We present an experimental setup capable of time resolved photoluminescence spectroscopy for photon energies in the range of0.51 to 0.56 eV with an instrument time response of75 ps.The detection system is based on opt...We present an experimental setup capable of time resolved photoluminescence spectroscopy for photon energies in the range of0.51 to 0.56 eV with an instrument time response of75 ps.The detection system is based on optical parametric three wave mixing,operates at room temperature,has spectral resolving power,and is shown to be well suited for investigating dynamical processes in germanium-tin alloys.In particular,the carrier lifetime ofa direct-bandgap Ge1-xSnx film with concentration x=12.5%and biaxial strain-0.55%is determined to be 217±15 ps at a temperature of 20 K.A room-temperature investigation indicates that the variation in this life-time with temperature is very modest.The characteristics of the photoluminescence as a function of pump fuence are discussed.展开更多
Vapor transport growth of atomically thin MoS2 layers on patterned substrates is investigated, as it is a step towards the self-aligned growth and formation of heterojunctions, which could be useful in future applicat...Vapor transport growth of atomically thin MoS2 layers on patterned substrates is investigated, as it is a step towards the self-aligned growth and formation of heterojunctions, which could be useful in future applications. Enhanced formation of MoS2 flakes at the pattern edges is observed on both the substrates examined, namely, patterned thermal SiO2 on Si（100） and graphene flakes on SiO2. The diffusion driven growth leads to the formation of MoS2 monolayers （MLs） with sizes of tens of micrometers around the edges of SiO2 patterns. The growth mode and the optical quality of the MoS2 flakes can be controlled by varying the substrate temperature. Besides the lateral growth, 3R-type pyramids are obtained on prolonging the growth. Lateral MoS2-graphene heterostructures are obtained by using graphene flakes on SiO2 as a substrate.展开更多
We present comprehensive modeling of a Si GeSn multi-quantum well laser that has been previously experimentally shown to feature an order of magnitude reduction in the optical pump threshold compared to bulk lasers.We...We present comprehensive modeling of a Si GeSn multi-quantum well laser that has been previously experimentally shown to feature an order of magnitude reduction in the optical pump threshold compared to bulk lasers.We combine experimental material data obtained over the last few years with k·p theory to adapt transport,optical gain,and optical loss models to this material system (drift-diffusion,thermionic emission,gain calculations,free carrier absorption,and intervalence band absorption). Good consistency is obtained with experimental data,and the main mechanisms limiting the laser performance are discussed. In particular,modeling results indicate a low non-radiative lifetime,in the 100 ps range for the investigated material stack,and lower than expectedΓ-L energy separation and/or carrier confinement to play a dominant role in the device properties. Moreover,they further indicate that this laser emits in transverse magnetic polarization at higher temperatures due to lower intervalence band absorption losses. To the best of our knowledge,this is the first comprehensive modeling of experimentally realized Si GeSn lasers,taking the wealth of experimental material data accumulated over the past years into account. The methods described in this paper pave the way to predictive modeling of new (Si)GeSn laser device concepts.展开更多
文摘We present an experimental setup capable of time resolved photoluminescence spectroscopy for photon energies in the range of0.51 to 0.56 eV with an instrument time response of75 ps.The detection system is based on optical parametric three wave mixing,operates at room temperature,has spectral resolving power,and is shown to be well suited for investigating dynamical processes in germanium-tin alloys.In particular,the carrier lifetime ofa direct-bandgap Ge1-xSnx film with concentration x=12.5%and biaxial strain-0.55%is determined to be 217±15 ps at a temperature of 20 K.A room-temperature investigation indicates that the variation in this life-time with temperature is very modest.The characteristics of the photoluminescence as a function of pump fuence are discussed.
文摘Vapor transport growth of atomically thin MoS2 layers on patterned substrates is investigated, as it is a step towards the self-aligned growth and formation of heterojunctions, which could be useful in future applications. Enhanced formation of MoS2 flakes at the pattern edges is observed on both the substrates examined, namely, patterned thermal SiO2 on Si（100） and graphene flakes on SiO2. The diffusion driven growth leads to the formation of MoS2 monolayers （MLs） with sizes of tens of micrometers around the edges of SiO2 patterns. The growth mode and the optical quality of the MoS2 flakes can be controlled by varying the substrate temperature. Besides the lateral growth, 3R-type pyramids are obtained on prolonging the growth. Lateral MoS2-graphene heterostructures are obtained by using graphene flakes on SiO2 as a substrate.
文摘We present comprehensive modeling of a Si GeSn multi-quantum well laser that has been previously experimentally shown to feature an order of magnitude reduction in the optical pump threshold compared to bulk lasers.We combine experimental material data obtained over the last few years with k·p theory to adapt transport,optical gain,and optical loss models to this material system (drift-diffusion,thermionic emission,gain calculations,free carrier absorption,and intervalence band absorption). Good consistency is obtained with experimental data,and the main mechanisms limiting the laser performance are discussed. In particular,modeling results indicate a low non-radiative lifetime,in the 100 ps range for the investigated material stack,and lower than expectedΓ-L energy separation and/or carrier confinement to play a dominant role in the device properties. Moreover,they further indicate that this laser emits in transverse magnetic polarization at higher temperatures due to lower intervalence band absorption losses. To the best of our knowledge,this is the first comprehensive modeling of experimentally realized Si GeSn lasers,taking the wealth of experimental material data accumulated over the past years into account. The methods described in this paper pave the way to predictive modeling of new (Si)GeSn laser device concepts.
