Like snowflakes or fingerprints, no two quantum dots are identical. But a new etching method for shaping and positioning these semiconductor nanocrystals might change that. What's more, tests at the National Institute of Standards and Technology (NIST) confirm that etched quantum dots emit single particles of light (photons), boosting prospects for powering new types of devices for quantum communications.
The conventional way to build quantum dotsat NIST and elsewhereis to grow them like crystals in a solution, but this somewhat haphazard process results in irregular shapes. The new, more precise process was developed by NIST postdoctoral researcher Varun Verma when he was a student at the University of Illinois. Verma uses electron beam lithography and etching to carve quantum dots inside a semiconductor sandwich (called a quantum well) that confines particles in two dimensions. Lithography controls the dot's size and position, while sandwich thickness and compositionas well as dot sizecan be used to tune the color of the dot's light emissions.
Some quantum dots are capable of emitting individual, isolated photons on demand, a crucial trait for quantum information systems that encode information by manipulating single photons. In new work reported in Optics Express,* NIST tests demonstrated that the lithographed and etched quantum dots do indeed work as sources of single photons. The tests were performed on dots made of indium gallium arsenide. Dots of various diameters were patterned in specific positions in square arrays. Using a laser to excite individual dots and a photon detector to analyze emissions, NIST researchers found that dots 35 nanometers (nm) wide, for instance, emitted nearly all light at a wavelength of 888.6 nm. The timing pattern indicated that the light was emitted as a train of single photons.
NIST researchers now plan to construct reflective cavities around individual etched dots to guide their lig
|Contact: Laura Ost|
National Institute of Standards and Technology (NIST)