High quality factor dielectric cavities designed to a nanoscale accuracy are mostly used to increase the spontaneous emission rate of a single emitter. Here we show that the coupling, at room temperature, between thick shell CdSe/CdS nanocrystals and random metallic films offers a very promising alternative approach. Optical modes confined at the nanoscale induce strong Purcell factors reaching values as high as 60. Moreover the quantum emission properties can be tailored: strong antibunching or radiative biexcitonic cascades can be obtained with high photon collection efficiency and extremely reduced blinking.
We investigated the nonlinear optical properties of CdSe/CdS nanoplatelets in the vicinity of heavy hole and light hole exciton resonances. The two color pump-probe technique was applied. The first intense pulse created non-equilibrium exciton population, which was detected as a decrease of probe light absorption. We observed intense scattering of excitons between heavy- and light-hole excitonic states. We also studied experimentally saturation of absorption in nanoplatelets. Theoretical description of these phenomena allowed us to determine parameters of exciton dynamics in nanoplatelets.
We investigate the photon statistics of the light emitted by single self-assembled hybrid gold-CdSe/CdS/CdZnS colloidal nanocrystal supraparticles through the detailed analysis of the intensity autocorrelation function $g^{(2)}(τ)$. We first reveal that, despite the large number of nanocrystals involved in the supraparticle emission, antibunching can be observed. We then present a model based on non-coherent Förster energy transfer and Auger recombination that well captures photon antibunching. Finally, we demonstrate that some supraparticles exhibit a bunching effect at short time scales corr…
Large surface to volume ratios of semiconductor nanocrystals cause susceptibility to charge trapping, which can modify luminescence yields and induce single-particle blinking. Optical spectroscopies cannot differentiate between bulk and surface traps in contrast to spin-resonance techniques, which in principle avail chemical information on such trap sites. Magnetic resonance detection via spin-controlled photoluminescence enables the direct observation of interactions between emissive excitons and trapped charges. This approach allows the discrimination of two functionally different trap state…
We report on the synthesis of hybrid light emitting particles with a diameter ranging between 100 and 500 nm, consisting in a compact semiconductor CdSe/CdS/CdZnS nanocrystal aggregate encapsulated by a controlled nanometric size silica and gold layers. We first characterize the Purcell decay rate enhancement corresponding to the addition of the gold nanoshell as a function of the particle size and find a good agreement with the predictions of numerical simulations. Then, we show that the contribution corresponding to Förster resonance energy transfer is inhibited.
Seeded CdSe/CdS nanorods exhibit intense polarized emission along the rod main axis. The degree of linear polarization cannot be explained by dielectric effects alone, an additional electronic contribution is present whose nature has not been settled up to date. Using multi-band k.p theory, we analyse the potential influence of several factors affecting excitonic emission and show that shear strain is the main electronic mechanism promoting linear polarization. It favors energetically light hole excitons over heavy hole ones, via deformation potential, and makes their radiative recombination f…
Two-dimensional electron-hole gases in colloidal semiconductors have a wide variety of applications. Therefore, a proper physical understanding of these materials is of great importance. In this paper we present a detailed theoretical analysis of the recent experimental results by Tomar et al., that show an unexpected stability of excitons in CdSe nanoplatelets at high photoexcitation densities. Including the screening effects by free charges on the exciton properties, our analysis shows that CdSe nanoplatelets behave very differently from bulk CdSe, and in particular do not show a crossover t…
The blinking dynamics of colloidal core-shell CdSe/CdS dot-in-rods is studied in detail at the single particle level. Analyzing the autocorrelation function of the fluorescence intensity, we demonstrate that these nanoemitters are characterized by a short value of the mean duration of bright periods (ten to a few hundreds of microseconds). The comparison of the results obtained for samples with different geometries shows that not only the shell thickness is crucial but also the shape of the dot- in-rods. Increasing the shell aspect ratio results in shorter bright periods suggesting that surfac…
A new mechanism of electron paramagnetic resonance in spherical zinc-blende semiconductor nanocrystals, based on the extended orbital motion of electrons in the entire nanocrystal, is presented. Quantum confinement plays a crucial role in making the resonance signal observable. The mechanism remains operative in nanocrystals with uniaxially distorted shape. A theoretical model based on the proposed mechanism is in good quantitative agreement with unusual ODMR spectra observed in nearly spherical CdSe nanocrystals.
