Comments on "Bandgap of InN is 0.7 eV" story

Very recently it has been revealed that the true bandgap of hexagonal InN is about 0.7 eV, in a sharp contrast to a nearly 2 eV widely accepted and cited as a reference value in the semiconductor literature. The first conclusive evidence of a much narrower direct bandgap of InN provided by the International team of researchers from Russia, Germany, Belarus, and Japan appeared in the on-line version of our paper [1] on the website of Phys. Stat. Sol. (b) in December 2001. That short note was based on the results of theoretical and experimental extensive studies carried out by means of infrared absorption as well as photoluminescence emission and excitation spectroscopy on single-crystalline hexagonal InN layers. A well pronounced photoluminescence band at 0.75 eV to 0.85 eV, being close to the absorption edge of InN, was demonstrated for the first time. It has been shown that the measured values are in agreement with quasiparticle band-structure calculations (within their accuracy of about 0.1 eV). A large body of our experimental data obtained on In-rich In_xGa_1-xN alloys at (0.36 < x < 1) made it possible to submit a second rapid communication [2] published in the on-line version of the same journal in February 2002. All the results presented in [2] substantiated the conclusion of a narrow bandgap of InN. It should be pointed out that the both papers mentioned above were put on the website of Phys. Stat. Sol. (b) a few days after their acceptance by this journal.

In February 2002, a paper by Wu and Walukiewicz from Lawrence Berkeley National Laboratory (LBNL) and coauthors [3] also devoted to the optical properties of InN was submitted to Appl. Phys. Letters. This paper, which gave a reference to our previous communication [1], did not contradict the conclusion on a narrow bandgap of InN drawn earlier by our group.

In April 2002 the Berkeley and Cornell University groups submitted another paper [4] to Appl. Phys. Letters, treating the problem of In-rich InGaN alloys and putting the bandgap bowing parameter for these alloys determined in our communication [2] under question. However, later Hori, Kano et al. from Ritsumeikan University, Japan, [5] confirmed the correctness of our estimate of the bandgap bowing parameter for In-rich InGaN alloys given in [2].

To our great surprise, in late November 2002, Dr Walukiewicz started to dissimilate the information through the Internet site of the Berkeley Lab. in the paper titled "Full Solar Spectrum Photovoltaic Materials Identified" which essentially distorts the situation. Walukiewicz claimed that his group, in collaboration with Cornell University, USA and Ritsumeikan University, Japan "has discovered that, contrary to earlier reports, the bandgaps of the In_xGa_1-xN ternary alloys system extend over a very wide energy range (0.7 eV to 3.4 eV)". This information did not make any reference to the papers [1,2] published by us earlier.

In actual fact, the first version of the manuscript "Absorption and emission of InN: A possible revision of the fundamental gap value", which reported on our experimental findings establishing the narrow bandgap of InN and theoretical calculations, was submitted to Phys. Rev. Letters in summer of 2001 (received on 13 July 2001). Unfortunately, the evidence of narrow InN bandgap presented in the manuscript did not convince the referees of this journal.

In spite of the fact that Phys. Rev. Letters did not accept our paper, we believed that our results were correct and did not miss any opportunity to discuss them in scientific centers involved in nitride semiconductor studies. During a visit of Drs Davydov and Emtsev to the USA in early November 2001, two seminars giving exhaustive information on the latest theoretical and experimental findings obtained by our international team on InN layers and In-rich InGaN alloys and establishing a narrow bandgap of InN were given. The first seminar was arranged by Prof Haller at LBNL, and the second seminar was arranged by Prof Watkins at Lehigh University, Bethlehem, PA. Moreover, to convince our American colleagues at LBNL of the reliability of our optical measurements on InN, we demonstrated to Dr Walukiewicz's group that the photoluminescence band at 0.75 eV to 0.85 eV could easily be measured (using our InN samples and a photoluminescence facility available at LBNL). The rest of the story is given above.

Of course, we have no intention to underestimate the contribution of American colleagues, especially taking into account that Prof Haller from LBNL is a co-author of our paper [2]. However, we believe that it is important that not only the readers of printed scientific literature but also readers of Internet journals got the right information on the history of discovery of the narrow InN bandgap.

For more information please visit the Ioffe Institute website.

Yours sincerely,

Dr. V. Davydov (valery.davydov@mail.ioffe.ru), Prof. A. Klochikhin (albert.klochikhin@mail.ioffe.ru), Prof. R. Seisyan, Dr. V. Emtsev, and Dr. S. Ivanov
Ioffe Physico-Technical Institute, Russian Academy of Science, Polytechnicheskaya 26, 194021 St. Petersburg, Russia

Prof. Dr. F. Bechstedt (bechsted@j13.physik.uni-jena.de) and Dr. J. Furthmüller
Institut für Festkörpertheorie and Theoretische Optik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena, Germany

Prof. Dr. J. Graul (jgraul@lfi.uni-hannover.de) and Dipl.-phys. J. Aderhold
LfI University of Hannover, Schneiderberg 32, 30167 Hannover, Germany

Prof. A. Mudryi (mudriy@ifttp.bas-net.by)
Institute of Solid State and Semiconductor Physics, Belarus Academy of Sciences, Brovki 17, 220072 Minsk, Belarus

Prof. H. Harima (harima@dj.kit.ac.jp)
Department of Electronics and Information Science, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan

Prof. A. Yamamoto (yamamoto@fuee.fukui-u.ac.jp)
Department of Electronics Engineering, Fukui University, Bunkyo, Fukui 910-8507, Japan

References

[1] V. Yu. Davydov, A. A. Klochikhin, R. P. Seisyan, V. V. Emtsev, S. V. Ivanov, F. Bechstedt, J. Furthmüller, H. Harima, A. V. Mudryi, J. Aderhold, O. Semchinova, and J. Graul, Absorption and Emission of Hexagonal InN. Evidence of Narrow Fundamental Bandgap, phys. stat. solidi (b), 229(3), R1 (2002) (Received 18 December 2001; accepted 20 December 2001).

[2] V. Yu. Davydov, A. A. Klochikhin, V. V. Emtsev, S. V. Ivanov, V. V. Vekshin, F. Bechstedt, J. Furthmüller, H. Harima, A. V. Mudryi, A. Hashimoto, A. Yamamoto, J. Aderhold, J. Graul, and E. E. Haller, Bandgap of InN and In-rich In_xGa_1-xN alloys (0.36 < x < 1), phys. stat. solidi (b), 230(2), R4 (2002) (Received 22 February 2002; accepted 26 February 2002).

[3] J. Wu, W. Walukiewicz, K. M. Yu, J. W. Arger III, E. E. Haller, H. Lu, W. J. Schaff, Y. Saito, and Y. Nanishi, Unusual properties of the fundamental bandgap of InN, Appl. Phys. Lett. 80, 3967 (2002) (Received 14 February 2002; accepted 3 April 2002).

[4] J. Wu, W. Walukiewicz, K. M. Yu, J. W. Ager III , E. E. Haller, Hai Lu, and William J. Schaff, Small bandgap bowing in In1–xGaxN alloys, Appl. Phys. Lett. 80, 4741 (2002) (Received 3 April 2002; accepted 30 April 2002).

[5] M. Hori, K. Kano, T. Yamaguchi, Y. Saito, T. Araki, Y. Nanishi, N. Teraguchi, and A. Suzuki, Optical Properties of InxGa1-xN with Entire Alloy Composition on InN Buffer Layer Grown by RF-MBE, phys. stat. sol. (b) 234, 750 (2002) (Revised 22 July 2002; accepted 1 October 2002).