Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - Zoterac (Zinc Oxide For TeraHertz Cascade Devices)

Teaser

Why Zoterac?The terahertz (THz) spectral region, located between the infrared and the microwave regions, is known as “the THz gap” because of the lack of compact semiconductor devices. This spectral domain is currently intensively explored in view of its potential for...

Summary

Why Zoterac?
The terahertz (THz) spectral region, located between the infrared and the microwave regions, is known as “the THz gap” because of the lack of compact semiconductor devices. This spectral domain is currently intensively explored in view of its potential for medical diagnostics, security screening, trace molecule sensing, astronomical detection, space-borne imaging, non-invasive quality control or wireless communications. A prerequisite for public-domain applications to emerge in the strategic THz frequency range is the availability of compact size semiconductor sources operating at room temperature, which is out of range of the current technology based on GaAs quantum cascade lasers.

What is Zoterac?
ZOTERAC is a project which proposes a disruptive approach based on ZnO-based nano-engineered semiconductors in order to realize THz emitters operating at room-temperature with milliWatt output power capability as well as THz quantum detectors with unprecedented large operating temperatures. These devices are based on the quantum cascade concept and take benefit of the large optical phonon energy of ZnO (twice that of GaAs) for achieving high temperature operation.

Benefits of Zoterac
Establishing a new state-of-the-art for the design, growth and processing of ZnO/ZnMgO heterostructures, and developing an advanced know-how on oxide-based devices are major challenges of the project. The consortium regroups world–class academic experts on ZnO technologies, quantum cascade lasers and detectors as well as THz optoelectronics. The strategies have been chosen based on a careful assessment of the risk attached to all tasks and achievement of targeted objectives at each stage of the project. This project which implies a strong expertize in basic physics, chemistry and engineering, is expected to generate high impacts in terms of scientific and technological achievements.

Work performed

During this period, all partners have started their activities within ZOTERAC. The planned tasks have been launched following the description of action of the GA. The scientific deliverables for the reporting period have been met, while the two milestones achieved. The work of each package has followed the planning and yielded the significant progress.

• WP1 work has been focused on the definition of reliable models. Several methods have been used (ab-initio, Schrodinger Poisson method and kp method) depending on the parameters to calculate. The task related to the QCD and QCL designs has been started and first designs have been defined although it was not anticipated during this reporting period.

• The work on the growth of the ZnO/(Zn,Mg)O quantum structures has been carried out in WP2. 85 samples have been delivered to the different partners for characterization. A methodology to quickly and precisely assess the thicknesses and the barrier composition has been developed. The new MBE system has been installed and is fully operational, delivering its first samples for the consortium.

• WP3 work has been focused on the process for the samples. The ZnO polishing has been developed to prepare samples for absorption characterization (WP4). Different etching methods have been evaluated (RIE, wet etching), while the electrical contacts and surface passivation have been investigated. Finally, resonant tunnel structures have been processed as test structures.

• At this stage of the project the main task of WP4 is to define and to measure the unknown physical parameters for ZnO and (Zn,Mg)O and to give a feedback to WP1. The samples grown in WP2 have been investigated in WP4 by different several partners in different wavelength ranges. The main striking results are (1) the observation of intersubband absorption in nonpolar ZnO/(Zn,Mg)O QWs grown on m-plane ZnO for the first time, (2) the assessment and accurate calculation of the depolarization shift of ZnO/(Zn,Mg)O intersubband transitions, (3) the estimation of the conduction band offset of non polar ZnO/(Zn,Mg)O heterostructures (4) the assessment of polaron effects on the intersubband energy.

Finally defining the visual identity of ZOTERAC and the website was the important task of WP5 during this period.

Final results

ZOTERAC will have a strategic impact for European research and will offer a world leadership in the very attractive field of the THz. The ZOTERAC objectives address directly the H2020 FET-open call by exploring novel fundamental physics, by developing a future and emerging technology, and by offering large interdisciplinary prospective.

a) Scientific and Societal Impacts

In addition to the large scientific impact directly related to the project, the THz emitters and detectors developed in ZOTERAC will generate a great breakthrough in a variety of application domains. Among them, one could retain the following striking examples:

- Since many materials (clothes, paper, plastic, walls,…) are transparent to the THz, these radiations can be employed for the detection of hidden weapons and to detect traces of explosives having absorption lines in the THz range. THz technology represents the most suitable candidate for fabricating systems in the field of security, such as people and luggage scanners in airports and other public places.
- THz radiations are non-ionizing and eye safe, they could partially replace the X-ray in medical diagnostics. In particular, the detection of skin and breast cancers will be at a so early stage that it will considerably increase the success probability of the treatment. The very high sensitivity of enamel and dentine properties to THz radiations is calling for the use in dental screening.
- From an environmental point of view, gas phase spectroscopy at THz frequencies allows to study the chemical processes in the upper atmosphere (atmospheric molecules like water, oxygen, carbon monoxide,... have strong absorption bands in this frequency range), which are crucial in ozone formation and destruction.
- The THz radiations will become at the center of material science, industrial quality control and product inspection because it represents a non-destructive technique to inspect plastics, polymers, ceramics... For instance, the pharmaceutical industry is very demanding for non-destructive and chemical analysis of tablets, capsules and other dosage forms.
- Astrophysics and space-science were the first communities to push for the achievement of efficient THz devices due to possibility of detection of interstellar oxygen (OI) with its fine structure line at 4.745 THz.

b) Economic Impact

Today, development in the optoelectronic sectors is still predominant as further improvements are needed before assessing the societal needs. These innovations rely on new device structures and novel material systems. The impact of the exceptional ZnO properties has not yet been exploited. It offers completely new opportunities for the establishment of the future THz device generation. Combining efficiency and room-temperature operation while keeping the compact-size and the low-cost requirements of the market will represent a huge breakthrough. Despite the large panel of applications, the THz domain is still largely limited by the current device limitations, and the global THz market represents only 34 M€ in 2012. Nevertheless, based on reasonable technology progress predictions, several market studies expect a THz market reaching 350–550 M€ in 2020 with an annual growth rate of 25–40% (Photonics21.org-Tematys, bbcresearch.com-IAS029A).

c) European added value and leadership

Throughout ZOTERAC, significant new scientific results and technological breakthroughs are expected. While the crucial key points of this new knowledge will be protected via patent filing, most of the how-know developed during the project will be disseminated to the wider academic, scientific, and industrial communities fostering the European research at the highest international level. Moreover, the European companies already involved in quantum cascade device technology (Alpes Laser, III-V Lab, Cascade,..) and in the THz domain (QMC instruments, Ekspla Lasers,...) will benefit from the development of this unique new THz technology to seriously compete with out-of-Europe rivals (Northwestern University, Riken, Raytheon, or Thorlabs for quantum cascade device and Gentec-EO or TeraSense for THz device manufacturers).