Non‐Destructive Wafer Recycling for Low‐Cost Thin‐Film Flexible Optoelectronics

Abstract

Compound semiconductors are the basis for many of the highest performance optical and electronic devices in use today. Their widespread commercial application has, however, been limited due to the high cost of substrates. Device costs can be significantly reduced if the substrate is reused in a simple, totally non‐destructive and rapid process. Here, a method that allows the indefinite reuse and recycling of wafers is demonstrated, employing a combination of epitaxial “protection layers”, plasma cleaning techniques that return the wafers to their original, pristine, and epi‐ready condition following epitaxial layer removal, and adhesive‐free bonding to a secondary plastic substrate. The generality of this process is demonstrated by fabricating high performance GaAs‐based photovoltaic cells, light emitting diodes, and metal‐semiconductor field effect transistors that are transferred without loss of performance onto flexible and lightweight plastic substrates, and then the parent wafer is recycled for subsequent growth of additional device layers. This process potentially leads to a transformational change in device cost, arising from the inevitable consumption of the wafer that accompanies conventional epitaxial liftoff followed by chemo‐mechanical polishing.

Transforming the cost of solar-to-electrical energy conversion: Integrating thin-film GaAs solar cells with non-tracking mini-concentrators

“…9 The previously described ND-ELO method employs epitaxial protective layers grown between the sacrificial layer and the wafer that completely preserve the original wafer surface quality, even at the atomic scale, during the ELO process. 9,10 Selective removal of the protective layers using wet chemical etching eliminates the need for the chemomechanical polishing used in conventional ELO. Therefore, ND-ELO allows for the nearly indefinite reuse of the GaAs substrates, converting their cost from a material expense into a capital investment.…”

“…9,19,20 Then, the bonded sample is submerged in dilute, hot HF to lift-off etch the die in 30 min. This process takes .5 h for a 5-cm-diameter wafer using conventional ELO under similarly optimized etching conditions, corresponding to a .103 reduction in process time.…”

“…This process takes .5 h for a 5-cm-diameter wafer using conventional ELO under similarly optimized etching conditions, corresponding to a .103 reduction in process time. 9 Next, the lifted-off bars are fabricated into photovoltaic cells 9 and then separated along the trenches using a CO 2 laser scriber (see 'Materials and Methods' and Supplementary Information SI 1) with a kerf of ,300 mm.…”

“…Once the GaAs substrate fully adheres to the Kapton H sheet, the thin active device region is removed from its parent substrate using ND-ELO. 9 The sample is immersed in a 20% HF:H 2 O solution maintained at 60 6 C while …”

“…[5][6][7][8] However, the cost reduction long promised by the epitaxial lift-off (ELO) process has primarily been limited by the inability to fully recover the original wafer surface quality after each growth, leading to a limited number of times that the substrate can be recycled due to the accumulation of defects and to wafer thinning incurred by chemo-mechanical polishing. [9][10][11][12][13] Furthermore, high PCE alone does not necessarily translate into low-cost solar energy production when expensive active materials and fabrication processes are used in their manufacture. As an alternative to simply improving PCE, solar concentrators have been demonstrated as a means for reducing the use of costly active solar cell materials.…”