A new type of semiconductor laser is studied, in which injected carriers in the active region are quantum mechanically confined in two or three dimensions (2D or 3D). Effects of such confinements on the lasing characteristics are analyzed. Most important, the threshold current of such laser is predicted to be far less temperature sensitive than that of conventional lasers, reflecting the reduced dimensionality of electronic state. In the case of 3D‐QW laser, the temperature dependence is virtually eliminated. An experiment on 2D quantum well lasers is performed by placing a conventional laser in a strong magnetic field (30 T) and has demonstrated the predicted increase of T0 value from 144 to 313 °C.

Multidimensional quantum well laser and temperature dependence of its threshold current

Gain and threshold current density are analyzed for quantum-box lasers where electrons are confined in quantum well three-dimensionally, based on the density-matrix theory of semiconductor lasers with relaxation broadening. The electronic dipole moment and its polarization dependence are first analyzed, and it is shown that the gain becomes maximum when the electric field of light is parallel to the longest side of the quantum box. Calculated gain is about 10 times that of bulk crystal for 100 A × 100 A × 100 A GaAs/Ga 0.8 Al 0.2 As quantum box, and 15 times for Ga 0.47 In 0.53 As/InP quantum box with the same size, respectively. The threshold current density are 45 A/cm2and 62 A/cm2for GRINSCH GaAs/(Ga 0.8 Al 0.2 As-Ga 0.4 Al 0.6 As) and Ga 0.47 In 0.53 As/(Ga 0.28 In 0.72 As 0.6 P 0.4 -InP), respectively, where for the GaInAs/ GaInAsP/InP system the intervalence band absorption and nonradiative recombinations have been assumed to be the same as those obtained for bulk crystals experimentally. These results show the possibility of remarkable reduction in the laser threshold by the quantum-box structures.

Gain and the threshold of three-dimensional quantum-box lasers

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 various features peculiar to the operation of quantum-well semiconductor lasers are described and illustrated with data on single- and multiple-quantum-well Al x Ga 1-x As-GaAs heterostructures grown by metalorganic chemical vapor deposition (MO-CVD). Photo-pumped and p-n diode lasers (injection lasers) are described that are capable of continuous room temperature (CW 300 K) operation. The basic problems of carrier collection, thermalization, and quantum-well band filling are considered and have made clear the limits on single quantum-well laser operation and how these can be overcome with multiple quantum-well active regions. The idea that the steplike density-of-states of a quantum-well heterostructure can improve the operation of a semiconductor laser is shown to be valid. Also, it is shown that phonon participation in the operation of a quantum-well laser, which was not anticipated, is a major (even dominant) effect, with perhaps the phonon emission itself in the compact active region being stimulated. Besides the obvious freedom that quantum-well layers offer in how the active region of a semiconductor laser can be designed, quantum-well lasers are shown to exhibit a lesser sensitivity of the threshold current density on temperature, which is explained in terms of the step-like density-of-states and the disturbed electron and phonon distributions in the quantum-well active regions. Values as high as \sim437\deg C have been obtained for T 0 in the usual expression J_{th}(T) = J_{th}(0) \exp (T/T_{0}) . Since photopumped multiple-quantum-well MO-CVD Al x Ga 1-x As-GaAs heterostructures have operated as CW 300 K lasers with only 5-10 mW of photoexcitation (uncorrected for focusing and window losses, \lambda \sim 5145 A), it is suggested that quantum-well laser diodes can be made that will operate at ∼1 mA or even less excitation.

Quantum-well heterostructure lasers

Semiconductor heterostructures and their implementation into electronic and photonic devices have had tremendous impact on science and technology. In the development of quantum nanoelectronics, one-dimensional (1D) heterostructure devices are receiving a lot of interest. We report here functional 1D resonant tunneling diodes obtained via bottom-up assembly of designed segments of different semiconductor materials in III/V nanowires. The emitter, collector, and the central quantum dot are made from InAs and the barrier material from InP. Ideal resonant tunneling behavior, with peak-to-valley ratios of up to 50:1 and current densities of 1 nA/μm2 was observed at low temperatures.

