Photoluminescence and charge transfer in the prototypical 2D/3D semiconductor heterostructure MoS2/GaAs

Abstract

The new generation of two-dimensional (2D) materials has shown a broad range of applications for optical and electronic devices. Understanding the properties of these materials when integrated with more traditional three-dimensional (3D) semiconductors is an important challenge for the implementation of ultra-thin electronic devices. Recent observations have shown that by combining MoS 2 with GaAs, it is possible to develop high quality photodetectors and solar cells. Here, we present a study of effects of intrinsic GaAs, p-doped GaAs, and n-doped GaAs substrates on the photoluminescence of monolayer MoS 2 . We observe a decrease in an order of magnitude in the emission intensity of MoS 2 in all MoS 2 /GaAs heterojunctions, when compared to a control sample consisting of a MoS 2 monolayer isolated from GaAs by a few layers of hexagonal boron nitride. We also see a dependence of the trion to A-exciton emission ratio in the photoluminescence spectra on the type of substrates, a dependence that we relate to the static charge exchange between MoS 2 and the substrates when the junction is formed. Scanning Kelvin probe microscopy measurements of heterojunctions suggest type-I band alignments, so that excitons generated on the MoS 2 monolayer will be transferred to the GaAs substrate. Our results shed light on the charge exchange leading to band offsets in 2D/3D heterojunctions, which play a central role in the understanding and further improvement of electronic devices.

Evidence for highly p-type doping and type II band alignment in large scale monolayer WSe2/Se-terminated GaAs heterojunction grown by molecular beam epitaxy

“…5, the final arrangement of the WSe 2 /Se-terminated GaAs(111)B heterojunction exhibits a staggered gap between WSe 2 and GaAs, and qualifies as a type-II band alignment. It is important to note that such band arrangement is not static, as changes in the doping level of GaAs substrate, could shift the alignment to type I, as observed in MoS 2 /GaAs heterostructures fabricated by mechanical transfer, 70 with potential applications in TMD-based optoelectronics. 71…”

Exciton tuning in monolayer WSe2viasubstrate induced electron doping

“…As shown in the intensity map in Fig. 1(c), the PL intensity of WSe 2 on thick hBN is higher than that on thin hBN because of interference enhancement [33,34]. More importantly, comparing the PL intensity of WSe 2 on hBN and HOPG, one can clearly identify that a drastic decrease of PL intensity occurs on HOPG.…”

“…Several mechanisms can cause the low PL quantum yield and thus lead to the decrease of PL intensity, such as the high defect concentration, strong many-body effects, charge dissociation and charge transfer [34][35][36][37] with the literature values [26,41], while the PL peak position of WSe 2 /HOPG shows a marked ∼100 meV redshift, which is much higher than the reported value caused by changing of dielectric environment [18]. Besides the quenching and redshift, the PL line shape changes significantly.…”

“…KPFM is a powerful technique to obtain local surface potential and Fermi level position in the nanoscale [34,53]. We therefore measured KPFM on the WSe 2 /hBN/HOPG hetero-stack to obtain further insight in the energy level alignment at the various interfaces.…”

“…In the ideal case KPFM to be strongly influenced by the measurement environment, tip geometry, parasitic effects such as capacitive coupling, as well as the chosen experimental parameters [54][55][56][57]. Nevertheless, it still qualitatively indicates the trend of Fermi level position and material work functions [34,53,58,59]. The values of the energy levels discussed in the following paragraph are directly extracted from the KPFM measurements.…”