By combining an atomistic valence-force field approach and calculations based on the effective-mass approximation we investigate the influence of strain effects on the band alignment and general excitonic properties of core/shell CdSe/CdS dot/rod nanoparticles. We find that the inclusion of strain effects leads to an increase in exciton energy as well as to a decrease in electron and hole wave function overlap. Importantly, the native type-I band alignment of the CdSe/CdS material system is preserved and does not change into an quasi-type-II or even type-II band offset for the nanoparticles. F…
We present a theoretical description of excitons and positively and negatively charged trions in "giant" CdSe/CdS core-shell nanocrystals (NCs). The developed theory provides the parameters describing the fine structure of excitons in CdSe/CdS core/thick shell NCs as a function of the CdSe/CdS conduction band offset and the CdSe core radius. We have also developed a general theory describing the fine structure of positively charged trions created in semiconductor NCs with a degenerate valence band. The calculations take into account the complex structure of the CdSe valence band and inter-part…
We present theoretical and experimental investigations of the magnetism of paramagnetic semiconductor CdSe:Mn nanocrystals and propose an efficient approach to the exposure and analysis of the underlying anti-ferromagnetic interactions between magnetic ions therein. A key advance made here is the build-up of an analysis method with the exploitation of group theory technique that allows us to distinguish the anti-ferromagnetic interactions between aggregative Mn2+ ions from the overall pronounced paramagnetism of magnetic ion doped semiconductor nanocrystals. By using the method, we clearly rev…
We address spin properties and spin dynamics of carriers and charged excitons in CdSe/CdS colloidal nanoplatelets with thick shells. Magneto-optical studies are performed by time-resolved and polarization-resolved photoluminescence, spin-flip Raman scattering and picosecond pump-probe Faraday rotation in magnetic fields up to 30 T. We show that at low temperatures the nanoplatelets are negatively charged so that their photoluminescence is dominated by radiative recombination of negatively charged excitons (trions). Electron g-factor of 1.68 is measured and heavy-hole g-factor varying with incr…
We report on the experimental and theoretical studies of optical alignment and optical orientation effects in an ensemble of core/shell CdSe/CdS colloidal nanoplatelets. The dependences of three Stokes parameters on the magnetic field applied in the Faraday geometry are measured under continuous wave resonant excitation of the exciton photoluminescence. Theoretical model is developed to take into account both bright and dark exciton states in the case of strong electron and hole exchange interaction and random in-plane orientation of the nanoplatelets in ensemble. The data analysis allows us t…
The picosecond dynamics of excitons in colloidal CdSe nanorods are directly measured via their 1s to 2p-like internal transitions by ultra-broadband terahertz spectroscopy. Broadened absorption peaks from both the longitudinal and transverse states are observed at 8.5 and 11 THz, respectively. The onset of exciton-LO phonon coupling appears as a bleach in the optical conductivity spectra at the LO phonon energy for times > 1 ps after excitation. Simulations show a suppressed exciton temperature due to thermally excited hole states being rapidly captured onto ligands or unpassivated surface sta…
ZnTe/CdSe/(Zn,Mg)Te core/double-shell nanowires are grown by molecular beam epitaxy by employing the vapor-liquid-solid growth mechanism assisted with gold catalysts. A photoluminescence study of these structures reveals the presence of an optical emission in the near infrared. We assign this emission to the spatially indirect exciton recombination at the ZnTe/CdSe type II interface. This conclusion is confirmed by the observation of a significant blue-shift of the emission energy with an increasing excitation fluence induced by the electron-hole separation at the interface. Cathodoluminescenc…
We develop a simple and scalable graphene patterning method using electron-beam or ultraviolet lithography followed by a lift-off process. This method, with the merits of: high pattern resolution and high alignment accuracy, free from additional etching or harsh process, universal to arbitrary substrates, compatible to Si microelectronic technology, can be easily applied to diverse graphene-based devices, especially in array-based applications, where large-scale graphene patterns are desired. We have applied this method to fabricate CdSe nanobelt (NB)/graphene Schottky junction solar cells, wh…
