Epitaxial Lift‐Off for large area thin film III/V devices

Abstract

The present work describes the study and improvement of the Epitaxial Lift-Off (ELO) technique, which is used to separate III/V device structures from their GaAs substrates. As a result the ELO method, initially able to separate millimetre sized GaAs layers with a lateral etch rate of about 0.3 mm/h, has been developed to a process capable to free entire 2″ epitaxial structures from their substrates with etch rates up to 30 mm/h. It is shown that with the right deposition and ELO strategy, the thin-film III/V structures can be adequately processed on both sides. In this way semi-transparent, bifacial solar cells on glass were produced with a total area efficiency in excess of 20% upon front side illumination and more than 15% upon back side illumination. The cell characteristics indicate that, once the thin film processing has been optimized, ELO cells require a significantly thinner base layer than regular III/V cells on a GaAs substrate and at the same time have the potential to reach a higher efficiency.

Epitaxial lift-off process for gallium arsenide substrate reuse and flexible electronics

“…The attack of the substrate by the HF and the residues formed during the sacrificial layer etching result in the increase of RMS roughness from 0.3 to 1-4 nms range. Chemical reactions between AlAs and HF have been well studied 10,15,16 6 À n ] (3 À n) þ , on the other hand, are solid and hard to dissolve into the solution. Besides these primary byproducts, solid As 2 O 3 can also be generated on the substrate depending on the oxygen concentration of the etchant 17 .…”

“…Performing the ELO process in the chemical reaction rate limited regime is preferred as it can maximize the overall etch rate. In order to do so, several methods with sophisticated setups, for example, weight-assisted ELO 30 and etching assisted by roller 15,31 , were developed to accelerate the ELO process. However, these are only single-wafer solutions with consequent low throughput.…”

Environmental impact of thin-film GaInP/GaAs and multicrystalline silicon solar modules produced with solar electricity

“…Fulltime operation of the reactor system corresponds to an annual production capacity of approximately 0.1 MW p . By means of an advanced epitaxial lift-off (ELO) technique, the solar cell is separated from the GaAs wafer (Schermer et al 2005); the technique is assumed to allow for 95% reuse of this wafer. A solar energy conversion efficiency of the thin-film GaInP/GaAs cell of 28.5% is considered (Mohr et al 2007).…”

The potential of III‐V semiconductors as terrestrial photovoltaic devices

“…Finally, in order to save on substrate costs of III-V cells, it is possible to remove the substrate from the epilayer by a lift off process [94][95][96] and reuse it for successive growths. The epifilm can be bonded to a foreign substrate, in order to get mechanical support and both electrical and thermal conductivity.…”