The defect properties of InGaAsN dilute nitrides grown as sub-monolayer digital alloys (SDAs) by molecular beam epitaxy for photovoltaic application were studied by space charge capacitance spectroscopy. Alloys of i-InGaAsN (Eg = 1.03 eV) were lattice-matched grown on GaAs wafers as a superlattice of InAs/GaAsN with one monolayer of InAs (<0.5 nm) between wide GaAsN (7–12 nm) layers as active layers in single-junction solar cells. Low p-type background doping was demonstrated at room temperature in samples with InGaAsN layers 900 nm and 1200 nm thick (less 1 × 1015 cm−3). According to admittance spectroscopy and deep-level transient spectroscopy measurements, the SDA approach leads to defect-free growth up to a thickness of 900 nm. An increase in thickness to 1200 nm leads to the formation of non-radiative recombination centers with an activation energy of 0.5 eV (NT = 8.4 × 1014 cm−3) and a shallow defect level at 0.20 eV. The last one leads to the appearance of additional doping, but its concentration is low (NT = 5 × 1014 cm−3) so it does not affect the photoelectric properties. However, further increase in thickness to 1600 nm, leads to significant growth of its concentration to (3–5) × 1015 cm−3, while the concentration of deep levels becomes 1.3 × 1015 cm−3. Therefore, additional free charge carriers appearing due to ionization of the shallow level change the band diagram from p-i-n to p-n junction at room temperature. It leads to a drop of the external quantum efficiency due to the effect of pulling electric field decrease in the p-n junction and an increased number of non-radiative recombination centers that negatively impact lifetimes in InGaAsN.
Defect properties of InGaAsN layers grown as sub-monolayer digital alloys by molecular beam epitaxy
Artem I. Baranov, Alexander S. Gudovskikh, Dmitry A. Kudryashov, Alexandra A. Lazarenko, Ivan A. Morozov, Alexey M. Mozharov, Ekaterina V. Nikitina, Evgeny V. Pirogov, Maxim S. Sobolev, Kirill S. Zelentsov, Anton Yu. Egorov, Arouna Darga, Sylvain Le Gall, Jean-Paul Kleider; Defect properties of InGaAsN layers grown as sub-monolayer digital alloys by molecular beam epitaxy. J. Appl. Phys. 28 April 2018; 123 (16): 161418. https://doi.org/10.1063/1.5011371
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