Self-assembled erbium arsenide islands in gallium arsenide for photomixer devices

This thesis concerns self-assembled ErAs islands in GaAs and the first application of this material to photomixer devices. Photomixer devices generate coherent submillimeter waves by photoconductive heterodyne mixing and require a photoconductive material with a picosecond response time. In this work the suitability of ErAs islands in GaAs for this application is investigated.; The ErAs based material was grown by molecular beam epitaxy. During growth nanometer-sized ErAs islands form spontaneously. Several layers of ErAs islands separated by GaAs can be stacked on top of each other to form a superlattice. The microstructure of such samples was studied by x-ray diffraction and transmission electron microscopy. The x-ray diffraction data show that single-crystallinity is maintained across the ErAs containing layers. Optical pump-probe experiments were performed in reflection and transmission geometry to study the photocarrier lifetimes of the material. These measurements indicate that photogenerated carriers are captured by the ErAs islands on a subpicosecond time scale and that the capture time is limited by the transport in the GaAs matrix. This capture time can be controlled in a straightforward fashion by adjusting the period of the superlattice. Photomixer devices were fabricated from this material. The device characteristics agreed by and large with the device theory. The ErAs based devices perform comparably to existing photomixer technology. The maximum output power was 200 nW at a frequency of 1 THz. ErAs islands in GaAs therefore provide an alternative to existing photomixer technology.