Quantum confined Stark effect

Empedocles S A and Bawendi M G 1997 Quantum-confined Stark effect in single CdSe nanocrystalline quantum dots Science 278 2114-17... 

Empedocles, S. A. and Bawendi, M. G. (1997) Quantum-confined stark effect in single CdSe nanocrystallite quantum dots. Science, 278, 2114-2117. 

Significant differences in the optical signatures of Eu3+ ions were observed between GaN Eu QDs and GaN Eu layers (Andreev et al., 2005b) (1) the emission fine at 633.5 was not observed in GaN Eu QDs for unknown reason (2) the 5Do 7F2 transition was red shifted by 1.7 nm in QDs compared to the layer sample, which could be induced by a strong internal electric filed in QDs (quantum confinement Stark effect) (3) the PL intensity is almost temperature independent for GaN Eu QDs, but sensitive to temperature for GaN Eu layers (Hori et al., 2004). 

QB QCA QCSE QE QMS QW quantum barrier quasi-cubic approximation quantum-confined Stark effect quantum efficiency quadrupole mass spectrometry quantum well... 

It was previously demonstrated theoretically [1] and experimentally [2] that semiconductor quantum dots (QDs) show strong dependence of optical properties on an electric field. Chemically synthesized semiconductor nanorods also exhibit the electric field effects. For example, quantum-confined Stark effect and luminescence quenching of single nanorods were previously demonstrated [3-5]. Unlike QDs, the nanorods exhibit quantum confinement only in two dimensions. It is reasonable to assume that the electric field applied along a nanorod may result in the strong polarization dependence of photoluminescence (PL). In the present paper, we investigate the influence of an external electric field onto luminescent properties of chemically synthesized CdSe/ZnS nanorods. 

The curves in Fig. 1 demonstrate the decrease of PL intensity (quenching) and the red shift of PL maximum with the voltage increased. At the values of electrical field strength E up to 10 V/cm the PL of nanorods is quenched more than PL of QDs. However, the wavelength shift of PL maximum with applied electric field for nanorods increases very weak. Evidently, due to the elongated shape of nanorods, the external electric field effect may differ for S- and P-polarized PL. This property is important for application of this material in optoelectronic nanodevices. To understand reasons of the electric field effect difference between QDs and nanorods, the mechanism of nanorods PL quenching has to be studied. The quantum-confined Stark effect is probably not the single factor in force. 

Optoelectronic nanodevices that rely on electric field effects in optical absorption and emission provide the ability to be controlled conveniendy using integrated electronic platforms. Semiconductor quantum dots are theoretically expected as an excellent candidate for such optoelectronic nanomaterials to show optical properties strongly dependent on electric field [1]. In the general class of quantum dots, chemically synthesized semiconductor nanocrystals also exhibit electric field effects, for example, as demonstrated in their optical absorption (e.g. the quantum confined Stark effect [2,3]) and in their optical emission as the Stark shift and luminescence quenching [4,5]). 

For the polar samples, the transition energy was red-shifted because of the quantum-confined Stark effect. The position of the transition energy for the nonpolar structures strictly followed the results of the calculations for a flat band model, including corrections for exciton binding energies. It is reasonable to associate this fact with the disappearance of built-in electric flelds along the (1120) growth direction. 

The spontaneous emission of C-plane (In,Ga)N quantum wells is determined by both the electron-hole wavefunctions separation due to the built-in internal electrostatic field (quantum-confined Stark effect) and exciton local-i2ation caused by potential fluctuations [71-74]. The reali2ation of M-plane (In,Ga)N/GaN MQWs allows us to investigate the impact of exciton locali2ation on radiative recombination without the influence of internal electrostatic fields. To study the recombination mechanism of M-plane (In,Ga)N/GaN MQWs, continuous-wave photoluminescence (cw-PL) spectroscopy and time-resolved (TR) PL were carried out. 

However, for polar heterostructures in the III-N system (i.e. for QWs or QDs grown along the [0001] direction of the noncentrosymmetric wurtzite structure), optical properties are usually dominated by the quantum confined Stark effect resulting from the internal field [5]. The confined electrons and... 

GaN band gap owing to the quantum confined Stark effect [4]. This is a first indication that the effects of the internal electric field are reduced compared to polar QDs [19, 43]. The PL spectrum does not evolve as a function of excitation power density over 6 orders of magnitude, which shows that no screening or state filling effects are observed in our CW experiments. 

Light emitters based on nitride semiconductors typically consist of [0001]-oriented quantum wells (QWs) [1] where the quantum confinement Stark effect (QCSE) is caused by piezoelectric and spontaneous polarizations, which lower the optical transition probability [2, 3]. To circumvent this issue, several groups have tried to fabricate InGaN/GaN and GaN/AlGaN QWs on nonpolar planes such as the 1100 plane (m-plane) [4] and the (1120) plane (a-plane) [5-7]. However, owing to the difficulty in growing high-quality crystals in nonpolar directions, the layers contain numerous nonradiative recombination centers. 

QCSE quantum confined Stark effect SM semimetal... 

Ga)N MQWs because, in addition to misfit, if the lattice constant of the well layer differs from that of the barrier layer in a wurtzite structure, strain field exists inside the well layers, which causes polarization charge and the associated quantum-confined Stark effect. 

Still insufficient compared to the classical III-V semiconductors. This applies even more to semipolar and nonpolar surfaces of these materials, which have started to gain more attention recently. One of the reasons is that nitride layers grown on nonpolar and semipolar surfaces are less influenced by the quantum-confined Stark effect, which hmits the performance of optoelectronic devices. 

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