We studied the growth of GaNAs/AlGaAs heterostructures on GaAs (100) substrates by plasma-assisted molecular beam epitaxy. By introducing periodic growth interruption and nitrogen (N) supply to the interrupted surfaces during the growth of GaNAs, we achieved high controllability of the average N concentration in GaNAs layers. We observed three-dimensional island growth of GaNAs on the N-rich surfaces. The GaNAs island structures exhibit narrow photoluminescence emission at around 1 µm at low temperature, indicating the formation of a large band offset between GaNAs and AlGaAs.
We investigated photoresponses of AlGaAs solar cells in which coupled GaAs quantum wells were embedded in the i-region of p-i-n diodes; we studied how the bias voltage Vb affects the normal photocurrent I generated by the visible light and a “two-step” photocurrent ΔI generated by the absorption of visible and infrared photons. We found that as Vb exceeds −0.2 V, ΔI rises and peaks at 0.6 V, while the normal photocurrent I falls to about half of its saturated level. These findings are discussed in terms of a rate equation model to show that ΔI is mainly determined by the balance of escape and recombination of photogenerated carriers.
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