Onset of Quantum-Confined Stark Effects in Multijunction Photovoltaic Laser Power Converters Designed with Thin Subcells

Photovoltaic multijunction power-converting III-V semiconductor devices generate electrical power from the optical energy of laser beams. They exhibit conversion efficiencies reaching values greater than 60% and 50% for the GaAs and the InP material systems, respectively. The applications of optical wireless power transmission and power-over-fiber greatly benefit from employing such laser power converters constructed with multiple subcells; each is designed with either thin GaAs or InGaAs absorber regions. This study elucidates how the application of electric fields on thin heterostructures can create specific current-voltage characteristics due to modifications of the absorption characteristics from Franz-Keldysh perturbations and the onset of quantum-confined Stark effects. Negative differential photocurrent behavior can be observed as the reverse bias voltage is increased, until the corresponding current-clamping subcell reaches its reverse breakdown condition. The reverse voltage breakdown characteristics of the subcells were also measured to depend on the thickness of the subcell and on the optical intensity. The onset of the reverse breakdown was found to be at similar to 2.0-2.5 V under illumination and the thinner subcells exhibited higher levels of reverse bias currents. These effects can produce distinctive current-voltage behavior under spectrally detuned operations affecting the thinner subcells' biases, but have no significant impact on the performance and maximum power point of multijunction power converters.