Probing the dark exciton states of a single quantum dot using photocurrent spectroscopy in magnetic fields

We report on high-resolution photoluminescence (PL) and photocurrent (PC) spectroscopies of a single self-assembled InAs/GaAs quantum dot (QD) embedded in an n-i-Schottky device with an applied magnetic field in Faraday and Voigt geometries. The single-QD PC spectrum of neutral exciton (X$^0$) is obtained by sweeping the bias-dependent X$^0$ transition energy to achieve resonance with a fixed narrow-bandwidth laser through quantum-confined Stark effect. With a magnetic field applied in Faraday geometry, the diamagnetic effect and the Zeeman splitting of X$^0$ are observed both in PL and PC spectra. When the magnetic field is applied in Voigt geometry, the mixture of bright and dark states results in an observation of dark exciton states, which are confirmed by the polarization-resolved PL and PC spectra.