UC San Diego

Flexible substrates have many advantages in applications where bendability, space, or weight play important roles or where rigid circuits are undesirable. However, conventional flexible thin film transistors are typically characterized as having low carrier mobility as compared to devices used in the electronics industry. This is in part due to the limited temperature tolerance of plastic flexible substrates, which commonly reduces the highest processing temperature to below 200°C. Common approaches of implementation include low temperature deposition of organic, amorphous, or polycrystalline semiconductors, all of which result in carrier mobility well below 100 cm²V⁻¹s⁻¹. High quality, single crystalline III-V semiconductors such as indium phosphide (InP), on the other hand, have carrier mobility well over 1000 cm²V⁻¹s⁻¹ at room temperature, depending on carrier concentration. Recently, the ion-cut process has been used in conjunction with wafer bonding to integrate thin layers of III-V material onto silicon for optoelectronic applications. This approach has the advantage of high scalability, reusability of the initial III-V substrate, and the ability to tailor the location (depth) of the layer splitting. However, the transferred substrate usually suffers from hydrogen implantation damage. This dissertation demonstrates a new approach to enable integration of InP with various substrates, called the double-flip transfer process. The process combines ion- cutting with adhesive bonding. The problem of hydrogen implantation was overcome by patterned ion-cut transfer. In this type of transfer, areas of interest are shielded from implantation but still transferred by surrounding implanted regions. We found that patterned ion-cut transfer is strongly dependent upon crystal orientation and that using cleavage-plane oriented donors can be beneficial in transferring large areas of high quality semiconductor material. InP-based devices were fabricated to demonstrate the transfer process and test functionality following transfer. Passive devices (photodetectors) as well as active transistors were transferred and fabricated on various substrates. The transferred device layers were either implanted through with a blanket implant or protected with an ion-mask during implantation. Results demonstrate the viability of the double-flip ion-cut process in achieving very high electron mobility (2̃800 cm²V⁻¹s⁻¹) transistors on plastic flexible substrates