Date: Friday, October 07, 2022

Time:  1:30 PM

Location:  PAIS, Room 2540

Committee Members:

Abstract:

The creation of a laser cooled semiconductor device has been a long-sought achievement. GaAs-based devices have emerged as a promising candidate for the realization of this goal. Efforts to improve the efficiency of such devices have enabled the material to exhibit external quantum efficiencies (EQE, a measure of the probability that an excitation leads to the emission of a photon) of 99.5%. Despite this impressive feat, a laser coolable device remains elusive.

To investigate the obstacles to such a device, the material characteristics of GaAs-based double heterostructures (DHS) are theoretically and experimentally examined. Through this study, a GaAs | AlGaAs DHS is shown to achieve an EQE performance equivalent to GaAs | GaInP DHS (the 99.5% EQE device) for the first time. Additionally, this structure exhibits a lower parasitic background absorption (PBA), heat-induced absorption of a pump laser, than that attainable in current GaAs | GaInP DHS. This was enabled by a supporting study into semiconductor growth techniques, specifically metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), finding MBE-grown structures had an order of magnitude smaller PBA than those grown with MOCVD. Furthermore, the PBA contributions for individual layers of these GaAs DHS is reported for the first time using a novel thermal lens technique. The passivation layers are identified as the dominant contributors at 1020-1070 nm, with the GaAs layer the primary contributor at resonant wavelengths.