With the trend towards miniaturization, micromachining becomes more and more important in fabricating micro parts. Investigations have shown that unpredictable tool life and premature tool failure present a serious concern in micromachining. To further develop the process, a systematic study of various types of tool geometry has been carried out. The tool failure modes and the ways in which tool life can be improved were also studied. Experimental results show that the tool tip rigidity of the semi circle-based (D-type) end-mills is much higher than that of the two-flute (commercial type) end-mills, and the machining quality with the D-type tools is better than that of the triangle-based (-type) end-mills. The tool breakage of end-milling operations simulated using real tool geometry is in good agreement with experimental data. Both the experimental study and FEM analysis have shown that the D-type end-mills are more suitable for micromachining.

We have investigated the electronic band structure and optical transparency conditions of In x Ga 1−x As 1−y N y / GaAs quantum well ͑QW͒ using 10-band, 8-band and 6-band k • p models. The transition energy calculated by the 8-band model agrees very well with the values calculated by the 10-band model, especially in the range of high indium composition ͑35%͒. Electron effective mass ͑m e * ͒ predicated by band anticrossing model, with nitrogen-related enhancement weakened as indium composition increases, was used in the 8-band model and was favored compared to the heavier value predicted by the phenomenological relationship. We have calculated the optical transition matrix element ͑Q i n c n v ͒ using the Bloch wave functions for the k • p models and discovered that the inclusion of nitrogen-related energy level ͑E N ͒ into the calculation of the conduction band by the 10-band k • p model yields lower differential gain ͑dG / dN͒ than that calculated by the 8-band k • p model on the same structure. Contrary to earlier reports that the reduction of dG / dN in In x Ga 1−x As 1−y N y / GaAs QW and thus the lower obtainable optical gain is due to the increase in m e * , we have concluded that the reduction was due to the increased interaction between the ͉S͘ conduction-band state and ͉S N ͘ nitrogen-related energy state, which weaken the optical transition matrix elements between valence band and conduction band. Our results also show that if m e * is very large ͑as predicted by the phenomenological model͒, dG / dN will increase monotonously with nitrogen composition. Moreover, neglecting valence band and conduction band interaction in k • p models will result in the prediction of higher dG / dN which is not accurate.

The effect of annealing on the photoluminescence (PL) in GaAsSbN∕GaAs quantum wells (QWs) grown by solid-source molecular-beam epitaxy has been investigated. The annealing time and temperature are 5min and 650–750°C, respectively. Low-temperature (4K) PL peaks shift to higher energies with the annealing temperatures. An As–Sb atomic interdiffusion at the heterointerface is proposed to model this effect. The compositional profile of the QW after interdiffusion is described by an error function distribution and calculated by a ten-band k∙p method. The estimated interdiffusion constants D are ∼10−17–10−16cm2∕s in the above temperature range and an activation energy of 1±0.4eV is obtained.

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The interdiffusion effect of GaInNAs/ GaAs single quantum well ͑QW͒ has been investigated with the eight-band k • p method. The as-grown 64-Å Ga 0.64 In 0.36 N 0.017 As 0.983 / 250-Å GaAs QW is experimentally determined to emit at 1.27 m in the literature. The compositional profile of the QW after interdiffusion is modeled by an error function distribution. Varying the diffusion length, the effects of interdiffusion on the unstrained band gap, in-plain strain, and confinement profiles are studied. The curve of the ground-state transition ͑C1-HH1͒ energy dependence on the interdiffusion length is obtained. Our work shows that the interdiffusion effect on the strain can greatly change the confinement profile of the lighthole ͑LH͒, which is confined in the GaAs layer, not in the GaInNAs layer. From the transition energy curve, a blueshift of 51 meV is derived. This interdiffusion mechanism can be utilized in the tuning of the laser operation wavelength.