Recently the AlGaAs and InGaAs samples I've been growing by MOCVD haven't been producing any PL. The AlGaAs samples are bulk and QW structures (AlInGaAs), whereas the InGaAs is the cap/contact layer from a laser structure.
I've ruled out any issue with our PL system as remeasuring older samples gives the same results, and other materials and structures give strong signals - interestingly, InGaAs QWs do produce PL. XRD measurements show no degradation or change in our crystal quality, and the contact resistance of the InGaAs cap layers is also unaffected. I've also ruled out any issues with my Al sources as best I can, and any problems with the reactor by inspecting, cleaning, and changing the chamber furniture.
Our current "best" theory is that we are incorporating some sort of contaminant or defect (possibly vacancies?) from our AsH3 source, which is a couple of years "out of date" (it's a large cylinder and we didn't want to throw away "good" gas). We've attempted to identify possible culprits using SIMS, but there's no trace of any contaminant - of course, they could be at such a low level that they aren't detected efficiently...
Has anyone had a similar experience, or know anything about how an AsH3 degrades or "fails" over time? Or, alternatively, does anyone have any suggestions about an explanation for what we are seeing?
To summarise, recently grown Al(In)GaAs and InGaAs samples do not produce any PL. Whatever the cause is, it does not appear to affect the crystalline quality, composition, contact resistance, or morphology of the samples. SIMS analysis has not identified any source of contamination.
Hi Adam,
Thanks for the interesting post. Two most possible causes for the observation could be the reactor geometry or the As source that resulted in defects. If SIMS and XRD showed that As was present in quantities that it should be, then the parameter to tune could be the reactor geometry. Switching the injection gas lines for the sources and trying to deposit compounds with extreme compositions and high thickness might help identify the issue.
Hi Adam,
Your MOVPE system may have a high content of oxygen that may have contaminated Al-based heterojunction and therefore large defects at the interface leading to luminescence degradation.
Regards
Vijay
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