Single‐junction InGaP/GaAs solar cells grown on Si substrates with SiGe buffer layers

Abstract

Single junction InGaP/GaAs solar cells displaying high efficiency and record high open‐circuit voltage values have been grown by metal–organic chemical vapor deposition on Ge/graded SiGe/Si substrates. Open‐circuit voltages of 980 mV under AM0 conditions have been verified to result from a single GaAs junction, with no evidence of Ge‐related sub‐cell photoresponse. AM0 efficiencies close to 16% have been measured for a large number of small‐area cells, the performance of which is limited by non‐fundamental current losses due to significant surface reflection resulting from> 10% front‐surface metal coverage and wafer handling during the growth sequence for these prototype cells. It is shown that at the material quality currently achieved for GaAs grown on Ge/SiGe/Si substrates, namely a 10 ns minority‐carrier lifetime that results from complete elimination of anti‐phase domains, and maintaining a threading dislocation density of ∼8 × 105 cm−2, 19–20% AM0 single‐junction GaAs cells are imminent. Experiments show that the high performance is not degraded for larger‐area cells, with identical open‐circuit voltages and higher short‐circuit current (due to reduced front metal coverage) values being demonstrated, indicating that large‐area scaling is possible in the near term. Comparison with a simple model indicates that the voltage output of these GaAs‐on‐Si cells follows the ideal behavior expected for lattice‐mismatched devices, demonstrating that unaccounted‐for defects and issues that have plagued other methods to epitaxially integrate III–V cells with Si are resolved by using SiGe buffers and proper GaAs nucleation methods. These early results already show the enormous and realistic potential of the virtual SiGe substrate approach for generating high‐efficiency, lightweight and strong III–V solar cells. Copyright © 2002 John Wiley & Sons, Ltd.

III-V Device Integration on Silicon Via Metamorphic SiGe Substrates

“…This yields efficiencies for GaAs/SiGe/Si of 18.8% and 16.5% at AM1.5-G and AM0, respectively, more than 1% absolute higher than other verified reports (18)(19)(20).…”

Heterojunction Diodes and Solar Cells Fabricated by Sputtering of GaAs on Single Crystalline Si

“…Furthermore, graded SiGe layers, prepared by chemical vapor deposition (CVD), molecular beam epitaxy (MBE) or low-energy plasma enhanced CVD (PECVD), were used as buffers between Si and GaAs in order to reduce the lattice mismatch [9][10][11][12][13].…”

The potential of III‐V semiconductors as terrestrial photovoltaic devices

“…Since the 80s, III-V Si heteroepitaxy has been the 'Holy Grail' of the whole semiconductor industry: the growth of GaAs on Si, if successful, will allow a strong cost reduction and integration of fast electronic and optical devices on Si. There are several research groups involved in developing methods for growing GaAs over Si: in the past years, several III-V devices have been realised on Si substrates, including single junction GaAs solar cells, 83 GaAs LEDs 84 and InGaAs laser diodes. 85 A lot of efforts are currently being made in developing a reliable heteroepitaxy method for the deposition of GaAs/Si.…”