Monolithic Integration of Diluted-Nitride III–V-N Compounds on Silicon Substrates: Toward the III–V/Si Concentrated Photovoltaics

Abstract

GaAsPN semiconductors are promising material for the development of high-efficiency tandem solar cells on silicon substrates. GaAsPN diluted-nitride alloy is studied as the top-junction material due to its perfect lattice matching with the Si substrate and its ideal bandgap energy allowing a perfect current matching with the Si bottom cell. The GaP/Si interface is also studied in order to obtain defect-free GaP/Si pseudo-substrates suitable for the subsequent GaAsPN top junctions growth. Result shows that a double-step growth procedure suppresses most of the microtwins and a bi-stepped Si buffer can be grown, suitable to reduce the anti-phase domains density. We also review our recent progress in materials development of the GaAsPN alloy and our recent studies of all the different building blocks toward the development of a PIN solar cell. GaAsPN alloy with energy bandgap around 1.8 eV, lattice matched with the Si substrate, has been achieved. This alloy displays efficient photoluminescence at room temperature and good light absorption. An earlystage GaAsPN PIN solar cell prototype has been grown on a GaP(001) substrate. The external quantum efficiency and the I-V curve show that carriers have been extracted from the GaAsPN alloy absorber, with an open-circuit voltage above 1 eV, however a low short-circuit current density obtained suggests that GaAsPN structural properties need further optimization. Considering all the pathways for improvement, the 2.25% efficiency and IQE around 35% obtained under AM1.5G is however promising, therefore validating our approach for obtaining a lattice-matched dual-junction solar cell on silicon substrate.

Optical absorption and thermal conductivity of GaAsPN absorbers grown on GaP in view of their use in multijunction solar cells

“…With respect to tandem solar cell applications on silicon, the sample with a 10% As content is the most interesting as it guarantees both perfect lattice-matching and an absorption edge in the targeted [1.7-1.8 eV] range of energy [11]. With this configuration, a GaAsPN/Si tandem solar cell would theoretically reach 37% efficiency under AM 1.5G of solar radiation [8].…”

“…GaAsPN alloys which are grown either by molecular beam epitaxy (MBE) or metalorganic vapor phase epitaxy (MOVPE) are very attractive materials for multijunction solar cells [5][6][7][8]. This is due to the high radiative efficiency and the possibility of lattice matching with GaP [4], and more particularly with Si substrates [5,6].…”

Multijunction photovoltavics: integrating III–V semiconductor heterostructures on silicon

“…This cell exhibited a remarkable fill factor (the ratio of the maximum obtainable power and the product of the open-circuit voltage and short-circuit current) of 71%. 7 The short-circuit current was 3.77mA/cm 2 but the opencircuit voltage was relatively low at 0.89V. Assuming that a 1 m thick GaAsPN layer is necessary to absorb the main part of the solar spectrum and, considering the absence of any antireflective coating, the sample with a thinner (300nm) absorber displayed a short-circuit current density close to its theoretical maximum at 1 sun of roughly 5mA/cm 2 .…”

A growth diagram for chemical beam epitaxy of GaP1−xNx alloys on nominally (001)-oriented GaP-on-Si substrates

“…The incorporation of small amounts of N into GaP, besides decreasing the lattice parameter, induces an indirectto-direct band gap transition well described by the band anticrossing model [1,2]. Remarkably, for a N mole fraction = 0.021, the ternary compound GaP 1− N is latticematched to Si with a direct band gap of about 1.96 eV at room temperature, making this material rather unique for the monolithic integration of pseudomorphic red-light emitters and III-V photovoltaic solar cells with the widespread, highly scalable and cost-effective Si technology [3,4,5,6,7,8,9,10]. Nevertheless, despite of the great potential of this compound, commercial red-light emitting devices are still based on Al In Ga 1− − P alloys [11] and the efficiency of GaP 1− N on Si photovoltaic solar cells remains too low as to consider this material combination a competitive technology [8].…”