Compound semiconductor materials and processing technologies for photonic devices and photonics integration
Time: Fri 2020-10-30 10.00
Location: zoom link for online defence (English)
Subject area: Information and Communication Technology
Doctoral student: Carl Reuterskiöld Hedlund , Integrerade komponenter och kretsar
Opponent: Professor Harri Lipsanen,
Supervisor: Mattias Hammar, Integrerade komponenter och kretsar, Mikroelektronik och informationsteknik, IMIT, Elektronik; Mikael Östling, Integrerade komponenter och kretsar; Sebastian Lourdudoss, Fotonik, Mikroelektronik och informationsteknik, IMIT, Elektronik
The advancement of semiconductor optoelectronics relies extensively on materials and processing technologies of ever-increasing sophistication, such as nanometer-range lithography, epitaxial growth methods with monatomic layer control, and anisotropic etching procedures that allows for the precise sculpturing of device features even in the limit of extreme aspect ratios. However, upcoming application needs puts requirements on optimized designs or device performances, e.g. in terms of integration density, power efficiency, modulation bandwidth or spectral response, which call for innovative and refined methodologies. In the present thesis, we investigate a few different device designs or processing schemes that aims for extended performances or manufacturability as compared to presently available technologies. In specific, we study the design and fabrication of transistor-vertical-cavity surface-emitting lasers (T-VCSELs), the regrowth of InP-based driver electronics in the trenches of arrayed spatial light modulators (SLMs), the epitaxial growth and analysis of quantum dot (QD)-based interband photodetectors, the realization of InGaAs/GaAs QD-based single-photon emitters for the 1.55-μm waveband, as well as the fabrication of discrete and silicon-integrated photonic-crystal surface-emitting lasers (PCSELs). The transistor laser, invented at the University of Illinois around 2006, has received considerable interest due to potential major advantages in modulation bandwidth, noise properties and novel functionality as compared to conventional diode lasers. Here we study the design and fabrication of pnp-type 980-nm AlGaAs/InGaAs/GaAs T-VCSELs. Using an epitaxial regrowth process, an intracavity contacting scheme, and an optimized layer design, continuous-wave (CW) result in terms of threshold, output power and temperature performance comparable to conventional VCSELs could be demonstrated. In addition, the collector-current breakdown mechanism was shown to be due to a band-filling effect rather than an intracavity photon absorption process as previously suggested. A subsequent study regards the epitaxial regrowth for the integration of driver electronics with two-dimensional arrays of spatial light modulators (SLMs). The challenge here relies in controlling the regrowth morphology in the restricted areas that limit the SLM array fill factor. It is shown that the orientation of the SLM array with respect to the crystallographic directions is critical for controlling the regrowth 7 morphology, with mesa alignments along the <001> directions preferable over the <011> directions. Following this scheme, an optimized etch/regrowth process for top-contacted field-effect transistors is demonstrated. Next, we discuss the development of long-wavelength infrared (LWIR; 8-12 μm) detector elements for thermal imaging. Such detectors have traditionally been realized in the mercury-cadmium-telluride system (MCT; high performance but difficult materials properties resulting in high cost) or using AlGaAs/GaAs quantum-well infrared photodetectors (QWIPs; excellent manufacturing properties but compromised performance figures). In this work we consider interband QD photodetectors based on spatially indirect transitions in the In(Ga)Sb QD/InAs type-II system to combine the respective advantages of MCT detectors and QWIPs. An epitaxial growth process is optimized for photo-response in the LWIR regime, and the QD properties were also studied using excitation power-dependent PL and spatially resolved current-voltage spectroscopy using a scanning-tunneling microscope. Quantum dot-based structures were also studied for the development of single-photon telecommunication-wavelength emitters. In this case, InAs QDs were formed in an In-rich InGaAs metamorphic buffer layer grown on GaAs substrate. This resulted in narrow and bright micro-photoluminescence emission lines from isolated QDs around 1.55 μm at low temperature, thereby making the application of such QDs an interesting alternative approach to InAs/InP QDs for the realization of single-photon emitters for telecommunication-wavelength fiber-based quantum networks. Finally, we describe the development of silicon-integrated and discrete photonic-crystal surface-emitting lasers (PCSELs). In the former case, a transfer-print process is used to combine an SOI-based PC structure with an InP-based active region. This results in an ultra-shallow device structure and a buried tunnel-junction configuration is used for current injection. In the latter case, the metal-organic vapor-phase epitaxy (MOVPE) growth conditions are tuned to form perfectly encapsulated cavities in the InP matrix. Low-threshold lasing is thereby obtained from optical pumping.