{'fraction_non_alphanumeric': 0.034253194459357886, 'fraction_numerical': 0.017287662407387522, 'mean_word_length': 4.689676237018937, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 1, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Bright single photon sources in lateral silicon carbide light emitting diodes

Single-photon emitting devices have been identified as an important building block for applications in quantum information and quantum communication. They allow to transduce and collect quantum information over a long distance via photons as so called flying qubits. In addition, substrates like silicon carbide provides an excellent material platform for electronic devices. In this work we combine these two features and show that one can drive single photon emitters within a silicon carbide p-i-n-diode. To achieve this, we specifically designed a lateral oriented diode. We find a variety of new color centers emitting non-classical lights in VIS and NIR range. One type of emitter can be electrically excited, demonstrating that silicon carbide can act as an ideal platform for electrically controllable single photon sources.

Many color centers in wide-bandgap semiconductors are considered as prominent quantum light sources owing to their stability, brightness, and spin-dependent properties [1][2][3][4][5] . Despite the wealth color centers found, there is an ongoing demand in e.g. quantum communication, information processing and sensing to explore new candidate defects. Since color centers are point defects, whose excited states can decay radiatively, searching natural materials or artificially grown but impure crystals may allow for identifying new color centers 6,7 . In addition, artificially adjusted material properties can lead to the creation of optical and spin active color centers. For example, by gradually adjusting both donor and acceptor impurity concentrations across a chemical vapor deposition (CVD) grown diamond crystal, the neutral silicon vacancy center could be reproducible created via charge state alignment 8 . While most color centers are driven optically, electric excitation provides another method to drive optical transitions. Furthermore it provides an efficient way to integrate quantum light sources into compact electronic devices 9 , as there is no need for an additional bulky laser system.
In this report, we fabricate lateral silicon carbide (SiC) diodes by ion implantation of donor and acceptor impurities forming 20 m wide p-i-n junctions in a nearly twodimensional layer. This structure provides easy optical access to three distinctive layers, in which the Fermi-level is modulated over a wide energy range. In addition, because efficient carrier injection is possible, our structure provides an opportunity to look for electrically driven color centers. Similar lateral p-i-n junctions on diamond surface were reported, to study charge state conversion and electrical excitation of the nitrogen-vacancy centers in diamond 10 . However, the inherent properties of diamond disallow efficient doping, e.g. mismatch of depth of doped layers due to adverse production of thick graphite layers on the surface 10,11 . SiC is known to be an industry friendly platform, whose doping by ion implantation is very efficient 12 . Furthermore, ion implantation allows localized doping in the sub-microscopic scale, making it a highly necessary technique for scalable quantum device fabrication 10,13 . Besides the wellstudied color centers in silicon carbide such as the silicon vacancy and divacancy, 4,14-16 several bright new color centers have been identified in bulk SiC substrate and electronic and optoelectronic devices 13,[17][18][19][20] . Among recent reports, a p-n junction was used to electrically excite the silicon antisite defect 13 . While p-n junctions allows efficient carrier injection, incorporation of an intrinsic layer as in our study is beneficial, as it allows gradual Fermi-level tuning in a wide area. It may enhance the chance to find new color centers, with enhancing brightness in SiC as suggested recently 21 . Here, we demonstrate varying optical properties of various color center, hitherto unknown single photon sources in 4H-SiC lateral p-i-n diodes including one which can be electrically pumped. We investigate their fluorescence spectra decay dynamics as a function of optical or electrical pump power.
A large part of the fabricated lateral p-i-n devices is presented in the optical microscope image in Fig. 1(a). The p-i-n diodes were fabricated on a vertical stack of epilayers that was grown by CVD with the following structure: n + 4H-SiC substrate/semi-insulating (SI) layer (10 µm thick)/n − (17 µm thick). SI layer was grown through in-situ vanadium doping during growth using vanadium tetrachloride (VTC) in bubbler configuration 22 A high concentration of vanadium is known to produce extended defects in the epilayer. The flow rate of VTC was optimized to achieve defect free epilayer with SI properties (resistivity >10 5 cm). The n − layer was grown under Silimited condition to ensure low n-type residual doping of nitrogen. The free carrier concentration of the undoped n − layer at room temperature is in the range mid-to-high n − layers were grown in a single growth run to avoid the formation of new defects at the interface.
