鈥淧recise lithographic alignment to site-controlled quantum dots is of major importance for numerous nano-photonic, nano-electronic and nano-spintronic devices,鈥� Sven H枚fling tells 麻豆淫院Org.com.

H枚fling continues: 鈥淪o far, most of the devices based on single quantum dots use a layer of self-organized quantum dots, where the dots are at random positions and a post-fabrication screening is employed to select devices with proper spectral and spatial alignment, for example, with respect to a cavity mode. After all, whether or not you can find a proper quantum dot is largely a matter of chance鈥�

H枚fling and his colleagues at Julius Maximilians University in W眉rzburg, Germany believe that they have come up with a scheme that would make it much easier to produce single dot-based devices to be used in the fabrication process of nano devices. The results from the team in W眉rzburg are reported in Applied 麻豆淫院ics Letters: 鈥淟ithographic alignment to site-controlled quantum dots for device integration.鈥�

鈥淧reviously used approaches were sufficient for the realization of single, research type devices, whose main purpose is the study of basic physics,鈥� H枚fling concedes, 鈥渂ut it does not allow for large scale device fabrication needed for widespread applications.鈥� Right now, he points out, in many cases the yield of these nano devices is close to zero.

In order to usher in an era of widespread applications for nano devices, the W眉rzburg team combined two processes to produce single dot device with higher yield: a site-controlled quantum dot growth by pre-patterning and an accurate alignment technique. 鈥淧eople have pioneered this pre-patterned quantum dot growth before,鈥� says H枚fling. 鈥淥thers have made accurate alignment. By combining them together, we are investigating a serious scheme that is scalable. This will significantly increase the yield of single quantum dot based devices.鈥�

By using the accurate alignment, it is possible to know where the quantum dots are, allowing fabricators to pinpoint them and 鈥渦se, for instance, a pulsed laser to excite them so that they emit single photons on demand,鈥� H枚fling says. 鈥淏efore, it was guesswork. A random distribution of quantum dots would have to be used, shining light on it and hoping to find a proper located quantum dot in the device. Now, it鈥檚 much easier鈥�.

H枚fling does point out that the work needs to carry on further. 鈥淩ight now, this work addresses spatial aspects only. We know in advance where the quantum dots are, but they can still have different properties. We also need to control better their properties, namely we need additionally a spectrally deterministic technology. That is what we are working on now, but site-control can here also be very useful to manipulate the properties of the quantum dots.鈥�

Even without the spectral aspect, though, H枚fling thinks that the work done by him and his peers has the potential to be very useful in the future. He says that single photon sources, single quantum dot lasers, electron memory devices, entangled photon pair emitters and the semiconductor building blocks for quantum information processing could all advance with help from this technology.

鈥淓verything is decreasing in size,鈥� H枚fling points out, 鈥渁nd we need smaller and smaller devices. At some point, we are going to need to be able to produce single quantum dot based devices.鈥�

鈥淲e have, in the meantime, succeeded to couple a single quantum dot spatially in a spatially deterministic way with a single photonic crystal mode,鈥� he continues, 鈥測ielding a device which is capable of efficiently emitting single photons on demand.鈥�

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