Indium Arsenide (InAs) Islands on Silicon
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Realization of nanometer-scale semiconductor quantum dot structures has become an important area of research focus in recent years primarily because of the potential of nanometer-scale systems in future device applications. With the conventional silicon technology rapidly moving toward saturation in terms of scalability and complexity of fabrication, semiconductor quantum dot structures hold promise as future electronic devices beyond silicon electronics. Furthermore, developing nanometer-scale quantum dot devices on Si and GaAs substrates offers the possibility of advancing their mature device technologies. As a consequence, InAs/GaAs and Ge/Si heterostructures are currently being investigated extensively to develop nanometer-scale quantum devices. While these structures have been extensively investigated because of the availability of advanced GaAs and Si device technologies and the relative ease of growing self-assembled III–V and Si–Ge nanostructures, the InAs/Si heterostructure offers the possibility of growing direct gap InAs on indirect gap Si and holds considerable promise as a candidate for silicon-based optoelectronics as the incorporation of direct band InAs in silicon could significantly improve the radiation recombination efficiency. Although there is more than 11% lattice mismatch between InAs (6.0583 Å) and silicon (5.4310 Å) making InAs/Si a highly strained system, their closely matched thermal expansion coefficients (InAs: 4.70 × 10− 6 K− 1; Si: 4.68 × 10− 6 K− 1) make InAs/Si a promising heterostructure to grow nanometer-scaled InAs islands. Also, this large lattice mismatch can, in fact, be exploited to grow a high density of InAs islands on silicon surface under optimized growth conditions. Laser structures emitting at 1.013 µm have already been fabricated on silicon substrates using quantum dots of compositional InGaAs alloys as active layers.