Tin-gallium oxide (TGO) epilayers have been characterized through the electron microscopy techniques of wavelength-dispersive X-ray spectroscopy (WDX) and cathodoluminescence. Tin incorporation was found to be highly dependent on growth conditions with (0001)-sapphire and (010)-Ga2O3 substrates enhancing tin incorporation. Cathodoluminescence measurements show that TGO luminescence consists of an enhanced blue emission and quenched UV when compared to Ga2O3.and the onset of new green emission originating from the TGO, further correlated through cross-sectional WDX and cathodoluminescence mapping. As well as luminescence intensity changes TGO films display redshifted luminescence bands associated with a bandgap reduction due to the alloying, confirmed through optical transmission measurements.
Atomic layer deposition (ALD) offers a low thermal budget method for producing α-Ga2O3 films on sapphire substrate. In this paper we review the recent progress on plasma-enhanced ALD growth of α-Ga2O3 and present the optical and photoconductive properties of the deposited films. We show that the deposited material exhibits an epitaxial relationship with the sapphire substrate, and with an atomically sharp film-substrate interface. The α-Ga2O3 films had an optical bandgap energy measured at 5.11 eV, and exhibited a broad luminescence spectrum dominated by ultraviolet, blue and green bands, in line with current literature. We finally demonstrate the suitability of the material for solar-blind photodetection.
We investigated alloy fluctuations at dislocations in III-Nitride alloys (InGaN and AlGaN). We found that in both alloys, atom segregation (In segregation in InGaN and Ga segregation in AlGaN) occurs in the tensile part of dislocations with an edge component. In InGaN, In atom segregation leads to an enhanced formation of In-N chains and atomic condensates which act as carrier localization centers. This feature results in a bright spot at the position of the dislocation in the CL images, suggesting that non-radiative recombination at dislocations is impaired. On the other hand, Ga atom segregation at dislocations in AlGaN does not seem to noticeably affect the intensity recorded by CL at the dislocation. This study sheds light on why InGaN-based devices are more resilient to dislocations than AlGaN-based devices. An interesting approach to hinder non-radiative recombination at dislocations may therefore be to dope AlGaN with In.
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