We investigate α-(AlxGa1-x)2O3 layers deposited by PLD for 0≤x≤1 on a- and m-plane sapphire. RSM measurements reveal a fundamental difference for these planes. Pseudomorphic α-(AlxGa1-x)2O3 on m-plane sapphire shows a shear strain e'5 along the c-axis vanishing on a-plane sapphire. Similarly, only relaxed m-plane α-(AlxGa1-x)2O3 exhibits a global lattice tilt in c-axis direction. Modeling of lattice constants and e'5 as function of x prove the shear strain to be due to the non-vanishing C14 component of the stress-strain tensor for α-(AlxGa1-x)2O3 contributing only for the m-plane. We further explain the occurrence of the lattice tilt and identify possible relaxation mechanisms.
Combination of monolayer (ML) transition metal dichalcogenides (TMDC) with molecular layers with strong light matter coupling can enhance, control, and spectrally tune the absorption and emission of such heterostructures. Essential is hereby the energy level alignment at the heterointerface that governs the transfer of electronic excitations. At interfaces with a staggered type-II energy level alignment fast excited-state charge transfer has been utilized to enhance and spectrally expand the photoresponse of MoS2-based hybrid photodetectors. At interfaces with a straddling type-I energy level alignment, transfer of excitons on a sub-picosecond time scale results in an enhanced PL yield from ML-MoS2 in the heterostructure and an according overall modulation of the photo-response.
Molecular electrical doping is of central technological relevance for organic (opto-) electronics since it allows control of charge carrier density and Fermi level position in organic semiconductors (OSCs). Here, we chose to investigate the doping capability of the n-dopant 1,2,3,4,1′,2′,3′,4′-octaphenylrhodocene (OPR). Using the bulky, strongly reducing metallocene to dope the electron-transport polymer poly{[N,N-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5’-(2,2’-bithiophene)} [P(NDI2OD-T2)] leads to an increased bulk conductivity and decreased contact resistance. While the former is due to low-level n-doping of the polymer, trap filling and concomitant charge carrier mobility increase, the latter is caused by an accumulation of OPR at an indium tin oxide (ITO) substrate.
In this work we investigate the mechanisms responsible for the energy level alignment at inorganic and organic semiconductors interfaces with photoelectron spectroscopy. We focus on the different contributions that lead to a substantial work function increase (up to 2.5 eV) when depositing thin layers of organic acceptor molecules [1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile (HATCN) and 2,2'-(perfluoronaphthalene-2,6- diylidene)dimalononitrile (F6-TCNNQ)] on two different inorganic semiconductors (ZnO and GaN). We discuss models to describe this work function increase, which take into account the role of bulk donor concentration of the inorganic semiconductors, their surface state density, and the distance between the inorganic semiconductor and the adsorbed molecules, and we emphasize the importance of surface states on the inorganic semiconductor. The absence of any adsorption-induced core level features for F6-TCNNQ indicates fractional charge transfer, in contrast to HATCN, where additional core level features indicate integer charge transfer. Finally, we demonstrate the utility of this interlayer approach by changing the energy level alignment between the showcase hybrid system ZnO/Sp6
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