The compound semiconductor industry is booming and has established its position alongside Si-based integrated microchip industry. For example, LED lights are based on GaN-compounds and communication networks are built on GaAs- and InP-based components.
In his dissertation, Joonas Hilska investigates much less developed GaSb-compound semiconductors. He developed the fabrication process of novel GaSbBi compounds and GaSb quantum dots using molecular beam epitaxy (MBE).
"With MBE, it is possible to create a perfect semiconductor crystal structure one atomic layer at a time", Hilska says.
GaSbBi compounds theoretically promise improved performance of mid-infrared (2-5 µm) laser diodes utilized in precise monitoring of environmental gases or biomarkers. However, the fabrication of GaSbBi compounds is challenging because bismuth (Bi) is difficult to incorporate into GaSb. In the dissertation, Hilska maps-out the growth parameter space suitable for Bi incorporation and utilizes this knowledge to fabricate a laser diode that employs GaSbBi quantum wells of only few nanometers thick.
GaSb quantum dots are fabricated with MBE using a technique called local droplet etching. This enables the ‘drilling’ of nanometer sized holes on semiconductor surfaces.
"When we fill the nanoholes with GaSb, we can create nanostructures with three-dimensional carrier confinement. This creates discrete energy state structure much like in individual atoms, which can be utilized in non-classical light sources that emit only one photon at a time", Hilska says.
In the dissertation, highly uniform GaSb quantum dots are fabricated which are shown to be capable of single-photon emission at 1.5 µm wavelength. This makes the quantum dots suitable for secure quantum encryption applications in existing fiber optic infrastructure.
Public defence on Tuesday 3 December
The doctoral dissertation of MSc Joonas Hilska in the field of semiconductor physics titled Epitaxy of Advanced GaSb-based Semiconductor Light Sources will be publicly examined at the Faculty of Engineering and Natural Sciences at Tampere University on Tuesday 3 December 2024 at 13 o’clock at Hervanta campus, Tietotalo auditorium TB109 (Korkeakoulunkatu 1, Tampere). The opponent will be Professor Mark Hopkinson from the University of Sheffield. The Custos will be Professor Mircea Guina from the Faculty of Engineering and Natural Sciences, Tampere University.