Photoluminescence from single isoelectronic traps in nitrogen delta-doped GaAs grown on GaAs(1 1 1)A

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Abstract

We have studied photoluminescence (PL) observed from single isoelectronic traps formed by nitrogen pairs in nitrogen δ-doped GaAs layers grown on GaAs(1 1 1)A substrates. The PL was composed of a single peak with a narrow linewidth of ∼80 μeV. Polarized PL measurements confirmed that the emission from single isoelectronic traps in nitrogen δ-doped GaAs(1 1 1) is unpolarized irrespective of nitrogen pair arrangements. These results can be explained by in-plane isotropy of the samples, which is consistent with the symmetrical property of GaAs(1 1 1), and demonstrate that utilizing (1 1 1) substrate is an effective means for obtaining unpolarized single photons, which are desirable for the application to quantum cryptography.

Introduction

Single-photon emitters are expected to play a key role in the field of quantum information science and technology, such as quantum cryptography [1], [2] and quantum computing [3]. In order to realize the single-photon emitters, several candidates are proposed, for example, single molecules [4], nitrogen-vacancy centers in diamond [5], acceptors in semiconductors [6] and semiconductor quantum dots [7], [8]. Single isoelectronic traps in semiconductors [9], [10], [11] are also promising candidates for single-photon emitters. Concerning the isoelectronic traps in nitrogen doped GaAs or GaP, the emission energies correspond to the configuration of nitrogen pairs [12], [13]. In addition, the linewidth of the emission from the isoelectronic traps formed by nitrogen pairs in GaAs or GaP is considerably narrow. Therefore, when utilizing the isoelectronic traps, sharp emission lines with well-defined wavelengths are readily obtained, which is advantageous to the design of distribution Bragg reflectors or filters for enhancing and selecting single photons with specific energies, unlike using semiconductor quantum dots. Thus, we have studied the luminescence from single isoelectronic traps formed by nitrogen pairs in GaAs to demonstrate the potential for the single-photon emitters. We succeeded in observing exciton emission lines from single isoelectronic traps formed by nitrogen pairs in nitrogen δ-doped GaAs layers grown on GaAs (0 0 1) surface [12], and reported twin emission lines which are linearly polarized in the [1 –1 0] and [1 1 0] directions, respectively [13]. Although similar level splitting and polarization properties were reported for semiconductor quantum dots [14], which is due to anisotropic shape of quantum dots, such polarization properties are not suitable for the application to quantum cryptography using unpolarized single photons, such as BB84 protocol [15].

Thus, we have studied photoluminescence from isoelectronic traps in nitrogen δ-doped GaAs grown on GaAs (1 1 1)A substrates which show isotropic in-plane crystal symmetry in principle to obtain randomly polarized photons.

Section snippets

Experimental procedure

The samples used in this study were nitrogen δ-doped GaAs layers grown on a semi-insulating undoped GaAs (1 1 1)A substrates by low-pressure metalorganic vapor phase epitaxy. The sources were trimethylgallium (TMG), tertiarybutylarsine (TBA) and dimethylhydrazine (DMHy). The growth temperatures were 630 and 600 °C. To perform nitrogen δ-doping into GaAs, we supplied DMHy flow during the interruption of TMG flow for a few seconds. The nitrogen δ-doped layer was sandwiched between a 300-nm-thick

Results and discussion

Fig. 1 shows a PL intensity map of nitrogen δ-doped GaAs grown on a (1 1 1)A substrate obtained by scanning the sample in one direction. As can be seen from this map, one PL line with narrow linewidth is observed at a specific position, clearly indicating that the emission from a single isoelectronic trap can be successfully detected. This PL line is located at 1.447 eV, which is in agreement with the energy reported for the emission line due to NND[8]. Somewhat large spatial distribution (∼3 μm)

Conclusions

We have observed exciton emission from single isoelectronic traps in nitrogen δ-doped GaAs grown on GaAs (1 1 1)A surface by high energy resolution micro-PL spectroscopy. The emission from single isoelectronic traps formed by any nitrogen pair exhibited single-peak and unpolarized character. This result shows that the in-plane strain is isoctropic in nitrogen δ-doped GaAs(1 1 1), which is consistent with the crystal symmetry, and demonstrates that the growth on (1 1 1) surface is effective means for

Acknowledgment

This study was partially supported by Grant-in-Aid for Scientific Research (B) (No. 21360004), Japan Society for the Promotion of Science.

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