Heterointegration of compound III-V semiconductors by wafer bonding and layer splitting for optoelectronic applications

In recent years, the use of III-V nitride compound semiconductors such as GaN, AlN, and InN has seen a rapid growth in the optoelectronics industry. Due to the efficient emission of light based on their direct bandgap several compound semiconductors are attractive for hybrid devices for optoelectronic and photovoltaic applications. It is widely acknowledged that the exploitation of the full potential of these emerging technologies is held back primarily by the high cost of prime grade crystalline quality material and the relative small wafer diameters available. On top of these challenges commercially available epitaxial samples suffer from high defectivity, because of the large lattice mismatch between these semiconductors and the commonly used sapphire substrate. In this context wafer bonding provides an alternative approach to integrate dissimilar material systems with superior crystal quality devoid of epitaxial lattice defects and at reasonable cost. The heterogeneous integration process combines semiconductor wafer bonding technology with the ion cutting process by hydrogen implantation in order to achieve novel composite material systems that are unattainable by conventional epitaxy techniques¹. One of the possibilities to reduce the material cost would be the application of the ion-cut process to cleave several thin layers from the same wafer and their transfer onto foreign and cheap substrates. In principle, this ion-cut, a generic process based on light ion (using H or He) implantation and wafer bonding, can be used to transfer bulk quality fine layers onto foreign substrates thereby achieving heterostructures frequently unattainable by other methods such as epitaxy. The transfer of several layers from the initial starting wafer affords a significant reduction of the material cost. Avoiding conventional epitaxy techniques with their inherent lattice mismatch challenges when marrying dissimilar semiconductor materials constitutes a major advanta- e for the wafer bonding and layer transfer technology. There are two approaches to affect the bonding of dissimilar materials. In the first approach the wafers are directly bonded without the use of an intermediate layer. In the second case bonding is achieved via an intermediate layer, which is a dielectric layer in most applications. Following successful bonding of dissimilar materials the heterointegration process will be completed by release of a thin layer of the III-V semiconductor. The release and transfer of such thin layers to foreign substrates is accomplished by cleaving ion implanted III-V samples. The state-of-the-art technique is to implant, the compound semiconductor samples by H or He energetic ions to create a mechanically weak zone a below the surface of the donor wafer². The influence of the implant fluence, the post implant annealing conditions required for the layer transfer and the resulting material modifications weakening the cleavage zone will be reviewed. Systematic studies of the influence of thermal treatment and implant dose on cleavage behavior have been performed with high resolution TEM cross-sectional analysis combined with other relevant physical characterization techniques³. Fig. 1 displays the example of AlN, where the hardness increases with annealing temperature rendering the III-V material more brittle. This presentation provides new insights in the mechanical behavior of hydrogen implanted III-V semiconductors throughout subsurface microcracking leading to thin film transfer following heterogeneous wafer bonding.