Increasing the quantum efficiency of InAs/GaAs QD arrays for solar cells grown by MOVPE without using strain‐balance technology

Abstract

Research into the formation of InAs quantum dots (QDs) in GaAs using the metalorganic vapor phase epitaxy technique is presented. This technique is deemed to be cheaper than the more often used and studied molecular beam epitaxy. The best conditions for obtaining a high photoluminescence response, indicating a good material quality, have been found among a wide range of possibilities. Solar cells with an excellent quantum efficiency have been obtained, with a sub-bandgap photo-response of 0.07 mA/cm per QD layer, the highest achieved so far with the InAs/GaAs system, proving the potential of this technology to be able to increase the efficiency of lattice-matched multi-junction solar cells and contributing to a better understanding of QD technology toward the achievement of practical intermediate-band solar cells.

The investigation of InGaAs quantum dot growth peculiarities for GaAs intermediate band solar cells

“…It can be seen that the deposition of 1 ML InGaAs is not enough to start the formation of coherent islands since the obtained spectrum has a shape close to the quantum well one with two apparent peaks: 870 nm from the GaAs matrix and 900 nm from the wetting layer of the QD. The resulting optimum thickness of 2 ML exceeds the critical thickness for the formation of InAs QDs on the GaAs surface, which is 1.7 ML like it has been shown in [8]. In fact, In 0.8 Ga 0.2 As has a smaller difference in the parameters of the crystal lattices with GaAs so when the QD growth in the Stranski-Krastanov mode the more material is required to begin the formation of the islands.…”

“…Currently, QDs widely used in active area of lasers and allow increasing the radiation wavelength, improving thermal stability and reducing the threshold current, compared with traditional devices. However, first successful results of the application QDs in photovoltaic began publishing only recently and demonstrate the expansion of spectral sensitivity of the SC via photoelectric effect in InAs/GaAs QD [6][7][8]. In these works a noticeable but small contribution of QDs to the internal quantum efficiency of single-junction SC has been obtained.…”

“…1b) the absorption was increased due to 1, 5, 10 and 20 layers of QDs grown through the GaAs spacers with a thickness 35 nm. The spacers grew at elevated temperature 600°C which was also necessary for preparing a planar surface for each subsequent layer of QD [8]. These structures were designed to investigate the possibility of embedding several layers of QDs into the active region of GaAs SC.…”

“…The amount of InGaAs material was varied from 1 to 4 monolayers (ML). The thickness of GaAs cap layer was chosen based on the known lateral sizes of QDs [7,8] and was 5 nm for all experimental structures. Nevertheless, an additional experiment was performed to evaluate the effect of this parameter on the PL spectrum in which the thickness of GaAs cap layer was 7 nm with the amount of InGaAs material of 2 ML.…”

Квантовые точки InAs, выращенные в метаморфной матрице In-=SUB=-0.25-=/SUB=-Ga-=SUB=-0.75-=/SUB=-As методом МОС-гидридной эпитаксии

“…Метаморфные КТ также были использованы для создания источников одиночных фотонов [9][10]. Кроме того, InAs КТ также весьма перспективны для улучшения характеристик фотопреобразователей раз-личного спектрального диапазона [11,12].…”