The development of (InGa)As thermophotovoltaic cells on InP using strain-relaxed In(PAs) buffers

We have investigated thermophotovoltaic monolithic interconnected modules fabricated from In0.68Ga0.32As on InP using In(PAs) buffer layers to mitigate the lattice mismatch. The growth of these devices presented several challenges. For example, the n-type dopant Te forms a persistent surface-segregation layer on In(PAs) and (InGa)As layers, which unintentionally distributes Te into subsequently deposited layers. To solve this problem, we identified growth conditions that promote Te desorption from the InGaAs surface, thereby enabling the formation of sharp doping profiles. Another significant challenge involved In-rich surface defects, which form during In0.68Ga0.32As growth and act as shunt paths that severely reduce cell performance. To address this problem, we implemented pre-growth particle-control procedures that allow surface defect densities below 100 cm−2 to be obtained. Our progress allowed the demonstration of thermophotovoltaic cells producing 348 mV/junction open-circuit voltage with a fill factor exceeding 70%.