Single quantum emitters with spin ground states based on Cl bound excitons in ZnSe

Defects in wide-band-gap semiconductors are promising qubit candidates for quantum communication and computation. Epitaxially grown II-VI semiconductors are particularly promising host materials due to their direct band gap and potential for isotopic purification to a spin-zero nuclear background. Here, we show an alternative type of single photon emitter with potential electron spin qubits based on Cl impurities in ZnSe. We utilize a quantum well to increase the binding energies of donor emission and confirm single photon emission with short radiative lifetimes of 192 ps. Furthermore, we verify that the ground state of the Cl donor complex contains a single electron by observing two-electron-satellite emission, leaving the electron in higher orbital states. We also characterize the Zeeman splitting of the exciton transition by performing polarization-resolved magnetic spectroscopy on single emitters. Our results suggest single Cl impurities are suitable as a single photon source with a potential photonic interface.

Figure 1

(a) Crystal structure of ZnSe with a single Cl impurity replacing a Se atom. (b) Energy band diagram showing the ground state ($D^0$) and excited state ($D^{0}X$), along with the bound exciton and two-electron-satellite emission, shown as blue and red arrows. (c) Layer structure of the grown material with in situ doped Cl impurities in the ZnSe quantum well.

Figure 2

(a) Photoluminescence (PL) spectrum obtained with above band excitation, demonstrating free exciton ($FX$), trion ($X^{-}$), and bound exciton ($D^{0}X$) emission. (b) Image of localized photoluminescence from a single bound exciton complex. (c) Histogram showing the distribution of binding energies of $D^{0}X$ lines, with an average binding energy of 15 meV and a standard deviation of 6 meV. (d) Photoluminescence excitation spectrum of bound exciton line.

Figure 3

(a) Spectra showing the TES line with increasing resonant pump power. The horizontal axis represents energy separation below the $D^{0}X$ line. Spectra are offset for clarity. Dashed lines represent the background used to integrate the TES emission. (b) Background-corrected and integrated counts from the TES line.

Figure 4

(a) Power-dependent emission intensity of the bound exciton (blue) and free exciton (red). The inset shows a log scale view of the data. (b) Second-order autocorrelation function obtained from the $D^{0}X$ line, demonstrating single photon emission.

Figure 5

(a) Time-resolved photoluminescence measurement showing a biexponential decay with dominant fast decay component of 192 ps and slow decay component of 2.49 ns. (b) Linewidth of the $D^{0}X$ emission recorded as a function of temperature. (c) PL intensity recorded over 7 h showing the stability of the emitter.

Figure 6

(a) Optical selection rules under applied out-of-plane magnetic field. (b) Polarization-resolved photoluminescence spectrum recorded at increasing magnetic field intensity, showing the splitting into orthogonal circular polarizations.