Yasuhiko Arakawa

Quantum well lasers--Gain, spectra, dynamics

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.

Theory of gain, modulation response, and spectral linewidth in AlGaAs quantum well lasers

We investigate theoretically a number of important issues related to the performance of AlGaAs quantum well (QW) semiconductor lasers. These include a basic derivation of the laser gain, the linewidth enhancement factor α, and the differential gain constant in single and multiple QW structures. The results reveal the existence of gain saturation with current in structures with a small number of wells. They also point to a possible two-fold increase in modulation bandwidth and a ten-fold decrease in the spectral laser linewidth in a thin QW laser compared to a conventional double heterostructure laser.

Quantum noise and dynamics in quantum well and quantum wire lasers

We calculate the relaxation oscillation corner frequency fr and the linewidth enhancement factor alpha for both a quantum well and a quantum wire semiconductor laser. A comparison of the results to those of a conventional double heterostructure device indicates that fr can be enhanced by 2× in the quantum well case and 3× in the quantum wire case while alpha is reduced in both cases.

Second quantized state lasing of a current pumped single quantum well laser

Newly observed features of quantum well lasers are presented and explained with the aid of a simple model. These involve lasing with gain contributions not only from the fundamental (n=1) state, but simultaneously from the second quantized (n=2) state as well. Experimental data for current pumped GaAlAs/GaAs single quantum well lasers are presented. Very high resonator losses (≳100 cm−1) force the lasers to augment their gain with major contributions from the second quantized state. The main signature of n=2 lasing, a sudden and large increase in the lasing photon energy, is observed and explained by the theory.

Dose‐dependent mixing of AlAs‐GaAs superlattices by Si ion implantation

The effects of Si ion implantation and annealing on AlAs‐GaAs superlattices are examined with secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS), and transmission electron microscopy (TEM). Samples implanted with 180 keV 28Si+ of doses ranging from 3×1013 to 3×1015 cm−2 are examined before and after a 3‐h 850 °C anneal. Both the TEM and RBS channeling data indicate the formation of a heavily damaged surface layer where diffusion of Al is inhibited even after thermal annealing. After annealing, however, significant mixing is observed at depths well beyond the implant range. Depth‐dependent diffusion lengths of Al and Si are derived from the SIMS data. The diffusion coefficient of Si is markedly reduced in the unmixed regions with both the Si and Al concentrations exhibiting abrupt forward and rear diffusion fronts.

Active Q switching in a GaAs/AlGaAs multiquantum well laser with an intracavity monolithic loss modulator

Active Q switching in a GaAs/AlGaAs multiquantum well laser with an intracavity electroabsorption monolithic loss modulator is demonstrated. In this device, an efficient loss modulation is achieved through the quantum confined Stark effect in a modulator section and the enhanced carrier induced band shrinkage effect in an optical amplifier section. It is found that a picosecond pulse as narrow as 18.6 ps full width at half‐maximum is generated and a high repetition rate of more than 3 GHz is obtained.

Enhanced modulation bandwidth of GaAlAs double heterostructure lasers in high magnetic fields: Dynamic response with quantum wire effects

The modulation bandwidth of GaAlAs double heterostructure (DH) lasers in high magnetic fields is measured. We found that the modulation bandwidth is enhanced by 1.4× with a magnetic field of 20 T. This improvement is believed to result from the increase of the differential gain due to two-dimensional carrier confinement effects in the high magnetic field (quantum wire effects). A comparison of the experimental results with a theoretical analysis indicates that the intraband relaxation time tauin of the measured DH laser in the range of 0.1 to 0.2 ps.

Fermi energy dependence of linewidth enhancement factor of GaAlAs buried heterostructure lasers

The linewidth enhancement factor α is measured in a number of GaAlAs lasers with different internal losses. It is found that α decreases monotonically with the increase of the loss (Fermi energy level) in agreement with the theoretical prediction. On the basis of these results the design of cavity length and mirror reflection in order to reduce the spectral linewidth of the laser output is discussed.

Reduction of the spectral linewidth of semiconductor lasers with quantum wire effects—Spectral properties of GaAlAs double heterostructure lasers in high magnetic fields

The spectral linewidth of a GaAlAs double heterostructure laser placed in a high magnetic field is measured at 190 K. It is found that the power-dependent spectral linewidth is reduced by a factor of 0.6 in a magnetic field of 19 T. This reduction is believed to result mainly from the reduction of the linewidth enhancement factor alpha due to a quasi-one-dimensional electronic system formed by the high magnetic field (i.e., by quantum wire effects).

Dynamic and spectral properties of semiconductor lasers with quantum-well and quantum-wire effects

Abstract Our recent studies of the dynamic and spectral properties of semiconductor lasers with quantum-well or quantum-wire structures are described. We have predicted a two-fold increase in the modulation corner frequency of a multiquantum-well laser as compared to the conventional laser; a threefold increase in this quantity is predicted for the multiquantum-wire laser. Improvement of the spectral linewidth in the single quantum-well and single quantum-wire cases is also predicted. Enhancement of the modulation corner frequency in a quantum-wire laser is experimentally demonstrated by operation of a conventional laser in magnetic fields up to 20 Tesla. A corner frequency enhancement of 1.5 × has been observed.