To imitate the way electrical components evolved from discrete devices to devices integrated on Si platform, the next stage for integrated circuits is to integrate photonic components with electrical components on one chip, with active devices known as optoelectronic integrated circuits (OEIC). An ideal solution for this would be to have an all-Si laser. However due to the indirect bandgap of Si this is difficult to achieve. Therefore attention has been focused on trying to integrate the existing and mature III-V laser technology with Si. The difference in lattice constant between GaAs and Si makes direct, monolithic growth of GaAs on Si difficult due to the generation of high defect densities. But the advances in quantum dot (QD) technology and in III-V buffer layer techniques have led to the improvements of direct growth integration. In this thesis an AlAs nucleation layer (NL) in the place of a GaAs nucleation layer was found to increase the photoluminescence intensity and reduce defect density in active layers. Lasers were fabricated with lower threshold current densities than similar devices with GaAs NL. Lasing operation at 1.28 μm was achieved up to 63 °C with a threshold current density of 675 A/cm2 at room temperature. In addition, Ge-on-Si substrates have been used to demonstrate the lasers on Si substrates with a very low pulsed threshold current density of 64 A/cm2, which is significantly lower than any other laser integrated with Si substrates. Also this was the first demonstration of a CW laser on Si with a threshold current density of 163 A/cm2. Lasers were operated up to 30 °C for CW devices and 84 °C for pulsed devices. The difference in threshold currents and temperature performance between CW and pulsed operation is due to high device resistances caused by a combination of poor contact resistance and the introduction of defects from the Si/Ge interface. In conclusion, lasers on Si substrates have been fabricated with low threshold current densities. A very low threshold current density of 64 A/cm2 has been achieved with a Ge-on-Si device and is the lowest result for any type of Si laser at the time of writing, which shows good potential for future integration with Si electronics.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:668435 |
| Date | January 2015 |
| Creators | Lee, A. D. |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/1468566/ |
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