We demonstrate the generation of triggered single photons at a predetermined and well defined energy using the radiative recombination of single nitrogen-bound excitons in a semiconductor. The nitrogen atoms are embedded in a ZnSe quantum well structure and were excited by nonresonant optical pumping (82 MHz) at low temperature (4 K). We find resolution-limited photoluminescence lines ($280\text{ }\ensuremath{\mu}\mathrm{e}\mathrm{V}$) which display photon antibunching under continuous optical pumping. Our results also suggest that single nitrogen-bound excitons are well suited for cavity quantum electrodynamics experiments.

Quantum optical studies on individual acceptor bound excitons in a semiconductor.

Achieving significant doping in GaAs/AlAs core/shell nanowires (NWs) is of considerable technological importance but remains a challenge due to the amphoteric behavior of the dopant atoms. Here we show that placing a narrow GaAs quantum well in the AlAs shell effectively getters residual carbon acceptors leading to an unintentional p-type doping. Magneto-optical studies of such a GaAs/AlAs core–multishell NW reveal quantum confined emission. Theoretical calculations of NW electronic structure confirm quantum confinement of carriers at the core/shell interface due to the presence of ionized carbon acceptors in the 1 nm GaAs layer in the shell. Microphotoluminescence in high magnetic field shows a clear signature of avoided crossings of the n = 0 Landau level emission line with the n = 2 Landau level TO phonon replica. The coupling is caused by the resonant hole-phonon interaction, which points to a large two-dimensional hole density in the structure.

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Unintentional high-density p-type modulation doping of a GaAs/AlAs core-multishell nanowire.

A series of Be δ-doped GaAs/AlAs multiple-quantum wells with the doping at the well center were grown by molecular beam epitaxy. The photoluminescence spectra were measured at 4, 20, 40, 80, 120, and 200 K, respectively. The two-hole transitions of the acceptor-bound exciton from the ground state, 1S3/2(Γ6), to the first-excited state, 2S3/2(Γ6), have been clearly observed and the acceptor binding energy measured. A variational calculation is presented to obtain the acceptor binding energy as a function of well width. It is found that the experimental results are in good agreement with the theory.

/pdf/acceptor-binding-energy-in-d-doped-gaas-alas-multiple-3vbo9c2xo4.pdf

Acceptor binding energy in δ-doped GaAs/AlAs multiple-quantum wells

We have investigated the optical transitions in Be $\ensuremath{\delta}$-doped $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{As}$ multiple quantum wells with various width and doping levels. The fractional dimensionality model was extended to describe free-electron--acceptor (free hole-donor) transitions in a quantum well. The measured photoluminescence spectra from the samples were interpreted within the framework of this model, and acceptor-impurity induced effects in the photoluminescence line shapes from multiple quantum wells of different widths were demonstrated.

Excitonic and impurity-related optical transitions in Be δ-doped GaAsAlAs multiple quantum wells: Fractional-dimensional space approach

Pump-probe experiments are used to characterize Fe-doped InGaAs/InP multiple quantum wells for ultrafast saturable absorption applications. Sample photoresponse time is well controlled by iron doping from the nanosecond range to a value as short as 0.45 ps for an iron concentration of 6×1018 cm−3. Furthermore, the switching amplitude, that is, the differential transmission ratio (DTR), of samples having increasing Fe doping (null to 6×1018 cm−3) presents two decreasing regimes at moderate optical excitation levels. The first one is explained well by the degree of quality of the material, whereas the second one is interpreted as an inhibition of exciton formation at high doping levels. This interpretation is highlighted by an analysis of the temporal evolution of the DTR. The influence of the doping localization (in the well, in the barrier, or in the whole structure) is studied as well. Finally, an attractive way to maintain a constant value of the DTR with an ultrafast response time (2.6 ps) is proposed ...

Ultrashort, nonlinear, optical time response of Fe-doped InGaAs/InP multiple quantum wells in 1.55-μm range

Exciton properties in p-type GaAs/AlxGa1-xAs quantum wells in the high doping regime

Thermally activated intersubband and hopping transport in center-doped p-type GaAs/AlxGa1-xAs quantum wells.

An optical study of the excited states of shallow acceptors confined in narrow GaAs/Al x Ga 1-x As quantum wells (QW's) is presented. The excited states have been investigated via the two-hole transitions (THT's) of the bound exciton recombination observed in selective photoluminescence (SPL) and photoluminescence excitation (PLE) spectroscopy. Several heavy-hole (hh)-like excited nS (Γ 6 ) acceptor states dominate the satellite spectrum, but also the light-hole (lh)-like excited 2S (Γ 7 ) acceptor state has been observed in these SPL spectra. In addition, the THT corresponding to the parity-forbidden transition to the 2P 3/2 excited state has been observed

Excited states of shallow acceptors confined in GaAs/AlxGa1-xAs quantum wells.

Hydrogen passivation of high quality AlGaAs/GaAs:Be quantum wells (QWs) is studied by photoluminescence (PL) spectroscopy. The interaction of hydrogen with both Be dopants and QW interfaces is analyzed. The efficiency of Be acceptor passivation by hydrogen is shown to be dependent on the Be concentration. By comparing the PL spectra of the QW structures with different doping level, before and after hydrogenation, a partial (up to 50%) deactivation of Be atoms is revealed. It is also shown that a prolonged hydrogenation strongly degrades the interface sharpness, presumably due to hydrogen‐enhanced intermixing.

A. C. Ferreira

Papers

Exciton properties in p-type GaAs/AlxGa1-xAs quantum wells in the high doping regime

Thermally activated intersubband and hopping transport in center-doped p-type GaAs/AlxGa1-xAs quantum wells.

Excited states of shallow acceptors confined in GaAs/AlxGa1-xAs quantum wells.

Effect of hydrogen passivation on Be‐doped AlGaAs/GaAs quantum wells

Many-body effects in highly acceptor-doped GaAs/Al x Ga 1-x As quantum wells