Radiation and Nitrides
Radiation Effects in Semiconductor III-Nitrides
Tech Area / Field
- MAT-SYN/Materials Synthesis and Processing/Materials
- PHY-SSP/Solid State Physics/Physics
8 Project completed
Senior Project Manager
Lapidus O V
Karpov Institute of Physical Chemistry (2), Russia, Kaluga reg., Obninsk
- State Institute of Rare Metals, Russia, Moscow
- Wright State University / Semiconductor Research Center, USA, OH, Dayton\nEuropean Materials Research Society (EMRS), France, Strasbourg\nUniversity of Florida / Department of Materials Science and Engineering, USA, FL, Gainesville
Project summaryThe aim of the proposed research is to study in detail the nature of radiation related processes in GaN, related GaN-based ternary solutions, in GaN-based heterojunctions, Schottky diodes, photodiodes and MIS structures as these processes develop in the materials irradiated by electrons, neutrons, protons. The authors also will develop practical recommendations for GaN materials science and device applications as related to the problem of radiation hardness.
It is planned to study in detail the influence of electron, proton and neutron irradiation on the charge carriers concentration and mobility and the spectra of deep centers in GaN and AlGaN. We will also study the effects of radiation on the 2D-electrons mobility and concentration and on interface traps type and density in AlGaN/GaN heterojunctions HJs. The effects of radiation on the interface states density in GaN-based MIS-structures and on the leakage currents and breakdown voltages of the AlGaN-based diodes will be investigated. We will compare the radiation effects pattern obtained on GaN-based structures with different dislocation densities to reveal the impact of dislocation on such processes. The results will be both of great practical interest as they will allow to analyze the operation of GaN photodiodes, power rectifiers and field effect transistors in hostile radiation environment and of great scientific interest as they will provide new clues for understanding the nature of radiation and native defects and their impact on electrical and recombination properties of group III-nitrides. The state of our knowledge in this area is at the present moment absolutely inadequate and this provides for the novelty of the proposed research.
It is planned that the project will be carried out by the joint efforts of two groups, the group at the Obninsk Branch of L.Y. Karpov Research Institute of Physical Chemistry (henceforward the Obninsk group) and the group at the Institute of Rare Metals (henceforth the IRM group). The Obninsk group is one of the recognized leaders in the studies of radiation defects in semiconductors and in radiation technology of semiconductors. It has many years experience in research related to radiation damage in various semiconductor materials and in radiation-induced modification of the properties of semiconductor materials, such as neutron transmutation doping of semiconductors, etc. This group has at their disposal a unique combination of irradiation techniques including a VVR-type nuclear reactor, several linear accelerators of electrons and protons, Co-60 g-ray sources and various characterization equipment including variable Hall effect measurements machine (LHe to 400 K), several optical spectrometers and Fourier spectrometers, HRXRD machines, etc. all of which will be highly instrumental in carrying out the tasks set in this project. The group has experience in working on ISTC projects. In the course of their work the group has set up a network of international cooperations that will be very helpful to the present project.
The IRM group has by now firmly established itself as one of the world leaders in the studies of the properties of wide-bandgap semiconductors, such as GaN, AlGaN, InGaN, ZnO. It was among the first to publish the results of deep level studies in GaN, AlGaN and AlGaN/GaN, GaN/InGaN, AlGaN/SiC heterojunctions, to present detailed studies of the impact of dislocations on deep levels spectra and breakdown voltages in GaN, to describe the effects of proton implantation on deep levels and recombination properties of GaN, AlGaN, ZnO, to report the properties of power rectifiers with record-high breakdown voltages in AlGaN, to study the effects of ion implantation and doping of GaN and AlGaN with transition metals impurities.The group has at its disposal several advanced DLTS spectrometers, equipment for performing C-V profiling, admittance spectroscopy, I-V measurements, MCL spectra measurements, diffusion length measurements, etc. Through its various contacts with the leading materials growth groups the group has access to all the necessary nitride materials and structures to be used in the course of this project. At the moment the group is setting up an in-house growth of GaN films by HVPE that should be up and running by the time the project is expected to start. We are also in the process of setting up the in-house MOCVD growth, hopefully to start approximately at the time of the project commencement.
Thus both groups have all the necessary equipment and expertise to carry the project to the successful end.
The work on the project will allow alternative (not defence-oriented) employment of more than 30 people, out of which 28 were previously involved in the R&D studies aimed at creating new military equipment with enhanced radiation hardness regarding both the nuclear-explosives and space radiation ambience. In addition, the work on the project will allow to switch the use of unique nuclear physics equipment created for defence research and modeling purposes and redirect it towards civilian applications such as the studies of electrical, optical and structural properties of GaN-based materials and devices. This will help to preserve the huge research potential of the Russian science and channel it to civilian purposes.
The foreign scientists that have agreed to serve as collaborators on this project show a great interest to the planned research. They are particularly interested in joint studies of radiation physics problems in group III-nitrides materials and devices, in improvement of the materials quality and their radiation hardness. They also show great interest to assessment of radiation-induced degradation of heterostructures and device structures and in finding new promising areas of radiation technology applications.
The joint research with foreign collaborators will involve intensive exchange of scientific information between the participants and extensive discussions of the quarterly and annually achieved results for particular tasks of the project and for the project as a whole. It is planned that the collaborators will participate in joint experiments. It is also planned to organize a round-Robbin process of exchange of samples and joint measurements in various participating groups in order to compare the quality of samples coming from various sources. It is expected that the foreign collaborators will be able to participate in joint workshops on the problems related to the project.
In order to achieve the goals of the present project we plan to use modern methods of studies, such as:
- Measurements of 2D-electrons mobility and concentration at room temperature and low temperatures;
- C-V profiling of the carrier concentration in single film structures and in heterojunctions; assessment of the quality of MIS structures by C-V measurements at various frequencies;
- Deep levels studies using both electrical and optical excitation and current DLTS studies with optical (PICTS) and electrical (CDLTS) injection, those will be performed also on MIS structures;
- MCL studies at room temperature and at 90 K;
- Diffusion length measurements by EBIC;
- Optical (measurements of optical absorption at 90 K and 300 K) and structural studies of GaN and AlGaN epilayers;
- Measurements of I-V characteristics, C-V characteristics, C/G-T characteristics and photoconductivity on GaN-based devices.
In order to better understand the nature of the mechanisms leading to formation and annealing of radiation defects in nitrides, interaction of these defects with native defects present in the material, the impact of these defects on the properties of GaN-based films and device structures we plan to perform theoretical calculations of the levels of deep native defects (vacancies, antisite defects) created by irradiation. The models will also take into account the influence on electronic properties and optical properties of clustered defects created by radiation. One of the aims of such theoretical work is to predict the final state achieved in GaN, AlN and related ternaries after very high doses of radiation.
The results generated in this project will allow to formulate some practical recipes for obtaining high-quality GaN-based films and devices and will serve as a basis for the future microelectronic applications.