Recent developments in fabrication of van der Waals heterostructures enable new type of devices assembled by stacking atomically thin layers of two-dimensional materials. Using this approach, we fabricate light-emitting devices based on a monolayer WSe 2 , and also comprising boron nitride tunnelling barriers and graphene electrodes, and observe sharp luminescence spectra from individual defects in WSe 2 under both optical and electrical excitation. This paves the way towards the realization of electrically-pumped quantum emitters in atomically thin semiconductors. In addition we demonstrate tuning by more than 1 meV of the emission energy of the defect luminescence by applying a vertical electric field. This provides an estimate of the permanent electric dipole created by the corresponding electron-hole pair. The light-emitting devices investigated in our work can be assembled on a variety of substrates enabling a route to integration of electrically pumped single quantum emitters with existing technologies in nanophotonics and optoelectronics.The recent observation of direct bandgaps in semiconducting molybdenum and tungsten dichalcogenide monolayers has led to a rise of interest to these two-dimensional (2D) materials and demonstrated their potential for future optoelectronic devices 1,2,3,4 . These one-monolayer-thick crystals are characterised by large exciton binding energies 5,6 and oscillator strengths 7 and can be combined with other layered materials to create heterostructures held together by van der Waals forces 8,9,10,11,12 . This concept has been used to form electrically driven light-emitting structures, where MoX 2 or WX 2 (X=S or Se) monolayers were used as the exciton recombination layers, thin hexagonal boron nitride (hBN) was used for tunnelling barriers and graphene -used for transparent electrodes 11,12 .
We investigate the nonlinear mechanical properties of GaAs nanowires with anisotropic cross-section. Fundamental and second order flexural modes are studied using laser interferometry with good agreement found between experiment and theory describing the nonlinear response under mechanical excitation. In particular, we demonstrate that the sign of the nonlinear coupling between orthogonal modes is dependent on the cross-section aspect ratio. The findings are of interest for applications such as amplitude to frequency conversion and vectorial force sensing.
A monolithic approach to V-band upconverter development has the advantages of lighter weight and lower cost over conventional hybrid approachs for high volume insertions into transmitter systems. This paper will present the design and performance of a complete monolithic upconverter macrocell using 0.2 pm InGaAs/GaAs pseudomorphic HEMT technology. Individual components, including a 2-10 GHz IF amplifier, a V-band upconverting mixer and a Vband amplifier are also described. The measured results demonstrate a conversion gain of 10 dB at V-band by injecting a 2-10 GHz IF frequency with an LO drive of 10 dBm at 54 GHz. This is the first reported monolithic upconverter with good performance and bandwidth at this frequency.
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