The ancient emission formulas of Langmuir and Richardson entered the calculations of subtle effects in semiconductor devices as basic ones.But,in the physics of semiconductor devices,these models have long played a pu...The ancient emission formulas of Langmuir and Richardson entered the calculations of subtle effects in semiconductor devices as basic ones.But,in the physics of semiconductor devices,these models have long played a purely decorative role,since they can describe in the most rough approximation only individual sections of the I-V characteristic.But it is precisely the fact that these formulas are basic when describing the barrier current-voltage characteristics(CVC)and prevented the consideration and use of thermoelectric effects in materials on a nano-scale.Thus,as these basic emission models actually imposed a ban on the MEASURABILITY of local thermoelectric effects,the existence of which has already been proven both phenomenologically and experimentally.The quantum transition technique is based on classical models.But it can also be used to correct these classic formulas.The calculation of the spatial transition of electrons over the potential barrier,taking into account the polarity of the kinetic energy,gives currents that are significantly higher than the currents of Langmuir and Richardson,including in the initial section of the I-V characteristic.Moreover,ballistic currents are concentrated at energy levels close to the threshold.This effect of condensation of electrons flowing down the barrier transforms the"anomalous"Seebeck coefficients into normal MEASURABLE Local Thermal EMF,including in p-n junctions.展开更多
GaAs-based microdisk lasers with an active region representing a dense array of indium-rich islands(InGaAs quantum well-dots) were studied using direct small-signal modulation. We demonstrate that using dense arrays o...GaAs-based microdisk lasers with an active region representing a dense array of indium-rich islands(InGaAs quantum well-dots) were studied using direct small-signal modulation. We demonstrate that using dense arrays of InGaAs quantum well-dots enables uncooled high-frequency applications with a GHz-range bandwidth for microdisk lasers. A maximum 3 dB modulation frequency of 5.9 GHz was found in the microdisk with a radius of 13.5 μm operating without a heatsink for cooling. A modulation current efficiency factor of 1.5 GHz∕mA1∕2 was estimated.展开更多
Colloidal semiconductor quantum dots(QDs)constitute a perfect material for ink-jet printable large area displays,photovoltaics,light-emitting diode,bio-imaging luminescent markers and many other applications.For this ...Colloidal semiconductor quantum dots(QDs)constitute a perfect material for ink-jet printable large area displays,photovoltaics,light-emitting diode,bio-imaging luminescent markers and many other applications.For this purpose,efficient light emission/absorption and spectral tunability are necessary conditions.These are currently fulfilled by the direct bandgap materials.Si-QDs could offer the solution to major hurdles posed by these materials,namely,toxicity(e.g.,Cd-,Pb-or As-based QDs),scarcity(e.g.,QD with In,Se,Te)and/or instability.Here we show that by combining quantum confinement with dedicated surface engineering,the biggest drawback of Si—the indirect bandgap nature—can be overcome,and a‘direct bandgap’variety of Si-QDs is created.We demonstrate this transformation on chemically synthesized Si-QDs using state-of-the-art optical spectroscopy and theoretical modelling.The carbon surface termination gives rise to drastic modification in electron and hole wavefunctions and radiative transitions between the lowest excited states of electron and hole attain‘direct bandgap-like’(phonon-less)character.This results in efficient fast emission,tunable within the visible spectral range by QD size.These findings are fully justified within a tight-binding theoretical model.When the C surface termination is replaced by oxygen,the emission is converted into the well-known red luminescence,with microsecond decay and limited spectral tunability.In that way,the‘direct bandgap’Si-QDs convert into the‘traditional’indirect bandgap form,thoroughly investigated in the past.展开更多
文摘The ancient emission formulas of Langmuir and Richardson entered the calculations of subtle effects in semiconductor devices as basic ones.But,in the physics of semiconductor devices,these models have long played a purely decorative role,since they can describe in the most rough approximation only individual sections of the I-V characteristic.But it is precisely the fact that these formulas are basic when describing the barrier current-voltage characteristics(CVC)and prevented the consideration and use of thermoelectric effects in materials on a nano-scale.Thus,as these basic emission models actually imposed a ban on the MEASURABILITY of local thermoelectric effects,the existence of which has already been proven both phenomenologically and experimentally.The quantum transition technique is based on classical models.But it can also be used to correct these classic formulas.The calculation of the spatial transition of electrons over the potential barrier,taking into account the polarity of the kinetic energy,gives currents that are significantly higher than the currents of Langmuir and Richardson,including in the initial section of the I-V characteristic.Moreover,ballistic currents are concentrated at energy levels close to the threshold.This effect of condensation of electrons flowing down the barrier transforms the"anomalous"Seebeck coefficients into normal MEASURABLE Local Thermal EMF,including in p-n junctions.
文摘GaAs-based microdisk lasers with an active region representing a dense array of indium-rich islands(InGaAs quantum well-dots) were studied using direct small-signal modulation. We demonstrate that using dense arrays of InGaAs quantum well-dots enables uncooled high-frequency applications with a GHz-range bandwidth for microdisk lasers. A maximum 3 dB modulation frequency of 5.9 GHz was found in the microdisk with a radius of 13.5 μm operating without a heatsink for cooling. A modulation current efficiency factor of 1.5 GHz∕mA1∕2 was estimated.
基金This work was financially supported by Stichting der Fundamenteel Onderzoek der Materie and Stichting voor de Technische Wetenschappen.Part of this work(CPU,JMJP andHZ)was financed by the Dutch Polymer Institute for funding of UCin Functional Polymer Systemsproject no.681,and(ANP andAAP)Russian Foundation for Basic Research and‘Dynasty’-Foundation of International Center for Fundamental Physics in Moscow.
文摘Colloidal semiconductor quantum dots(QDs)constitute a perfect material for ink-jet printable large area displays,photovoltaics,light-emitting diode,bio-imaging luminescent markers and many other applications.For this purpose,efficient light emission/absorption and spectral tunability are necessary conditions.These are currently fulfilled by the direct bandgap materials.Si-QDs could offer the solution to major hurdles posed by these materials,namely,toxicity(e.g.,Cd-,Pb-or As-based QDs),scarcity(e.g.,QD with In,Se,Te)and/or instability.Here we show that by combining quantum confinement with dedicated surface engineering,the biggest drawback of Si—the indirect bandgap nature—can be overcome,and a‘direct bandgap’variety of Si-QDs is created.We demonstrate this transformation on chemically synthesized Si-QDs using state-of-the-art optical spectroscopy and theoretical modelling.The carbon surface termination gives rise to drastic modification in electron and hole wavefunctions and radiative transitions between the lowest excited states of electron and hole attain‘direct bandgap-like’(phonon-less)character.This results in efficient fast emission,tunable within the visible spectral range by QD size.These findings are fully justified within a tight-binding theoretical model.When the C surface termination is replaced by oxygen,the emission is converted into the well-known red luminescence,with microsecond decay and limited spectral tunability.In that way,the‘direct bandgap’Si-QDs convert into the‘traditional’indirect bandgap form,thoroughly investigated in the past.
