Defect properties of InGaAsN layers grown as sub-monolayer digital alloys by molecular beam epitaxy

Abstract

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 solar cells with layers of GaP based dilute nitrides grown by molecular beam epitaxy

“…A more detailed description of the admittance spectroscopy technique for p-i-n junctions is given in our previous work where fully depleted InGaAsN layers were explored. 35 To estimate parameters of a defect level, the following relation is used:…”

“…Indeed, the latter method was successfully applied to the growth of defect-free InGaAsN (900 nm thick) as InAs/GaAsN in our previous work. 35 The photovoltaic structures are investigated by various capacitive techniques such as capacitance-voltage measurements (C-V), admittance spectroscopy (AS) and DLTS. These experiments provide information on the formation of defects in these compounds during the growth process.…”

Development of 1 eV InGaAsN PIN subcell for MJSC integration and space application

“…Relatively high doping concentration can prevent the space charge region to extend within the whole active layer resulting in lower collection efficiency as it was studied in [11]. Reference [12] also reports that under their growth conditions, 900 nm thick absorber cells are fully depleted whereas 1200 nm thick ones are not.…”

Исследование квантовых ям InP/GaP, полученных методом газофазной эпитаксии

“…Однако ранее было продемонстрировано повышенное формирование центров безызлучательной рекомбинации в таких полупроводниковых слоях из-за встраивания азота в подрешетку фосфора в GaP, что приводило к низким временам жизни неосновных носителей заряда и низкому КПД фотопреобразовательных структур. Тем не менее метод чередующихся квантово-размерных слоев был успешно применен в гетероструктурах InAs/GaAsN для солнечных элементов [4], выращенных методом молекулярно-пучковой эпитаксии на подложках GaAs, а методом атомно-слоевого плазмохимического осаждения были получены сверхрешетки Si/GaP [5]. Таким образом, для солнечной энергетики интересным может являться создание короткопериодных сверхрешеток типа InP/GaP и InP/GaN.…”