N-and p-layers were created using phosphorus (P) and aluminum (Al) implantation, respectively at 800 C. Three-fold implantation of P + (200, 140 and 80 keV) and Al + (110, 75 and 50 keV) was carried out to obtain donor and acceptor concentrations of 2x10 20 and 5x10 19 cm -3 , respectively. Implantation depth have been designed to 300 nm for n-and 200 nm for p-layers. After ion implantation, samples were annealed at 1800 C for 5 min in an Ar atmosphere. To avoid surface degradation 23 , the sample surface has been covered with a carbon film during high temperature annealing. A 45 nm thick field oxide layer was formed on the SiC surface using pyrogenic oxidation (H2:O2 = 1:1) at 1100 C. To get electronic access to our device, metal electrodes on n-and p-layers have been formed by Al evaporation and lithography with liftoff technique. Each of these diodes can be individually addressed via the created top Al electrodes. While each p-doped region is covered by its own Al electrode, the n-layers are connected all together with a common Al electrode. In Fig. 1(b), a schematic of the p-i-n diodes with 20 µm width is illustrated. The n-layer is separated from the p-layer by an intrinsic layer (10 µm long). The top electrodes are shown in grey and are placed on top of the n-and p-layers, respectively. Note that this design is also used for a similar study reporting new color centers at the oxidized silicon carbide surface 20 . A typical bias-current measurement curve is plotted in Fig. 1(c), illustrating the typical diode behavior. The device is mounted on a home-built confocal microscope 4 , equipped with single photon counting modules (SPCMs) and an high NA oil objective (NA=1.35) to monitor luminescence. One resulting raster scan image with applied forward current (100 µA) is presented in Fig. 1(d). Here, purely electroluminescence (EL) from color centers is detected, i.e. no optical excitation is applied. The emitted light is mainly condensed around the interface of p-and n-layers, but also distinct emitters are found in the i-layer.
These isolated emitters in the i-layer are further investigated. The zoom-in of figure   1(d), indicated by a green rectangle, is shown in Fig. 2 This process can be interpreted as a closed cycle because both carrier injection occur only when the excited and ground state of a single electron is unoccupied. As we observe no bunching, which typically indicates an shelving process to an intermediate state 25 , we consider a two-level system consisting of a ground and excited state. We describe the electrical pumping by a rate 12 in analogy to a single photon absorption process, and the radiative decay rate by 21 . The background corrected 26 (2) ( ) curves will then effectively be a two-level system 25 17,19,20 . To investigate further, the same area is raster scanned confocally with 730 nm laser illumination without applying any bias. The same emitter stays dark in PL scan. Instead, many similar emitters can be found. The PL spectrum of a representing one, labeled with black circle in Fig. 2(b), gives rise to a maximum at around 800 nm.
In contrast to the EL emitter, the PL detected (2) ( ) curves in Fig. 3( We also investigate the polarization of the emitted single photons. Both emitter types show very well linear polarized dipole pattern as shown in Fig. 4(a) and (b). Note that non-ideal linear polarization could be found from some of the found PL emitters as can be seen in Fig. 4(a). Because bright and inhomogeneous background emission could be found often around such emitter, we ascribe it to imperfect background correction.  Their PL spectra are red-shifted [see Fig. 2(f)] compared to the EL and PL emitters found in the irradiated device. Note that PL spectra of these emitters are also not identical to any color centers recently reported 17,19,20,27 . Due to the spectral difference, we conclude, that the PL emitters found in the irradiated device are indeed due to electron irradiation. Due to the limited number of working devices, we could not test if the EL emitters are also observable in the non-irradiated device.
In summary, we found new color centers in both electron irradiated and non-