Double Heterostructure GaAs Tunnel Junction for a AlGaAs/GaAs Tandem Solar Cell

Abstract

A double hetero (DH) GaAs tunnel diode which consists of a GaAs tunnel junction sandwiched between Al x Ga1-x As layers has been grown by molecular beam epitaxy, and its annealing characteristics studied. DH tunnel diodes have the advantage that a decrease in the tunnel peak current density due to annealing is greatly suppressed compared to conventional GaAs diodes without AlGaAs layers. In-depth profiles of dopants indicate that the AlGaAs layers act as blocking layers against Be diffusion, which causes a degradation of the diodes. An Al0.4Ga0.6As/GaAs tandem solar cell incorporating the DH tunnel junction as interconnectors has achieved a conversion efficiency of 20%.

Development of tunnel junctions with high peak tunneling currents for InP-based multi-junction solar cells

“…In structure 3, the modeled values for the peak tunnel current is 22.5 A/cm 2 . The InAlAs double heterostructure design improves the tunneling performance of the device, in a manner similar to studies by other authors [9,10].…”

III‐V Solar Cells

“…Secondly, actually achieving very abrupt p ++ /n ++ layers and preventing dopant diffusion during the remainder of the epitaxial growth is also challenging. One important means for preventing dopant diffusion has been the use high-bandgap materials (typically AlGaAs or AlInGaP) that act as diffusion barriers around the tunnel junction [87][88][89] as well as serving as useful window/BSF layers; for clarity these barriers are not shown in Figure 6.9.…”

The potential of III‐V semiconductors as terrestrial photovoltaic devices

“…The different cells in a MJ structure are interconnected by tunnel junctions (TJ), 58,59 thin (about 10nm) heavily doped pþ-nþ layers, which offer a low resistance to current flow. When forward biased, and below a certain current threshold, TJ behaves like a low-value resistor.…”