Tuning photoluminescence of single InAs quantum dot by electric field

By using photoluminescence (PL) and time-resolved PL spectra, the optical properties of single InAs quantum dot (QD) embedded in the p-1-n structure have been studied under an applied electric field With the increasing of electric field, the exciton lifetime increases due to the Stark effect. We noticed that the decrease or quenching of PL intensity with increasing the electric field is mainly due to the decrease of the carriers captured by QD.

Single-photon emission from a single InAs quantum dot

Excitation power-dependent micro-photoluminescence spectra and photon-correlation measurement are used to study the optical properties and photon statistics of single InAs quantum dots. Exciton and biexciton emissions, whose photoluminescence intensities have linear and quadratic excitation power dependences, respectively, are identified. Under pulsed laser excitation, the zero time delay peak of second order correlation function corresponding to exciton emission is well suppressed, which is a clear evidence of single photon emission.

Electrically Driven InAs Quantum-Dot Single-Photon Sources

Electrically driven single photon source based on single InAs quantum dot (QDs) is demonstrated. The device contains InAs QDs within a planar cavity formed between a bottom AlGaAs/GaAs distributed Bragg reflector (DBR) and a surface GaAs-air interface. The device is characterized by I-V curve and electroluminescence, and a single sharp exciton emission line at 966nm is observed. Hanbury Brown and Twiss (HBT) correlation measurements demonstrate single photon emission with suppression of multiphoton emission to below 45% at 80K

Dephasing rate in an InAs/GaAs single-electron quantum dot qubit

We have obtained the parameter-phase diagram, which unambiguously defines the parameter region for the use of InAs/GaAs quantum dot as two-level quantum system in quantum computation in the framework of the effective-mass envelope function theory. Moreover, static electric field is found to efficiently prolong decoherence time. As a result, decoherence time may reach the order of magnitude of milli-seconds as external static electric field goes beyond 20 kV/cm if only vacuum fluctuation is taken as the main source for decoherence. Our calculated results are useful for guiding the solid-state implementation of quantum computing.

InAs/GaAs single-electron quantum dot qubit

The time evolution of the quantum mechanical state of an electron is calculated in the framework of the effective-mass envelope function theory for an InAs/GaAs quantum dot. The results indicate that the superposition state electron density oscillates in the quantum dot, with a period on the order of femtoseconds. The interaction energy E-ij between two electrons located in different quantum dots is calculated for one electron in the ith pure quantum state and another in the jth pure quantum state. We find that E-11]E-12]E-22, and E-ij decreases as the distance between the two quantum dots increases. We present a parameter-phase diagram which defines the parameter region for the use of an InAs/GaAs quantum dot as a two-level quantum system in quantum computation. A static electric field is found to efficiently prolong the decoherence time. Our results should be useful for designing the solid-state implementation of quantum computing. (C) 2001 American Institute of Physics.

Fabrication and modulation characteristics of 1.3 mu m p-doped InAs quantum dot vertical cavity surface emitting lasers

We present the fabrication of 1.3 mu m waveband p-doped InAs quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) with an extremely simple process. The continuous-wave saturated output power of 1.1 mW with a lasing wavelength of 1280 nm is obtained at room temperature. The high-speed modulation characteristics of p-doped QD VCSELs of two different oxide aperture sizes are investigated and compared. The maximum 3 dB modulation bandwidth of 2.5 GHz can be achieved at a bias current of 7 mA for a p-doped QD VCSEL with an oxide aperture size of 10 mu m in the small signal frequency response measurements. The crucial factors for the 3 dB bandwidth limitation are discussed according to the parameters' extraction from frequency response.

Single-exciton spectroscopy of single Mn doped InAs quantum dots

The optical spectroscopy of a single InAs quantum dot doped with a single Mn atom is studied using a model Hamiltonian that includes the exchange interactions between the spins of the quantum dot electron-hole pair, the Mn atom, and the acceptor hole. Our model permits linking the photoluminescence spectra to the Mn spin states after photon emission. We focus on the relation between the charge state of the Mn, A0 or A−, and the different spectra which result through either band-to-band or band-to-acceptor transitions. We consider both neutral and negatively charged dots. Our model is able to account for recent experimental results on single Mn doped InAs photoluminescence spectra and can be used to account for future experiments in GaAs quantum dots. Similarities and differences with the case of single Mn doped CdTe quantum dots are discussed.

