High current density tunnel diodes for multi-junction photovoltaic devices on InP substrates

Abstract

InAlGaAs tunnel diodes, lattice-matched to InP and grown by molecular beam epitaxy, are demonstrated with peak tunneling current densities exceeding 1200 A/cm2. This was achieved by a 20 °C reduction in growth temperature for the p-type tunnel diode layers, resulting in up to two orders of magnitude improvement in the peak tunneling current density. Secondary ion mass spectrometry measurements reveal that the lower growth temperature reduces unwanted segregation of p-type Be dopants, improving dopant incorporation within the active tunnel diode layers. The diodes are transparent to wavelengths above 1000 nm and are compatible with the bottom junctions of InP-based multi-junction solar cells and with InP-based photonic power converters operating in the telecommunication O- A nd C-bands. When incorporated into a dual-junction photonic power converter test structure, measurements under 1319-nm laser illumination demonstrate integrated tunnel diode operation, enabling a halving of the short-circuit current and doubling of the open-circuit voltage as compared to a single junction reference device.