The surface of nominally diamagnetic colloidal CdSe nanoplatelets can demonstrate paramagnetism owing to the uncompensated spins of dangling bonds (DBSs). We reveal that by optical spectroscopy in high magnetic fields up to 15 Tesla using the exciton spin as probe of the surface magnetism. The strongly nonlinear magnetic field dependence of the circular polarization of the exciton emission is determined by the DBS and exciton spin polarization as well as by the spin-dependent recombination of dark excitons. The sign of the exciton-DBS exchange interaction can be adjusted by the nanoplatelet gr…
Circularly polarized optical excitation is used to demonstrate the efficient injection of spin-polarized excitons to individual self-assembled CdSe quantum dots in ZnSe barrier. The exciton spin-transfer is studied by means of polarization-resolved single dot spectroscopy performed in magnetic field applied in Faraday configuration. Detailed analysis of the neutral exciton photoluminescence spectra reveals the presence of exciton spin relaxation during its lifetime in a quantum dot. This process is seen for both nonmagnetic dots and those containing single Mn$^{2+}$ ions. Taking this into acco…
We perform photoluminescence excitation measurements on individual CdSe/ZnS nanocrystal quantum dots (NCQDs) at room temperature to study optical transition energies and broadening. The observed features in the spectra are identified and compared to calculated transition energies using an effective mass model. The observed broadening is attributed to phonon broadening, spectral diffusion and size and shape inhomogeneity. The former two contribute the broadening transitions in individual QDs while the latter contributes to the QD-to-QD variation. We find that phonon broadening is often not the …
Transport properties of artificial solids composed of colloidal CdSe nanocrystals (NCs) are studied from 6 K to 250 K, before and after annealing. Annealing results in greatly enhanced dark and photocurrent in NC solids, while transmission electron microscopy (TEM) micrographs show that the inter-dot separation decreases. The increased current can be attributed to the enhancement of inter-dot tunneling caused by the decreased separation between NCs and by chemical changes in their organic cap. In addition, the absorption spectra of annealed solids are slightly red-shifted and broadened. These …
CdSe colloidal nanoplatelets are studied by spin-flip Raman scattering in magnetic fields up to 5 T. We find pronounced Raman lines shifted from the excitation laser energy by an electron Zeeman splitting. Their polarization selection rules correspond to those expected for scattering mediated by excitons interacting with resident electrons. Surprisingly, Raman signals shifted by twice the electron Zeeman splitting are also observed. The theoretical analysis and experimental dependencies show that the mechanism responsible for the double flip involves two resident electrons interacting with a p…
Unveiling the local elemental arrangements across the interfaces inside CdSe/Cd1-xZnxS core-shell and CdSe/CdS/ Cd1-xZnxS core-crown-shell quantum wells
We present a polarization-resolved photoluminescence study of the exchange interaction effects in a prototype system consisting of an individual Fe2+ ion and a single neutral exciton confined in a CdSe/ZnSe quantum dot. Maximal possible number of eight fully linearly-polarized lines in the bright exciton emission spectrum is observed, evidencing complete degeneracy lifting in the investigated system. We discuss conditions required for such a scenario to take place: anisotropy of the electron-hole interaction and the zero-field splitting of the Fe2+ ion spin states. Neglecting of either of thes…
We present results for electronic transport measurements on large three-dimensional arrays of CdSe nanocrystals. In response to a step in the applied voltage, we observe a power-law decay of the current over five orders of magnitude in time. Furthermore, we observe no steady-state dark current for fields up to 10^6 V/cm and times as long as 2x10^4 seconds. Although the power-law form of the decay is quite general, there are quantitative variations with temperature, applied field, sample history, and the material parameters of the array. Despite evidence that the charge injected into the film d…
The exciton spin dynamics and polarization properties of the related emission are investigated in colloidal CdSe/CdS dot-in-rod (DiR) and spherical core/shell nanocrystal (NC) ensembles by magneto-optical photoluminescence (PL) spectroscopy in magnetic fields up to 15 T. It is shown that the degree of circular polarization (DCP) of the exciton emission induced by the magnetic field is affected by the NC geometry as well as the exciton fine structure and can provide information on nanorod orientation. A theory to describe the circular and linear polarization properties of the NC emission in mag…
A novel method to image charge is used to measure the diffusion coefficient of electrons in films of CdSe nanocrystals at room temperature. This method makes possible the study of charge transport in films exhibiting high resistances or very small diffusion coefficients.