Nanowire resonant tunneling diodes

The achievement of room‐temperature (300 °K) operation of Ga(1−x)AlxAs‐GaAs double‐heterostructure lasers with active layers of quantum‐well dimensions ∼200 A thick is reported. These devices are grown by metalorganic chemical vapor deposition and exhibit pronounced effects in the spectral and lasing characteristics that are related to the small active region thickness and are the first such effects observed for DH lasers in the GaAlAs‐GaAs system.

Room‐temperature laser operation of quantum‐well Ga(1−x)AlxAs‐GaAs laser diodes grown by metalorganic chemical vapor deposition

We report the performance of GaN p-i-n ultraviolet avalanche photodiodes grown on bulk GaN substrates by metal-organic chemical vapor deposition The low dislocation density in the devices enables low reverse-bias dark currents prior to avalanche breakdown for ∼30μm diameter mesa photodetectors The photoresponse is relatively independent of the bias voltage prior to the onset of avalanche gain which occurs at an electric field of ∼28MV∕cm The magnitude of the reverse-bias breakdown voltage shows a positive temperature coefficient of ∼005V∕K, confirming that the avalanche breakdown mechanism dominates With ultraviolet illumination at λ∼360nm, devices with mesa diameters of ∼50μm achieve stable maximum optical gains greater than 1000 To the best of our knowledge, this is the highest optical gain achieved for GaN-based avalanche photodiodes and the largest area III-N avalance photodetectors yet reported

GaN ultraviolet avalanche photodiodes with optical gain greater than 1000 grown on GaN substrates by metal-organic chemical vapor deposition

Data are presented showing that the threshold current density Jth(T) of quantum‐well AlxGa1−xAs‐GaAs heterostructure laser diodes, grown by MO‐CVD, is less temperature dependent than that of conventional DH lasers. T0 in the usual expression Jth∝exp(T/T0) can be high as 437 °C. This behavior is explained in terms of the steplike density of states and the disturbed electron and phonon distribution functions of the quantum‐well active region.

Temperature dependence of threshold current for quantum‐well AlxGa1−xAs‐GaAs heterostructure laser diodes

Laser operation (4.2–300 °K) of multiple‐quantum‐well AlxGa1−xAs‐GaAs heterostructures on a phonon (LO) sideband ∼36 meV below the lowest confined‐particle transitions is described. Phonon‐sideband laser data are presented on two different metalorganic chemical‐vapor‐deposited (MO‐CVD) quantum‐well heterostructures with four GaAs active regions (Lz∼50 and ∼90 A) coupled by three AlxGa1−xAs (x∼0.35) barriers.

Phonon‐sideband MO‐CVD quantum‐well AlxGa1−xAs‐GaAs heterostructure laser

Data are presented demonstrating continuous 300 K photopumped InP quantum dot (QD) laser operation (656–679 nm) realized by modifying and coupling, via tunneling, an auxiliary InGaP quantum well (QW) to the QDs of an InP–In(AlGa)P–InAlP heterostructure grown by metalorganic chemical vapor deposition. The In0.49Ga0.51P QW coupled to the InP QDs by a thin (≲20 A) In0.5Al0.3Ga0.2P barrier overcomes the limitations of carrier collection, lateral transport, and thermalization in the QDs, thus yielding a different form of QD laser.

R. D. Dupuis

Papers

Room‐temperature laser operation of quantum‐well Ga(1−x)AlxAs‐GaAs laser diodes grown by metalorganic chemical vapor deposition

GaN ultraviolet avalanche photodiodes with optical gain greater than 1000 grown on GaN substrates by metal-organic chemical vapor deposition

Temperature dependence of threshold current for quantum‐well AlxGa1−xAs‐GaAs heterostructure laser diodes

Phonon‐sideband MO‐CVD quantum‐well AlxGa1−xAs‐GaAs heterostructure laser

Room-temperature continuous photopumped laser operation of coupled InP quantum dot and InGaP quantum well InP–InGaP–In(AlGa)P–InAlP heterostructures