quantized one utilizing the band-to-band model with k selection rule, the detailed band structure of the quantum well heterostructures, and degenerate statistics. The results are compared to the experimentally observed threshold current densities in graded barrier single quantum well lasers. It is found that the threshold current densities of these quantum well lasers are well explained by the theoretical results in the range of well width from 75 to 300 A. The lowest threshold current density observed is 245 A/cm2in a heavily doped 100 A single quantum well laser with a 150μm stripe width and 550μm length.

Graded barrier single quantum well lasers - Theory and experiment

Graded‐barrier GaAs‐GaAlAs single quantum well lasers have been fabricated, utilizing the graded‐index separate confinement heterostructure to confine carriers and optical field. Very low threshold current densities have been observed down to a well size of 75 A. The lowest threshold current density observed is 240 A/cm2 for a 100‐A heavily doped quantum well laser. This experimental value agrees very well with the calculated threshold current density obtained from detailed band calculation and is attributed to the enhanced gain‐current characteristic in these quantum well structures.

Very narrow graded‐barrier single quantum well lasers grown by metalorganic chemical vapor deposition

In this paper we report and analyze some interesting properties observed for gain-guided GB-SQW lasers. For narrow stripe widths ( \leq10 \mu m) and thin active layers (≤150 A) we observe a long delay time for lasing and abnormal increase in threshold current density. To explain this behavior we developed a model of waveguiding that takes into account the effect of heat profile generated along the junction plane due to carrier injection, and good agreement with experimental results is obtained.

Waveguiding, spectral, and threshold properties of a stripe geometry single quantum well laser

We have observed the presence of very long delay times (~ 1 µs) for lasing in graded barrier single-quantum-well (GB-SQW) lasers for active layers thinner than 150 A and stripe widths below approximately 10 µm. It is shown that an explanation of this phenomenon based on the dynamic evolution of the waveguide properties of these lasers gives good agreement with experimental results.

Long delay time for lasing in very narrow graded barrier single-quantum-well lasers

The fabrication of an integrated optoelectronic transmitter consisting of an MOCVD-grown quantum-well laser and ion-implanted metal-semiconductor field-effect transistors (MESFETs) is described. The transmitter is characterised by a laser threshold current of 30 mA, differential quantum efficiency of 50%, MESFET transconductance of 60 mS/mm, and operation at frequencies up to 2 GHz.

Integrated quantum-well-laser transmitter compatible with ion-implanted GaAs integrated circuits

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