Quantum-confined Stark effects in a single GaN quantum dot

Using analytical expressions for the polarization field in GaN quantum dot, and an approximation by separating the potential into a radial and an axial, we investigate theoretically the quantum-confined Stark effects. The electron and hole energy levels and optical transition energies are calculated in the presence of an electric field in different directions. The results show that the electron and hole energy levels and the optical transition energies can cause redshifts for the lateral electric field and blueshifts for the vertical field. The rotational direction of electric field can also change the energy shift.

Fine structural splitting and exciton spin relaxation in single InAs quantum dots

We have studied the exciton spin dynamics in single InAs quantum dots (QDs) with different exciton fine structural splitting (FSS) by transient luminescence measurements. We have established the correlation between exciton spin relaxation rate and the energy splitting of the FSS when FSS is nonzero and found that the spin relaxation rate in QD increases with a slope of 8.8x10(-4) ns(-1) mu eV(-1). Theoretical analyses based on the phonon-assisted relaxations via the deformation potential give a reasonable interpretation of the experimental results.

Investigation of Electronic Energy Levels in InAs Quantum Dot with Shape of Lens by Using B-Spline Technique

The dependence of the electronic energy levels on the size of quantum dots (QDs) with the shape of spherical lens is studied by using the B-spline technique for the first time. Within the framework of the effective-mass theory, the values of electronic energy levels are obtained as a function of the height, radius and volume of QDs, respectively. When the height or radius of QDs increases, all the electronic energy levels lower, and the separations between the energy levels decrease. For lens-shape QDs, height is the key factor in dominating the energy levels comparing with the effect of radius, especially in dominating the ground-state level. These computational results are compared with that of other theoretical calculation ways. The B-spline technique is proved to be an effective way in calculating the electronic structure in QDs with the shape of spherical lens.

Electron spin relaxation by nuclei and holes in single InAs quantum dots

Electron spin relaxation of charged excitons X+ and X2+ are investigated by time-resolved and polarization-resolved photoluminescence spectroscopy. For X+ configuration, the electron spin relaxation shows a typical decay curve induced by hyperfine interaction with nuclei, whereas for X2+ state the electron spin relaxation is affected not only by nuclei but also by electron-hole exchange interaction, leading to a power-law time dependence.

Correlations between antibunching and blinking of photoluminescence from a single CdSe quantum dot

The antibunching and blinking from a single CdSe/ZnS nanocrystal with an emission wavelength of 655 nm were investigated under different excitation powers. The decay process of the photoluminescence from nanocrystal was fitted into a stretched exponential, and the small lifetime and the small stretching exponent under a high excitation power were explained by using nonradiative multi-channel model. The probability of distributions for off-times from photoluminescence intermittence was fitted into the power law, and the power exponents were explained by using a tunneling model. For higher excitation power, the Auger-assisted tunneling model takes effect, where the tunneling rate increases and the observed lifetime decreases. For weak excitation power, the electron directly tunnels between the nanocrystal and trapping state without Auger assistance. The correlation between antibunching and blinking from the same nanocrystal was analyzed.

Spin Relaxation of Electrons in Single InAs Quantum Dots

By using polarization-resolved photoluminescence spectra, we study the electron spin relaxation in single InAs quantum dots (QDs) with the configuration of positively charged excitons X+ (one electron, two holes). The spin relaxation rate of the hot electrons increases with the increasing energy of exciting photons. For electrons localized in QDs the spin relaxation is induced by hyperfine interaction with the nuclei. A rapid decrease of polarization degree with increasing temperature suggests that the spin relaxation mechanisms are mainly changed from the hyperfine interaction with nuclei into an electron-hole exchange interaction.

Optical transitions of positively charged excitons and biexcitons in single InAs quantum dots

National Basic Research Program of China 2007CB924904;Chinese Academy of Sciences KICX2.YW.W09-1

Study of self-assembled InAs quantum dot structure covered by InxGa1-xAs(0 <= x <= 0.3) capping layer

InAs self-assembled quantum dots(QDs) covered by 3-nm-thick InxGa1-xAs(0 less than or equal tox less than or equal to0.3) capping layer have been grown on GaAs(100) substrate. Transmission electron microscopy shows that InGaAs layer reduces the strain in the InAs islands,and atomic force microscopy evidences the deposition of InGaAs on the top of InAs islands when x = 0.3.The significant redshift of the photoluminescence (PL) peak energy and the reduction of PL linewidth of InAs quantum dots covered by InGaAs are observed. In addition,InGaAs overgrowth layer suppresses the temperature sensitivity of PL peak energy. Based on our analysis, the strain-reduction and the size distribution of the InAs QDs are the main cause of the redshift and temperature insensitivity of the PL respectively.