CHINESE JOURNAL OF PHYSICS VOL. 42, NO. 5 OCTOBER 2004 Microwave-Modulated Shubnikov-de Haas-like Oscillations in an Al 0.4 Ga 0.6 N/GaN Electron System J. R. Juang, 1 D. R. Hang, 2, 3 Ming-Gu Lin, 1 Tsai-Yu Huang, 1 Gil-Ho Kim, 4 C.-T. Liang, 1, * Y. F. Chen, 1 W. K. Hung, 5 Woon-Ho Seo, 4 Yoonseok Lee, 4 and Jung-Hee Lee 6 1 Department of Physics, National Taiwan University, Taipei 106, Taiwan 2 Department of Materials Science and Optoelectronic Engineering, National Sun Yat-sen University, Kaohsiung 804, Taiwan 3 Institute of Materials Science and Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan 4 Department of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 440-760, Korea 5 Department of Electro-optical Engineering, National Taipei University of Technology, Taipei, Taiwan 6 School of Electronic and Electrical Engineering, Kyungpook National University, Taegu 702-701, Korea (Received November 6, 2003) We report on measurements of the microwave-modulated Shubnikov-de Haas (SdH)-like oscillations in a GaN/AlGaN heterostructure. This technique greatly enhances the visibility of the SdH-like oscillations while keeping the carrier density constant. The enhanced SdH pattern is attributed to the hot electron effect. We find that the amplitudes of the SdH-like oscillations increase with increasing microwave power. In our case, the logarithm of the SdH- like amplitudes is proportional to the inverse of the applied perpendicular magnetic field, with striking similarity to a conventional Dingle plot. Moreover, the slopes of the Dingle- like plots are approximately constant at different applied microwave powers. However, in our case, during the microwave pulse the electrons possess an equivalent temperature higher than the lattice temperature. After the end of the microwave pulse the electrons relax to the lattice temperature. Therefore the electron temperature is not constant over the whole measurement range. Thus our new experimental results point to a deficiency in the existing theory and the urgent need for further theoretical studies on electron transport in the presence of microwave modulation. PACS numbers: 72.20.-i I. INTRODUCTION Recent efforts in developing the III-V nitride family, such as InN, GaN, and AlN, have led to significant progress in improving the material quality. There has been growing interest in heterostructures and alloys based on these nitride materials. In particular, the AlGaN/GaN heterostructure has attracted a great deal of attention due to its unique ma- terial and electronic properties [1–4]. For example, there is a high sheet electron density layer at the interface of a nominally undoped AlGaN/GaN heterostructure. This is due to http://PSROC.phys.ntu.edu.tw/cjp 629 c  2004 THE PHYSICAL SOCIETY OF THE REPUBLIC OF CHINA