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Virtual GaN substrates on Si wafers

Fragmentation of Technology Platforms

Semiconductor - based integrated circuits (IC`s) are build up to nowadays on monolithic crystalline material. As the properties of the materials are important for the performance of the electronic circuitry, different semiconductor materials became the technology platform of choice for the various, targeted applications. Si technology is the dominant semiconductor market driven by the thirst for digital processing capability. In optoelectronic applications near the 870 nm wavelength, however, the AlGaAs alloy system on GaAs is widely employed. And for telecommunications, InP substrates became the bulk semiconductor platform, as InGaAsP can be grown lattice matched to achieve the desired 1.3 and 1.55 µm wavelength emission required for low-loss transmission in optical fibers. Today, Si and III-V (as well as the upcoming II-VI) semiconductor worlds rarely intermix due to this separation of substrate platforms.


The aim of engineered wafer systems in combination with hybrid device concepts is to increase the functionality and / or performance of integrated circuits by overcoming these limitations of electronic systems, brought about by the separation of the different semiconductor substrate platforms [8]. The main objective in the field is certainly the monolithic integration of lattice matched or mismatched alternative semiconductor thin film materials on the mainstream Si platform, as the latter is the most mature and in consequence the commercially most dominant technology. A high number of SoC solutions (e.g. III-V / Si photonics) would certainly be triggered by the successful integration of alternative semiconductor materials into sophisticated silicon or strained silicon chips. To taste the flavour of the exciting new opportunities ahead, the vision of the monolithic integration of GaAs on Si is used as an example to briefly sketch typical advantages [8]: 


  • the integrated materials system is an active circuit element by itself  

Example: GaAs based optoelectronics coupled to Si based signal processing


  • the integrated materials system serves as a buffer layer                        ˛

Example: GaAs buffer to integrate InSb based IR detectors 


  • exploit mature Si wafer technology                                                             

Example: GaAs wafers are in comparison to Si wafers limited in size


  • best combination of mechanical, electrical, thermal & processing properties 

Example: GaAs has lower thermal conductivity & mechanical stability than Si


  • film properties differ by interface, strain & quantum size effects from bulk     

Example: quantum size effects in thin GaAs layers 



A lot of R&D work was devoted to the tricky problem of combining the best attributes of compound semiconductors, like high mobility and direct band gap, with the low-cost, mature manufacturing processes of Si CMOS technologies, achieving outstanding integration levels. These efforts have brought impressive success at the research level, but in many cases commercialization of hybrid devices is still a challenge. However, as more and more aggressively scaled Si IC solutions are limited by cost explosions and fundamental material properties, worldwide R&D activities on engineered wafer and hybrid device approaches are intensified, resulting in important innovations in the field.


In the special case of virtual GaN substrates, progress is not only driven by Si IC industry for information and communication needs but also by other challenges in modern society: Here, the availability of a low-cost GaN substrate platform of high quality and reliability is of central interest to enable:


  • solid-state lighting applications for energy saving,
  • advanced blue laser technologies for modern infotainment technologies,  
  • high power, high frequency GaN electronics with high temperature stability.


As these tasks require mainly global GaN integration over the whole substrate wafer, established Si wafer companies like Siltronic AG (http://www.siltronic.com) or start-ups in the substrate product market like AZZURRO (http://www.azzurro-semiconductors.com/) are here the major drivers.



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