The photon statistics of CdSe/CdS dot-in-rods nanocrystals is studied with a method involving post-selection of the photon detection events based on the photoluminescence count rate. We show that flickering between two states needs to be taken into account to interpret the single-photon emission properties. With post-selection we are able to identify two emitting states: the exciton and the charged exciton (trion), characterized by different lifetimes and different second order correlation functions. Measurements of the second order autocorrelation function at zero delay with post- selection s…
Doping a semiconductor quantum dot with just a single impurity atom can completely transform its physical properties. Here, we report and analyze the magnetic circular dichroism (MCD) spectra of colloidal CdSe quantum dot samples containing on average fewer than one Mn2+ per quantum dot. Even at this sub-single-dopant level, the low-temperature low-field data are dominated by impurity-induced Zeeman splittings caused by dopant-carrier sp-d exchange. Unlike in more heavily doped quantum dots, however, the MCD intensity at the first CdSe exciton shows a field-induced sign flip as the field stren…
We present a detailed spectroscopic study of the photoluminescence quenching in an epitaxial structures containing CdSe/ZnSe quantum dots doped with low concentration of Mn$^{2+}$ ions. Our time-resolved and time-integrated experiments reveal the origin of the quenching observed in macro-photoluminescence studies of ensembles of such dots. We show that incorporation of even a few ions to an individual dot does not quench its luminescence effectively, although some fingerprints of expected spin-dependent quenching are visible. At the same time, the presence of Mn$^{2+}$ ions in the sample signi…
Using semi-analytical models we calculate the energy, effective Bohr radius and radiative lifetime of neutral excitons confined in CdSe colloidal nanoplatelets (NPLs). The excitonic properties are largely governed by the electron-hole in-plane correlation, which in NPLs is enhanced by the quasi-two-dimensional motion and the dielectric mismatch with the organic environment. In NPLs with lateral size $L \gtrsim 20$ nm the exciton behavior is essentially that in a quantum well, with superradiance leading to exciton lifetimes of 1 ps or less, only limited by the NPL area. However, for $L < 20$ nm…
We present a magneto-optical study of individual self-assembled CdSe/ZnSe quantum dots doped with single Mn$^{2+}$ ions. Properties of the studied dots are analyzed analogously to more explored system of Mn-doped CdTe/ZnTe dots. Characteristic sixfold splitting of the neutral exciton emission line as well as its evolution in the magnetic field are described using a spin Hamiltonian model. Dynamics of both exciton recombination and Mn$^{2+}$ spin relaxation are extracted from a series of time-resolved experiments. Presence of a single dopant is shown not to affect the average excitonic lifetime…
ZnSe nanowire heterostructures were grown by molecular beam epitaxy in the vapour-liquid-solid growth mode assisted by gold catalysts. Size, shape and crystal structure are found to strongly depend on the growth conditions. Both, zinc-blende and wurtzite crystal structures are observed using transmission electron microscopy. At low growth temperature, cone-shaped nano-needles are formed. For higher growth temperature, the nanowires are uniform and have a high aspect ratio with sizes of 1-2 $μ$m in length and 20-50 nm in width as observed by scanning electron microscopy. Growing a nanowire on t…
Engineering semiconductors to enhance carrier multiplication (CM) could lead to increased photovoltaic cell performance and a significant widening of the materials range suitable for future solar technologies. Semiconductor nanocrystals (NCs) have been proposed as a favourable structure for CM enhancement, and recent measurements by transient absorption have shown evidence for highly efficient CM in lead chalcogenide and CdSe NCs. We report here an assessment of CM yields in CdSe and CdTe NCs by a quantitative analysis of biexciton and exciton signatures in transient photoluminescence decays. …
Cadmium selenide nanocrystal quantum dots (NC-QDs) are site-selectively synthesized by sequential ion beam implantation of selenium and cadmium ions in a SiO2 matrix through sub-micron apertures followed by a rapid thermal annealing step. The size, areal density and optical emission energy of the NC-QDs are controlled by the ion fluence during implantation and the diameter of implantation aperture. For low fluences and small apertures the emission of these optically active emitters is blue-shifted compared to that of the bulk material by $>100\,{\rm meV}$ due to quantum confinement. The emissi…
We study the band-edge exciton fine structure and in particular its bright-dark splitting in colloidal semiconductor nanocrystals by four different optical methods based on fluorescence line narrowing and time-resolved measurements at various temperatures down to 2 K. We demonstrate that all these methods provide consistent splitting values and discuss their advances and limitations. Colloidal CdSe nanoplatelets with thicknesses of 3, 4 and 5 monolayers are chosen for experimental demonstrations. The bright-dark splitting of excitons varies from 3.2 to 6.0 meV and is inversely proportional to …
