InAs self-assembled quantum dots by utilizing a thin GaAs insertion layer (IL) on a 1nm thick AlAs seed layer were grown on GaAs(100) substrates by using a molecular beam epitaxy technique. InAs quantum dots (QDs) were formed by varying the thickness of the GaAs IL from 1 to 9 ML (monolayer), and their morphological and optical properties were characterized by atomic force microscopy and photoluminescence (PL). As a result, when the GaAs IL was thicker than 5 ML, normal InAs QDs with an average diameter of 30nm and a density of 2×1010∕cm2 were formed, because the enhanced surface roughness due to the AlAs layer was leveled by the GaAs IL. However, when the thickness of the GaAs IL was decreased from 5 to 3 ML, the formed InAs QDs showed a bimodal size distribution, i.e., large dots with a lateral size of about 30nm and small dots with that of about 20nm. When the GaAs IL was below 1 ML, InAs QDs with an average diameter of less than 15nm and a high density of 1.5×1011∕cm2 were grown. Consequently, it was verified that the thickness parameter of the GaAs IL had an effect on the size distribution of InAs QDs. Furthermore, although the AlAs layer was used for the purpose of improving the density of the QDs, their PL intensity was comparable to that of the normal InAs QDs.
A highly sensitive photodetector, which is fabricated on a silicon-on-insulator metal oxide semiconductor field-effect transistor (SOI MOSFET) with a nanometer-scale wire, is proposed and optical responses are studied. Experimental results show that our device has a responsivity of 36 A/W, which is significantly higher than that of the conventional SOI MOSFET, and a significantly lower dark current. Interestingly, the photodetector with wire also shows pseudo kinks in a fully depleted type. We consider that these phenomena are affected by the wire, and the physical mechanism of the operation of our photodetector is explained by a strong lateral bipolar action. The linearity with optical power and spectral response in the visual spectral range are presented. Our device can be easily downscaled below 0.1 µm without the loss of sensitivity and the increase in dark current.
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