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We have studied the effect of geometric factors on the polarization properties of verticalcavity surface-emitting lasers with tilted pillar structures. Laser pillars with circular, square, diamond, and rectangular shapes were formed using reactive ion beam etching, by tilting the substrate with an angle of 15° ∼ 30° toward the  or  direction. We measured the polarization characteristics for the devices of 10 ∼ 20 atm size. We observed that an effective geometric factor on the polarization selectivity in tilted pillar structures is an asymmetric shape of vertical-cavity rather than an anisotropic shape of device area in planar direction.
We report successful application of a low-temperature-grown amorphous GaAs (a-GaAs) layer for stabilization of the fundamental transverse mode of InGaAs/GaAs vertical-cavity surface-emitting lasers. The maximum currents maintaining a stable fundamental transverse mode were increased by the antiguide effect of a-GaAs with a high refractive index. For 10-μm- and 15-μm-diameter devices, we attained a stable single-mode emission over a wide range of current. The antiguiding of transverse modes in vertical cavity buried in the high refractive cladding layer was calculated using a two-dimensional beam propagation method.
We performed a polarization control method for vertical-cavity surface-emitting lasers by tilted-etching of the air-post. Circular laser posts were etched by tilting the substrate toward  or  direction with an angle of 15° ˜ 20° using reactive ion beam etching. For the laser devices with a diameter of 7 ˜ 10 μm, we observed outstanding selectivity of the polarization state. We found a dominant polarization perpendicular to the tilted direction. The maximum orthogonal polarization suppression ratio was about 25 dB. The selectivity of polarization in the tilted laser post devices is interpreted to be originated from the difference of optical losses of the two waves polarized to the  and  directions.
We report for the first time a successful application of semi-insulating amorphous GaAs layer for surface passivation of index-guided vertical-cavity surface-emitting lasers. The amorphous GaAs layers on ion-beam-etched active region and mirror layers provide a significant improvement, more than 20%, in the threshold current density and differential quantum efficiency. The improvement of these performances is attributed to low defect density at the surface of active layers induced by amorphous GaAs.
The effects of hydrogen plasma exposure upon electron Hall mobilities in InSb heteroepitaxial film grown on GaAs substrate have been investigated. After exposure to a hydrogen plasma at 250°C, the electron Hall mobility is significantly increased at low temperatures and the temperature dependence of the mobility is reduced. For the film with a broad x-ray rocking-curve width, 4 h-hydrogen plasma exposure can give rise to the enhancement of the mobility up to 6 times at low temperature. The mobility for the film with a narrow line width is enhanced around 1.5 times. These enhanced mobilities are nearly restored by 350°C rapid thermal annealing. The enhancement of the mobility due to hydrogenation is attributed to the satisfaction of the dangling bonds generated by the misfit dislocations.
We present preliminary results aimed at investigating the effects of unprecracked arsine and trimethylgallium on the CBE (chemical beam epitaxy) growth of GaAs epilayers. We find that the growth rate rises linearly as the V/III ratio is increased when TMGa and arsine are used. All of the runs produced p-type material mainly due to carbon incorporation with the hole concentration typically of 1017 cm−3. The impurity content of the layers was found to depend distinctly on the pressure of TMGa. The significant drop in hole concentration is due in part to the hydrogen atoms generated from decomposed AsH3 which then aids in the removal of CH3 radicals on the surface. As a result of using unprecracked arsine for growth of the GaAs epilayers, we measure substantial improvements in their electrical and optical properties.
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