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

/pdf/quantum-well-lasers-gain-spectra-dynamics-3gftmp6esb.pdf

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

The spectrum of an intensity modulated (IM) and a combined intensity-frequency modulated (IM-FM) monochromatic light source has been generated. The amplitudes of the modulated carrier and the first three pairs of sidebands are plotted showing the influence of IM on an FM signal. The effects of first order chromatic dispersion on the baseband amplitude response and harmonic distortion are determined. The manner in which modulation type and depth, modulating frequency, wavelength, and fiber length alter harmonic distortion is presented. Numerical examples giving the amplitude response of a single-mode fiber system as well as the magnitude of the second- and third-harmonic distortion caused by chromatic dispersion are presented. Based on this material, the limits placed on analog transmission due to chromatic dispersion may be assessed.

Chromatic dispersion induced distortion of modulated monochromatic light employing direct detection

We have observed Stark shifts of quantum well intersubband transitions in a perpendicular electric field. Two samples consisting of 100 and 120 A GaAs quantum wells separated by 350 A AlGaAs barriers showed optical absorption peaks at 11.1 and 13.9 μm, respectively. In an electric field of 36 kV/cm, the 13.9 μm peak shifted to 13.7 μm and the 11.1 μm shifted to 11.0 μm, in good agreement with theoretical calculations. These tunable transitions can be applied to high‐speed infrared light modulators.

Observation of Stark shifts in quantum well intersubband transitions

Improved performance of 1.5- mu m wavelength lasers and laser amplifiers using strained In/sub x/Ga/sub 1-x/As-InGaAsP quantum well devices is reported. The device structures fabricated to study the effects of strained quantum wells on their performance are described. These devices showed TM mode gain, demonstrating the strain-induced heavy-hole-light hole reversal in the valence band. Lasers using these tensile strained quantum wells show higher and narrower gain spectra and laser amplifiers have a higher differential gain compared to compressively strained quantum well devices. Consequently, the tensile strained quantum well lasers show the smallest linewidth enhancement factor alpha =1.5 (compression alpha =2.5) and the lowest K-factor of 0.22 ns (compression K=0.58 ns), resulting in an estimated intrinsic 3 dB modulation bandwidth of 40 GHz (compression 15 GHz). >

High-performance 1.5 mu m wavelength InGaAs-InGaAsP strained quantum well lasers and amplifiers

A direct measurement of electron and hole leakage in InGaAsP/InP lasers has been carried out. The effect of electron leakage on the temperature sensitivity of InGaAsP/InP lasers has been revealed.

/pdf/carrier-leakage-and-temperature-dependence-of-ingaasp-lasers-12g13w0dzq.pdf

Carrier leakage and temperature dependence of InGaAsP lasers

Interband nonradiative Auger recombination in quantum-well InGaAsP/InP heterostructure lasers has been calculated. It is found that the Auger rate is much reduced in the quasi two-dimensional quantum-well lasers. This suggests that the temperature sensitivity of quantum-well InGaAsP lasers is much less than ordinary structures with much higher values of T 0 at around room temperatures.

/pdf/auger-recombination-in-quantum-well-ingaasp-heterostructure-2pd3dhpe8e.pdf

Auger recombination in quantum-well InGaAsP heterostructure lasers

Application of internal photoemission from quantum-well and heterojunction superlattices to infrared photodetectors

The interband Auger recombination lifetimes of two Auger processes have been calculated to correlate measured threshold current densities and carrier lifetimes for InGaAsP and InGaAsSb lasers. Good aggreement with experimental data was obtained for lasers with low nominal threshold current densities. These results demonstrate the importance of Auger recombination in the threshold characteristics of InGaAsP/InP lasers.

/pdf/interband-auger-recombination-in-ingaasp-1bsw4s3lpn.pdf

Interband Auger recombination in InGaAsP

A model calculation for the field and hot carrier enhanced electron leakage in InGaAsP/InP LED's and lasers is presented. The significant influence of the doping level in the P-InP confining layer on leakage current is confirmed.

/pdf/field-and-hot-carrier-enhanced-leakage-in-ingaasp-inp-2n5npimx6v.pdf

L. C. Chiu

Papers

Carrier leakage and temperature dependence of InGaAsP lasers

Auger recombination in quantum-well InGaAsP heterostructure lasers

Application of internal photoemission from quantum-well and heterojunction superlattices to infrared photodetectors

Interband Auger recombination in InGaAsP

Field and hot carrier enhanced leakage in InGaAsP/InP heterojunctions