InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells

Abstract

Quantum wires (QWRs) form naturally when growing strain balanced InGaAs/GaAsP multi-quantum wells (MQW) on GaAs [100] 6° misoriented substrates under the usual growth conditions. The presence of wires instead of wells could have several unexpected consequences for the performance of the MQW solar cells, both positive and negative, that need to be assessed to achieve high conversion efficiencies. In this letter, we study QWR properties from the point of view of their performance as solar cells by means of transmission electron microscopy, time resolved photoluminescence and external quantum efficiency (EQE) using polarised light. We find that these QWRs have longer lifetimes than nominally identical QWs grown on exact [100] GaAs substrates, of up to 1 μs, at any level of illumination. We attribute this effect to an asymmetric carrier escape from the nanostructures leading to a strong 1D-photo-charging, keeping electrons confined along the wire and holes in the barriers. In principle, these extended lifetimes could be exploited to enhance carrier collection and reduce dark current losses. Light absorption by these QWRs is 1.6 times weaker than QWs, as revealed by EQE measurements, which emphasises the need for more layers of nanostructures or the use light trapping techniques. Contrary to what we expected, QWR show very low absorption anisotropy, only 3.5%, which was the main drawback a priori of this nanostructure. We attribute this to a reduced lateral confinement inside the wires. These results encourage further study and optimization of QWRs for high efficiency solar cells.

Impact of in-situ annealing on dilute-bismide materials and its application to photovoltaics

“…For the current device structures, the base region was measured to be p-type with the background concentration as high as − × − 1 2 10 cm 19 3 from the electrochemical capacitance voltage measurement. The second factor can be addressed by strain compensation, employing tensile-strained GaAs 1À y P y barriers [8], which allow for the increased thickness of the base region, as reported in the context of InGaAs/GaAsP MQW solar cells [19][20][21]. For the best extraction of the electron and hole pairs generated in the based region, the GaAsP thickness has to be thin enough with high P fraction so that there is weak electron-hole confinement in the QW, allowing the formation of minibands Intensity (a.u.…”

Рекомбинация в GaAs p-i-n-структурах с InGaAs квантово-размерными объектами: моделирование и закономерности

“…Методом металлоорганической газовой эпитаксии создавались GaAs p−i−n-структуры, в которые вводилось различное число (3,4,5,7,10) In 0.4 Ga 0.6 As квантово-размерных объектов (рядов). Анализировалось влияние числа рядов на зависимость V oc −C (напряжение холостого хода -кратность солнечного излучения), которая после калибровки превращается в V oc −J g -характеристику, эквивалентную искомой безрезистивной темновой ВАХ.…”

“…Эксперименты по внедрению квантовых объектов (точек, ям и других подобных объектов) в p−i−n-структуру проводятся в настоящее время из-за возможности улучшения характеристик полупроводниковых приборов (фотодетекторов, солнечных элементов, лазерных диодов и др. [1][2][3][4][5]).…”

Quantum wire‐on‐well (WoW) cell with long carrier lifetime for efficient carrier transport

“…Recently, it was found that photoluminescence (PL) lifetime for such an undulated InGaAs/GaAsP superlattice exceeds 1 ms owing to asymmetric carrier escape, or photo‐charging , which is not observable for a planar superlattice. Such long lifetime of the carriers trapped in the wires is expected to make carrier collection easier than the case of planer superlattice.…”