The time-resolved photoluminescence (PL) characteristics of single CdSe/ZnS nanoparticles, embedded in a PMMA layer is studied at room temperature. We observe a strong spectral jitter of up to 55 meV, which is correlated with a change in the observed linewidth. We evaluate this correlation effect using a simple model, based on the quantum confined Stark effect induced by a diffusing charge in the vicinity of the nanoparticle. This allows us to derive a mean distance between the center of the particle and the diffusing charge of approximately 3.3 nm on average, as well as a mean charge carrier …
We experimentally investigated for the first time the lowest four band structure of Cd Se nanoplatelets at the r point of Brillouin zone [heavy-hole (hh), light-hole (lh) and two spin-orbital bands] and its modification due to the changing of the CdS shell thickness. The results of an experimental and theoretical study of exciton dynamics in colloidal CdSe/CdS nanoplateles are presented in the case of stationary laser excitation. The excitation was performed by means of the powerful nanosecond laser and the pump and probe technique was utilized. The differential transmission spectra peculiarit…
Coupled colloidal quantum dot molecules composed of two fused CdSe/CdS core/shell sphere monomers were recently presented. Upon fusion, the potential energy landscape is changing into two quantum dots separated by a pre-tuned potential barrier with energetics dictated by the conduction and valence band offsets of the core/shell semiconductors, and width controlled by the shell thickness and the fusion reaction conditions. In close proximity of the two nanocrystals, orbital hybridization occurs, forming bonding and anti-bonding states in analogy to the hydrogen molecule. In this study, we exami…
The recombination dynamics and spin polarization of excitons in CdSe nanocrystals synthesized in a glass matrix are investigated using polarized photoluminescence in high magnetic fields up to 30 Tesla. The dynamics are accelerated by increasing temperature and magnetic field, confirming the dark exciton nature of the low-temperature photoluminescence (PL). The circularly polarized PL in magnetic fields reveals several unusual appearances: (i) a spectral dependence of the polarization degree, (ii) its low saturation value, and (iii) a stronger intensity of the Zeeman component which is higher …
By performing spectroscopic single-particle measurements at cryogenic temperatures over the course of hours we study %By performing spectroscopic longtime single-particle measurements at cryogenic temperatures we study both the spectral diffusion as well as the diffusion of the decay rates of the fluorescence emission of core/shell CdSe/CdS dot/rod nanoparticles. A special analysis of the measurements allow for a correlation of data for single neutral excitons only, undisturbed by the possible emission of other excitonic complexes. We find a nearly linear dependency of the fluorescence decay r…
Although poorly understood, cation-exchange reactions are increasingly used to dope or transform colloidal semiconductor nanocrystals (quantum dots). We used density-functional theory and kinetic Monte Carlo simulations to develop a microscopic theory that explains structural, optical, and electronic changes observed experimentally in Ag-cation-exchanged CdSe nanocrystals. We find that Coulomb interactions, both between ionized impurities and with the polarized nanocrystal surface, play a key role in cation exchange. Our theory also resolves several experimental puzzles related to photolumines…
To understand and optimize optical spin initialization in room temperature CdSe nanocrystal quantum dots (NCQDs) we studied the dependence of the time-resolved Faraday rotation signal on pump energy $E_p$ in a series of NCQD samples with different sizes. In larger NCQDs, we observe two peaks in the spin signal vs. $E_p$, whereas in smaller NQCDs, only a single peak is observed before the signal falls to a low, broad plateau at higher energies. We calculate the spin-dependent oscillator strengths of optical transitions using a simple effective mass model to understand these results. The observe…
We study how shape affects multiexciton generation (MEG) rates in a semiconducting nanocrystal by considering CdSe nanorods with varying diameters and aspect ratios. The calculations employ an atomistic semiempirical pseudopotential model combined with an efficacious stochastic approach applied to systems containing up to 20,000 atoms. The effect of nanorod diameter and aspect ratio on multiexciton generation rates is analyzed in terms of the scaling of the density of trion states and the scaling of the Coulomb couplings. Both show distinct scaling from spherical nanocrystals leading to a surp…
Using a first-principle approach beyond density functional theory we calculate the electronic and optical properties of small diameter CdSe nanowires.Our results demonstrate how some approximations commonly used in bulk systems fail at this nano-scale level and how indispensable it is to include crystal local fields and excitonic effects to predict the unique optical properties of nanowires. From our results, we then construct a simple model that describes the optical gap as a function of the diameter of the wire, that turns out to be in excellent agreement with experiments for intermediate an…
