Wide Bandgap Semiconductor Materials and Devices

The research interest of our group is in the field of advanced electron devices based on compound semiconductors and nanotechnology. By “advanced”, we understand the use of radically new concepts and a multidisciplinary approach to both improve already existing devices and to fabricate completely new semiconductor-based micro- and nano-systems. These devices will help the introduction of Electrical Engineering in numerous new fields, including its next frontier, its interaction with biological systems.

Electrical Engineering is at a crossroads. In the last half century, electronics has driven the development of information technology that has completely changed our society. This development has been possible mainly due to the integration of devices like transistors, light emitting diodes, lasers and detectors with advanced design methodologies and parallelism. In spite of the wide breadth of these devices, all of them are based on few key concepts of semiconductor physics: channel modulation by field effect, depletion regions, carrier recombination, drift-diffusion transport, etc. Our group firmly believes that after more than 50 years of semiconductor technology development, if we want semiconductor devices to keep changing the society as they have done in the past century, it is not longer enough an evolutionary approach based on these concepts in combination with improved technology and better material quality. We need to adopt a multidisciplinary effort that uses the tools provided by areas like nanotechnology and biotechnology in conjunction with standard semiconductor physics, processing and material growth. Only with this approach will radical improvements in performance - as well as new devices - come out to push information technology well into the 21st century.

Since 1998, we have been involved with various micro- and opto-electronic devices fabricated in different semiconductor material systems. Out of all of these systems, nitride-based semiconductors have a unique combination of properties that make them especially suitable for many of the new challenges and applications of the 21st century.This material system is characterized by a wide range of very interesting properties, which make it the most complete semiconductor family. Some of these properties are: a direct bandgap tunable from 6.2 eV (AlN) down to 0.6 eV (InN), piezoelectricity, polarization, large breakdown voltage, biocompatibility, high chemical and thermal stability, etc. Moreover, even superconductivity and ferromagnetism have been proposed by some researchers. This vast array of properties make these semiconductors ideal for many applications, including LEDs and lasers, photodetectors, transistors, piezoelectric filters, biosensors, etc.

For the last 40 years, most semiconductor devices have been based in the use of a single property of a given semiconductor family. In this way, we find devices (e.g. transistors) that use the electronic properties of some materials; other devices (e.g. lasers and LEDs), on the other hand, use the optoelectronic characteristics, etc. However, there are very few devices (if any) that combine two or more of these properties in the same device (i.e. piezoelectric properties with electrical properties, or optoelectronic properties with electical properties). In our group, we believe that the future of semiconductor devices lies in the new functionality that can be obtained from the combination of semiconductor properties which have not been used together until now. From this point of view, nitrides have the potential to radically change traditional semiconductor devices by its unique ability to combine outstanding mechanical properties with excellent electronic and optoelectronic performance.

In all these research areas, we try to cover all the major steps of device engineering. In this way, our students have the opportunity to learn about all these different steps. For example, from their work in the cleanroom they learn a lot about semiconductor technology; the use of custom-made and commercial simulation packages like ADS or ATLAS gives them a deep understanding about the working principles of these devices; finally, they also have access to state-of-the-art DC and high frequency measurement labs to test the devices and compare the results with the simulations. We try to combine the development of state-of-the-art devices with a broad education in all the important fields of device engineering. We also put an important emphasis on collaborations with companies and universities in the US and abroad. This is, we believe, the best way to compete in the global environment in which we are today.