Low-temperature photoluminescence of (aluminum) gallium antimonide

Abstract

Low-temperature photoluminescence (LT-PL) is a phenomenon in which a material emits light due to an impinging photonic flux. This concept can be implemented in many ways to investigate the properties of molecular beam epitaxially (MBE) grown semiconductor devices, hence providing an essential tool in the field of optoelectronic research. Moreover, LT-PL can reveal different defects that form in such devices, thus giving insight into the quality of the device and providing crucial information in the optimization of MBE. The cryogenic conditions enhance the ability to identify these defects by narrowing spectral linewidth as well as revealing phonon replicas which would not be observed in modest temperatures. In this thesis, LT-PL was used to analyze different transitions in metamorphically MBE grown bulk (aluminum) gallium antimonide (AlGaSb).

This thesis first covers the phenomena essential for measuring the LT-PL spectra of bulk samples: band structure formation, band gap composition and temperature dependence, excitons, photoluminescence in bulk III-V semiconductors, optical phonons, defects, and recombination mechanisms. From these subjects, theories of defects and phonon replicas rise as the most crucial ones due to their presence in LT-PL.

Four metamorphically on Si-GaAs grown bulk MBE samples with different structures were measured: 1) a GaSb sample, 2) a low-temperature no-capping-layer Al0.3Ga0.7Sb sample, 3) a low-temperature capped Al0.3Ga0.7Sb sample and 4) a high-temperature capped Al0.3Ga0.7Sb sample. The latter three had a distributed bragg reflector to improve the intensity of the LT-PL peaks. The bulks of the samples were grown in different temperatures: First sample bulk was grown at 500°C, second at 395°C, third at 395°C and the fourth at 530°C.

The LT-PL measurements revealed different defect states in bulk (aluminum) gallium antimonide. By comparing the PL peaks with literature, defects states belonging to native defects at around 1.13 eV, phonon replicas at 1.11 eV, oxygen at around 1.00 eV, and GaSb band-to-band transition at 0.850 eV were identified. Moreover, growth temperature increased the intensity of the native defect peak and decreased the intensity of the oxygen peak, proving that the growth temperature has a substantial effect on the LT-PL of AlGaSb devices.