Frame-assisted membrane transfer for large area optoelectronic devices on flexible substrates

Abstract

Frame assisted membrane transfer process was developed to transfer large area crystalline semiconductor nanomembranes on flexible plastic substrates. InP nanomembranes as large as 2cm×2cm was transferred successfully. Large area flexible photodetectors, solar cells and LED arrays all have been demonstrated experimentally, based on transferred InP nanomembranes.Flexible optoelectronics devices based on single crystal semiconductor nanomembranes (NM), which combine the advantages of high quality single crystalline semiconductors, with the flexibility property, are highly desirable for a wide range of applications from flexible imaging/displays, sensors, solar cells and conformal electronic/photonic integrated systems, to potential integration into artificial muscles or biological tissues. High quality single crystalline silicon NMs have been transferred onto various foreign substrates, such as glass, flexible PET (polyethylene terephthalate) plastics, etc., based on low temperature transfer and stacking processes. [1][2][3][4][5][6][7] However, two significant challenges remain in realizing practical large-area photonic devices based on stacked crystalline semiconductor NMs. The first one is the reliable transfer of large-area crystalline semiconductor NMs, especially for the fragile materials systems (e.g. GaAs, InP compound semiconductors). The second challenge is the incorporation of metal contacts for the desired electrical properties of photonic devices. Here we developed frame assisted membrane transfer (FAMT) process to address these two challenges [8]. Large area flexible InP photodetectors (PD) and solar cells were demonstrated experimentally based on this FAMT process. Similarly, we have also demonstrated flexible InP LED arrays based on substrate removal transfer processes.Shown in Fig. 1 are the schematics of FAMT process for InP NMs. The starting material is a p-i-n InP layer (total thickness of 1 μm) grown on top of an InP substrate, with an InGaAs sacrificial layer sandwiched in between. Release holes were formed first on the top InP layer, followed by Au finger contact formation. Due to the weak mechanical properties of InP, it is a significant challenge to transfer larger-area InP NMs without any other supporting structures. The Au finger contacts here serve as the device electrodes, as well as the frame to offer the desired mechanical strength for the successful transfer of large area InP NMs. Shown in Fig. 2(a) and 2(b) are pictures and micro-graphs of the InP NMs transferred on ITO/PET substrates. Very high quality 3 mm x3 mm InP NM was successfully transferred. Note the size of NMs is mostly limited by the size of photomask patterns used here. Shown in Fig. 2(c) is a transferred crystalline InP NM on PET substrate, with the size as large as 2 cm x2 cm. The suspended NM during transfer process is shown in Fig. 2(d).Large area flexible photodetectors, solar cells and LED arrays all have been demonstrated experimentally, as shown in Fig. 3, based on transferred InP nanomembranes. The measured flex...