Local photocurrent mapping of InAs/InGaAs/GaAs intermediate-band solar cells using scanning near-field optical microscopy

The near-field photocurrent mapping of InAs/InGaAs/GaAs quantum-dots intermediate-band solar cells by means of scanning near-field optical microscopy is discussed. By illumination through the InZn top contact at two different wavelengths (visible, 800nm, and near infrared, 1150nm), topography and photocurrent information were simultaneously collected. The lateral resolution was ~100nm. A strong correlation between topography and local photocurrent has been observed which is attributed to efficient photocarrier generation in intermediate-band solar cells. We found that this is due to the presence of photocarrier transfer from quantum dots to the InGaAs strain-compensated layer or to the GaAs spacer layer. Furthermore, a reduced local photocurrent was found right on top of the InAs quantum dot which has been explained by trapping of photo-generated electrons from the GaAs region by InAs quantum-dot states. The effect of the thickness of the GaAs spacer layer and the effect of Si-delta doping on topography and photocurrent distribution are also discussed.