Quantum Well Intermixing For Photonic Integrated Circuits

Various applications of quantum-well intermixing, ranging from multiwavelength lasers to complex photonic integrated circuits, are described. The fabrication of these GaAs-AlGaAs-based devices relies on the postgrowth definition of regions with varying bandgap, enabling the manufacture of wavelength shifted modulators and lasers, as well as the integration of transparent waveguides with absorbing lasers and detectors. The impurity-free vacancy-enhanced disordering technique employed, and its integration with existing process technologies, will be presented, and examples of multicolor lasers, wavelength shifted modulators and integrated optical interferometers are shown. These applications yield high-optical functionality using relatively simple process and integration technology.

In this thesis, several aspects of GaAsSb/AlSb multiple quantum well (MQW) heterostructures have been studied. First, it was shown that the GaAsSb MQWs with a direct band gap near 1.5μm at room temperature could be monolithically integrated with AlGaSb/AlSb or AlGaAsSb/AlAsSb Bragg mirrors, which can be applied to Vertical Cavity Surface Emitting Lasers (VCSELs). Secondly, an enhanced photoluminescence from GaAsSb MQWs was reported. The photoluminescence strength increased dramatically with arsenic fraction as conjectured. The peak photoluminescence from GaAs0.31Sb0.69 was 208 times larger than that from GaSb. Thirdly, the strong photoluminescence from GaAsSb MQWs and the direct nature of the band gap near 1.5μm at room temperature make the material favorable for intermixing studies. The samples were treated with ion implantation followed by rapid thermal annealing (RTA). A band gap blueshift as large as 198 nm was achieved with a modest ion dose and moderate annealing temperature. Photoluminescence strength for implanted samples generally increased with the annealing temperature. The energy blueshift was attributed to the interdiffusion of both the group III and group V sublattices. Finally, based on the interesting properties of GaAsSb MQWs, including the direct band gap near 1.5μm, strong photoluminescence, a wide range of wavelength (1300 - 1500 nm) due to ion implantation-induced quantum well intermixing (QWI), and subpicosecond spin relaxation reported by Hall et al, we proposed to explore the possibilities for ultra-fast optical switching by investigating spin dynamics in semiconductor optical amplifiers (SOAs) containing InGaAs and GaSb MQWs. For circularly polarized pump and probe waves, the numerical simulation on the modal indices showed that the difference between the effective refractive index of the TE and TM modes was quite large, on the order of 0.03, resulting in a significant phase mismatch in a traveling length larger than 28μm. Thus the FWM conversion efficiency was exceedingly small and the FWM mechanism in SOAs used for investigation of all-optical polarization switching was strongly limited.

Semiconductor Quantum Well Intermixing is an international collection of research results dealing with several aspects of the diffused quantum well (DFQW), ranging from Physics to materials and device applications. The material covered is the basic interdiffusion mechanisms of both cation and anion groups as well as the properties of band structure modifiations. Its comprehensive coverage of growth and pos-growth processing technologies along with its presentation of the various interesting and advanced features of the DFQW materials make this book an essential reference to the study of QW layer intermixing.

SPIE Milestones are collections of seminal papers from the world literature covering important discoveries and developments in optics and photonics.

Quantum well intermixing (QWI), a postgrowth bandgap engineering technology, has been viewed as a promising method for semiconductor photonics integrated circuits (PICs). In this research, we investigated a novel intermixing process that yields large bandgap blueshift at low activation energy in various quantum well and dot structures using metallic impurity induced disordering technique. Large bandgap selectivity and high intermixed material quality have also been observed from GaAs-based quantum well nanostructures. Impurity-free vacancy induced disordering (IFVD), Cu:SiO2 intermixing and nitrogen (N) ion-implantation induced disordering (N-IID) have been performed to promote the efficient group-III intermixing in InP-based quantum dash laser structure. Using Cu:SiO2 and N-IID to promote universal intermixing on dash-inwell InP-based laser structure, up to a maximum bandgap shift of 208 nm (115 meV) and 193 nm (106 meV) were observed from the Cu:SiO2 and N-IIID intermixed samples, respectively.

The term “hybrid silicon laser” refers to a laser that has a silicon waveguide and a III–V material that are in close optical contact. In this structure the optical confinement can be easily transferred from one material to the other and intermediate modes exist for which the light is contained in both materials simultaneously. In hybrid silicon lasers, the optical gain is provided by the electrically pumped III–V material and the optical cavity is ultimately formed by the silicon waveguide. This type of laser can be heterogeneously integrated with silicon components that have superior performance compared to III–V components. These lasers can be fabricated in high volumes as components of complex photonic integrated circuits, largely with CMOS-compatible processes. These traits are expected to allow for highly complex, non-traditional photonic integrated circuits with very high yields and relatively low cost of manufacturing. In this chapter we discuss the theory of hybrid silicon lasers, wafer bonding techniques, examples of experimental results, examples of system demonstrations based on hybrid silicon lasers, and prospects for future devices.