Growth and characterization of buried GaSb p‐n junctions for photovoltaic applications

Abstract

Structures composed of a p(++)(Zn) GaAs layer deposited by MOVPE on a n(Te)-doped GaSb substrate were fabricated, with the purpose of obtaining GaSb p-n homo-junctions, through the diffusion of Zn into the substrate, for photovoltaic applications. Different Zn doping levels and post-growth annealing parameters were investigated. The junctions were characterized from the electrical point of view by I-V measurements, while Zn diffusion profiles were studied by SIMS analysis. The effective achievement of a GaSb buried junction, whose profile is characterized by a limited Zn diffusion into the substrate, was evidenced. Efficiency measurements by a solar simulator on 5x5 mm(2) samples were also performed in order to investigate the photovoltaic properties of the structur

Electrical characterization of a buried GaSb p‐n junction controlled by native defects

“…To this aim, both different Zn doping levels in the range 1 × 10 19 < [Zn] < 1 × 10 20 cm −3 , and time‐temperature annealing conditions, from 0 to 4 hours and from 600° to 660 °C, have been investigated with the purpose to control the depth of the junction. However, surprisingly, the penetration depth of the Zn acceptors resulted to be in the range of 50–100 nm, much lower than the typical values obtained by the common diffusion methods applied in TPV devices and practically independent of the post grown annealing processes, as shown by secondary ion mass spectroscopy (SIMS) analysis . In addition, the p‐n junction resulted located more deeply with respect to the Zn diffusion front, as pointed out by electron beam induced current (EBIC) investigation .…”

“…Therefore the market penetration of stacked cells remains limited. Recently, the fabrication of a relatively simple monolithic tandem PV cell has been suggested, stacking a bottom GaSb cell and a GaAs top cell . This attempt has an intrinsic degree of novelty due to the exploration of the GaAs‐on‐GaSb epitaxial deposition.…”

Admittance spectroscopy on buried GaSb junctions due to defect distribution in GaAs/GaSb metalorganic vapor phase epitaxy heterostructures

“…These data show the rectifying properties of the investigated samples and demonstrate that a p-n homojunction was formed in the GaSb as a consequence of the Zndoped GaAs epitaxial growth; some details of the I-V curves were discussed in previous works. 9,21 The low temperature data have been interpreted as controlled by tunneling via a band of energies lying inside the band gap, while at high temperatures, the transport has been suggested to be dominated by generation-recombination mechanisms, the first mechanism being dominant for the higher Zn doping levels.…”

“…Only a few works have been devoted either to the study of such interface 8 or to the fabrication of preliminary monolithic tandem cells. 9 High-efficiency MJ photovoltaic devices based on GaSb have been obtained by making mechanically stacked GaSb/GaAs solar cells. 10,11 A diffusion technique 12-14 may be used to fabricate p-n homojunctions in GaSb single crystals, whereas more abrupt p-n interfaces can be obtained through epitaxial deposition.…”

“…The p-type dopant was supplied through the epitaxial deposition of a heavily Zn-doped GaAs layer on the substrates. These structures were finalized to develop devices for TPV and/or all-GaAs layer based photovoltaic applications, where the bulk GaSb homojunction works as bottom cell; 9 however, in the present study, the attention is focused on the electrical properties of the GaSb junction only. Several structural and electrical investigations 19,21 confirmed the build-up of buried junctions within GaSb, with satisfying rectifying properties.…”