Lasing characteristics of strained quantum well (QW) structures such as InGaAs/AlGaAs on GaAs and InGaAs/InAlAs on InP were analyzed by taking into account the band mixing effect in the valence band. A relaxation oscillation frequency fr, which gives a measure of the upper modulation frequency limit, was found increased three times in a 50 Å In0.9Ga0.1As/In0.52Al0.48As QW structure compared with that in a 50 Å GaAs/Al0.4Ga0.6As QW structure for the undoped case. One of the main factors for this improved frequency bandwidth is attributed to the reduced subband nonparabolicity as well as the reduced valence-band density of state in the strained QW structure. The corresponding lasing threshold current is one order of magnitude smaller than that of the GaAs/AlGaAs QW structure. With a p doping in the QW the fr value increases, and the 3 dB cutoff frequency of about 90 GHz will be expected with an acceptor concentration of 5×1018 cm−3 in the In0.9Ga0.1As/In0.52Al0.48As QW.

Incidence angle effect of a hydrogen plasma beam with an ion energy of about 20 eV was observed in a cleaning process for GaAs and Si surfaces for the first time. An atomically flat (001) GaAs substrate surface which was observed by clear Laue spots was prepared with a glancing angle of incidence. Similar improvement of smoothness was observed with the glancing angle of incidence on a Si surface when it was compared with perpendicular incidence. The mechanism is discussed considering momentum transfer parallel to the surface in the collision process and the resultant migration enhancement on the surface.

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