Effect of Band Tails on Stimulated Emission of Light in Semiconductors
IBM1
TL;DR: The dependence of the stimulated emission of radiation in semiconductors on temperature and impurity concentration has been calculated using a Kane model with a Gaussian band tail for the density of states as discussed by the authors.
Abstract: The dependence of the stimulated emission of radiation in semiconductors on temperature and on impurity concentration has been calculated using a Kane model with a Gaussian band tail for the density of states, and an optical model with a constant matrix element and no selection rule for the radiative transitions The screening length and the characteristic energies for the widths of the conduction- and valence-band tails are calculated by a self-consistent procedure, and the calculation has no adjustable parameters Numerical results are obtained using parameters appropriate for GaAs injection lasers The presence of band tails leads to a more nearly linear dependence of gain on excitation level, in better agreement with experiment, than did the calculation without band tails by Lasher and Stern Increasing impurity concentration leads to a weaker temperature dependence of the excitation rate required to reach a given gain
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TL;DR: In this paper, an analysis of gain suppression in injection lasers with an undoped active region and an index guiding structure is presented. And the results of this analysis explain the experimental data of well-designed injection lasers which have an unweighted active region, which is crucial for the operation of injection lasers in a single longitudinal mode.
Abstract: This paper gives an analysis and discussion of gain suppression in injection lasers which have an undoped active region and an index guiding structure. In previous papers, we used a semiclassical density‐matrix analysis to show that an injection laser with an updoped active region has a nearly, but not perfectly, homogeneous (or uniform) gain property under operating conditions due to the mode coupling effects by phase synchronization of electrons to the lasing field. The gain of adjacent modes is well suppressed by the oscillating mode, and single‐longitudinal‐mode operation is obtained in undoped injection lasers. However, such suppression depends closely on the spacial distribution of the resonating field and injected carrier density. In this paper, the suppression effect is examined theoretically considering electronic intraband relaxation, effects from the standing wave of the lasing field, spatial diffusion of carriers, etc. When the relaxation time is larger than 3×10−13 sec, the gain shows ’’hole burning,’’ namely, strong nonuniformity across the spectral or energy distributions, and, at the same time, the gain of some resonating modes is increased. Single‐longitudinal‐mode operation is not obtained in such a strongly inhomogeneous laser. When the relaxation time is smaller than 2×10−13 sec, the gain can be seen to be nearly homogeneous, and the gain of nonoscillating modes is sufficiently suppressed, that is, lower than that at threshold, because of the strong‐mode‐coupling effect. The relaxation time of GaAs is expected to be approximately 1×10−13 sec, implying 0.1% of excess suppression. The spatial distribution of the resonating field and induced ’’spatial hole burning’’ of carriers tends to increase the gain of higher transverse modes, but only weakly affects the fundamental transverse modes when the oscillating mode is the fundamental mode. It is then necessary to design the laser so that such higher transverse modes are cut off. The results of this analysis explain the experimental data of well‐designed lasers which have an undoped active region and an index guiding structure. Such a gain suppression effect is crucial for the operation of injection lasers in a single‐longitudinal mode.
286 citations
01 Feb 1972
TL;DR: In this paper, a survey of prominent applications for various LEDs is presented, with an emphasis on the III-V semiconducting compounds and GaP LEDs in particular, including photometry, the physics of electrical injection and luminescence.
Abstract: Light-emitting diodes (LEDs) are devices designed to efficiently convert electrical energy into electromagnetic radiation, most of which is visible to the human eye. Some of the disciplines involved in the understanding and utilization of LEDs are reviewed, with emphasis on the III-V semiconducting compounds and GaP LEDs in particular. Salient features of photometry, the physics of electrical injection and luminescence, and the design of LEDs are discussed in detail, followed by a survey of prominent applications for the various LEDs.
258 citations
Abstract: Double heterostructure GaAs–AlxGa1−xAs junction lasers which have very low thresholds and which have been operated continuously at and above room temperature have been fabricated by liquid phase epitaxial growth The threshold current density of these lasers decreases approximately linearly with the thickness of the active region from 3 to at least 05 μm This is interpreted as the result of near perfect carrier and optical confinement as the result of large steps in the energy gap and index of refraction at the heterojunctions in these diodes The gain in these lasers is very high and its dependence upon current density is superlinear Loss is very low and almost that expected from free carriers Complete polarization of the lasing mode was observed This latter is interpreted to be the result of an increased reflection coefficient for the T E mode
178 citations
IBM1
TL;DR: In this paper, the optical gain coefficient as a function of the nominal current density is given for GaAs lasers with compensated n-type active layers and with undoped active layers. And the results suggest that n type layers may give lower threshold currents near room temperature than do comparable p-type layers.
Abstract: Results for the optical gain coefficient as a function of the nominal current density are given for GaAs lasers with compensated n-type active layers and with undoped active layers. The results suggest that n-type layers may give lower threshold currents near room temperature than do comparable p-type layers.
147 citations
TL;DR: In this paper, it was shown that the mirror reflectivity for tightly confined planar waveguide modes becomes a function of both the waveguide and mode parameters, and this dependence plays the dominant role in the selection of the oscillating transverse modes and explains why room-temperature cs-type double-heterostructure lasers tend to lase in higher order TE modes.
Abstract: It is shown that the mirror reflectivity for tightly confined planar waveguide modes becomes a function of both the waveguide and mode parameters. This dependence of the mirror reflectivity plays the dominant role in the selection of the oscillating transverse modes and explains why room‐temperature cs‐type double‐heterostructure lasers tend to lase in higher‐order TE modes. Experimental investigations show that the waveguide and mode parameters are qualitatively consistent with a dielectric step waveguide which is mainly perturbed by small gradients of the optical dielectric constant arising from impurity segregation.
125 citations