NIST researchers measure the single electron spectrum of InAs quantum dots.

Quantum dots (QD)--nanometer-scale semiconductor islands--are being investigated for a variety of optoelectronic applications, including use as single photon-on-demand sources. Such a source operates by tunneling a single electron and hole onto a QD where they recombine to produce a single photon. This type of single photon source would be used for new optical calibration devices and could become part of quantum communications systems.

To understand the behavior of these devices, it is necessary to measure the electrical properties of individual QDs at the single electron level. NIST researchers recently have measured the single electron spectrum of a semiconductor heterostructure containing InAs self-assembled quantum dots. In this experiment, a single electron transistor (SET) is fabricated on a semiconductor structure containing InAs QDs and an underlying n-doped GaAs layer. As the bias voltage of the n-doped layer is decreased, electrons tunnel from the n-doped layer into the neighboring quantum dots and are detected by the SET. The measurement was made possible by a new data acquisition system that cancels the linear background signal originating from the bias voltage of the n-doped layer with a balancing voltage applied to a side gate of the SET. This experiment will allow researchers to understand and control the tunneling of individual electrons into a quantum dot, and will serve as an important step toward making an electrically controlled single-photon source.

CONTACT: Kevin Osborn, [phone]; [e-mail].