We discuss photo-luminescence characteristics of CdSe core/shell quantum dots at cryogenic temperatures using a hybrid system of a single quantum dot and an optical nanofiber. The key point is to control the emission species of quantum dot to charged excitons, known as trions, which have superior characteristics to neutral excitons. We investigate the photocharging behavior for the quantum dots by varying the wavelength and intensity of irradiating laser light, and establish a method to create a permanently charged situation which lasts as long as the cryogenic temperature is maintained. The p…
We study the low-temperature magneto-photoluminescence (PL) from individual CdSe nanocrystals. Nanocrystals having a small "bright" exciton fine structure splitting ($<$0.5 meV) exhibit a conventional left- and right-circularly polarized Zeeman PL doublet in applied magnetic fields. In contrast, nanocrystals with large fine structure splitting ($>$1 meV) show an anomalous magneto-PL polarization, wherein the lower-energy peak becomes circularly polarized with increasing field, while the higher-energy peak remains linearly polarized. This unusual behavior arises from strong mixing between the a…
The electronic structure of CdSe/CdS core/shell seeded nanorods of experimentally relevant size is studied using a combination of molecular dynamics and semiempirical pseudopotential techniques, with the aim to address the transition from type-I to a quasi-type-II band alignment. The hole is found to be localized in the core region regardless of its size. The overlap of the electron density with the core region depends markedly on the size of the CdSe core: For small cores, we observe little overlap, consistent with type-II behavior. For large cores, significant core-overlap of a number of exc…
We report electroluminescence (EL) measurements carried out on three-terminal devices incorporating individual n-type CdSe nanowires. Simultaneous optical and electrical measurements reveal that EL occurs near the contact between the nanowire and a positively biased electrode or drain. The surface potential profile, obtained by using Kelvin probe microscopy, shows an abrupt potential drop near the position of the EL spot, while the band profile obtained from scanning photocurrent microscopy indicates the existence of an n-type Schottky barrier at the interface. These observations indicate that…
We investigate the time-resolved photocurrent response of CdSe quantum dot (QD) thin films sensitized with zinc beta-tetraaminophthalocyanine (Zn4APc) on three different substrates, namely silicon with 230 nm SiO2 dielectric, glass as well as polyimide. While Si/SiO2(230 nm) is not suitable for any transient photocurrent characterization due to an interfering photocurrent response of the buried silicon, we find that polyimide substrates invoke the larger optical bandwidth with 85 kHz vs. 67 kHz for the same quantum dot thin film on glass. Upon evaluation of the transient photocurrent, we find …
Colloidal 2D semiconductor nanoplatelets are highly efficient light emitters, which exhibit large absorption and emission cross sections, and constitute promising laser gain media. However, if dispersed in solutions, such nanoplatelets lack a suitable optical platform for scalable and application-oriented integration into optical setups such as lasers. Here, we demonstrate the first successful integration of solution-processed 2D CdSe/CdS Core/Crown nanoplatelets in m-scale liquid core optical fibers. We compare the nanoplatelets' spectroscopic properties before and after filling them into the…
Giant shell CdSe/CdS quantum dots are bright and flexible emitters, with near-unity quantum yield and suppressed blinking, but their single photon purity is reduced by efficient multiexcitonic emission. We report the observation, at the single dot level, of a large blueshift of the photoluminescence biexciton spectrum ($24\pm5$ nm over a sample of 32 dots) for pure-phase wurtzite quantum dots. By spectral filtering, we demonstrate a 2.3 times reduction of the biexciton quantum yield relative to the exciton emission, while preserving as much as 60% of the exciton single photon emission, thus im…
Tunneling of electrons through the barriers in heterostructures devices is investigated by using the unified Transfer Matrix Method. The effect of barrier width on electron transmission coefficients has also been examined for different pairs of semiconductor devices of significant research interest in current years. Such Pairs involve AlxGa1-xAs/GaAs, AlSb/InAs, and CdS/CdSe quantum barriers with varying dimensions reduced from 20 nm to 5nm to observe how tunneling properties are affected by scaling. The effective electron masses in the well and barrier regions typically vary with constituent …
We demonstrate high quantum yield broad photoluminescence emission of ultrathin sub-nanometer CdSe nanoplatelets (two-monolayer). They also exhibit polarization-characterized lateral size dependent anomalous heavy hole and light/split-off hole absorption intensities.
Magnetic doping of semiconductor nanostructures is actively pursued for applications in magnetic memory and spin-based electronics. Central to these efforts is a drive to control the interaction strength between carriers (electrons and holes) and the embedded magnetic atoms. In this respect, colloidal nanocrystal heterostructures provide great flexibility via growth-controlled `engineering' of electron and hole wavefunctions within individual nanocrystals. Here we demonstrate a widely tunable magnetic sp-d exchange interaction between electron-hole excitations (excitons) and paramagnetic manga…
