No abstract

growth reactions from continuing toward bulk metal chalcogenides by kinetic stabilization. [1] In most cases, phosphine ligands were used for this purpose, [2] sometimes being supported by additional organic substituents on the chalcogen atoms. [3] Ternary clusters have also been reported that include a second type of metal atoms, [4] which enables tuning of structural and physical features within the range of the respective binary compounds. [5] Diversity can be further enhanced by attachment of functional organic ligands to the metal atoms of the clusters for tailoring material properties for optoelectronics or solar cells. [6] Recently, our group has reported on the outstanding nonlinear optical properties of adamantane-type clusters with the general composition [(RT) 4 S 6 ] (R = organic substituent; T = Si, Ge, Sn). [7] We found that amorphous compounds with aromatic ligands transform infrared laser light into highly directional white light, while crystalline compounds or those with aliphatic ligands show strong second harmonic generation. Yet, the prerequisites for white-light generation are still under debate, and it is not clear whether the strong optical nonlinearities are an inherent molecular property or have their origin in the cluster habitus.To shed light onto this physical scenario, we combined the adamantane-type clusters with metal complexes. [8] This allowed In order to gain more information on the white-light generation by amorphous molecular materials, the influence of metal complex substituents on the photophysical properties of potential white-light emitters is investigated. Three compounds of the general type [{(R 3 P) 3 MSn}{PhSn} 3 S 6 )], with R/M = Me/Au (1), Et/Ag (4), and Me/Cu (5), are produced by reactions of the organotin sulfide cluster [(PhSn) 4 S 6 ] (A) with the corresponding coinage metal complexes [M(PR 3 ) 3 Cl]. Excess of the gold complex in the reaction leads to rearrangement and formation of [Au(PMe 3 ) 4 ][Au(PMe 3 ) 2 ][(PhSnCl) 3 S 4 ] (2). The use of PMe 3 instead of PEt 3 in the reaction with the silver salt causes decomposition and affords [(Me 3 P) 3 AgSnCl 3 ](3). All compounds are structurally characterized, and the necessity of sterically stabilizing PEt 3 groups at the silver complex in 4 are rationalized by density functional theory (DFT) calculations. Measurements of the photophysical properties of 1, 4, and 5 show that the introduction of the metallo-ligands indeed affects the materials properties, and at the same time confirm that the reduction of the molecular symmetry alone is not a sufficient condition for white-light generation (WLG), which still requires amorphicity of the compound. This is realized for 1 and 4 in situ, while reabsorption processes inhibit WLG in case of the copper compound 5.

Cubic nitrides are candidate materials for next-generation optoelectronic applications as they possess no internal fields and promise to cover large parts of the electromagnetic spectrum from the deep UV toward the mid-infrared. Their successful application demands high-quality epitaxial growth of c-GaN as a base material. This infers a virtually perfect crystallinity as well as smooth surfaces and interfaces despite the limited availability of suitable substrate materials. Here, we systematically introduce pre-growth treatments and c-AlN buffer layers to optimize c-GaN epitaxial layers. Optimized growth parameters yield extremely small surface roughness values below 1 nm root mean square of phase pure c-GaN layers with very limited stacking fault densities as highlighted by scanning transmission electron microscopy. The crystallinity is monitored by X-ray diffraction and surpasses the current standards. We study the effects of the pre-growth procedures on the optical response by photoluminescence spectroscopy and reconfirm the high structural quality of the epitaxial layers. The combined optimization of all layer properties through the universally applicable approach allows for the growth of more complex quantum structures toward device applications.

The ongoing miniaturization of semiconductor devices renders charge‐carrier transport along interfaces increasingly important. The characteristic length scales in state‐of‐the‐art semiconductor technology span only a few nanometers. Consequently, charge‐carrier transport inevitably occurs directly at interfaces between adjacent layers rather than being confined to a single material. Herein, charge‐carrier diffusion is systematically studied in prototypical active layer systems, namely, in type‐I direct‐gap quantum wells and in type‐II heterostructures. The impact of internal interfaces are revealed in detail as charge‐carrier diffusion takes place much closer to or even across the internal interfaces in type‐II heterostructures. Type‐I quantum wells and type‐II heterostructures exhibit comparable diffusion rates given similar inhomogeneous exciton linewidths. Consequently, the changes in the structural quality of the interfaces are responsible for changes in diffusion and charge‐carrier transport along interfaces rather than the existence of the interfaces themselves.

Cubic nitrides are candidate materials for next-generation optoelectronic applications as they lack internal fields and promise to cover large parts of the electromagnetic spectrum from the deep UV towards the mid infrared. This demands high-quality epitaxial growth of c-GaN as base material. We demonstrate the influence of pre-growth treatments and c- AlN buffer layers on the quality of c-GaN grown on 3C-SiC/Si substrates by molecular beam epitaxy (MBE). Optimized parameters yield extremely small surface roughness values below 1 nm of phase pure c-GaN layers with very limited stacking fault densities. Structural properties have been studied by X-ray diffraction and atomic force microscopy and surpasses the current standards, which allows for growth of more complex quantum structures for device application.