We exposed a series of AlGaAs/GaAs double heterostructure test articles grown by molecular beam epitaxy and metalorganic chemical vapor deposition to electron radiation. The active regions of the test articles were doped p-type, n-type, or unintentionally. Above bandgap steady state and time-resolved photoluminescence spectroscopy were used to characterize radiation-induced changes in the band structure and carrier dynamics of the test articles. The effects of 1 MeV electron radiation on the low temperature steady state photoluminescence and room temperature carrier lifetime varied with dopant type and concentration. The doping dependence of the lifetime damage coefficient indicates that dopants can mitigate the impact of radiation-induced non-radiative carrier recombination processes.
Photoluminescence measurements on a series of GaAs double heterostructures demonstrate a rapid quenching of carriers in the GaAs layer at irradiance levels below 0.1 W/cm2 in samples with a GaAs-on-InGaP interface. These results indicate the existence of non-radiative defect centers at or near the GaAs-on-InGaP interface, consistent with previous reports showing the intermixing of In and P when free As impinges on the InGaP surface during growth. At low irradiance, these defect centers can lead to sub-ns carrier lifetimes. The defect centers involved in the rapid carrier quenching can be saturated at higher irradiance levels and allow carrier lifetimes to reach hundreds of nanoseconds. To our knowledge, this is the first report of a nearly three orders of magnitude decrease in carrier lifetime at low irradiance in a simple double heterostructure. Carrier quenching occurs at irradiance levels near the integrated Air Mass Zero (AM0) and Air Mass 1.5 (AM1.5) solar irradiance. Additionally, a lower energy photoluminescence band is observed both at room and cryogenic temperatures. The temperature and time dependence of the lower energy luminescence is consistent with the presence of an unintentional InGaAs or InGaAsP quantum well that forms due to compositional mixing at the GaAs-on-InGaP interface. Our results are of general interest to the photovoltaic community as InGaP is commonly used as a window layer in GaAs based solar cells.
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