0741-3106 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LED.2017.2720480, IEEE Electron Device Letters 1 Abstract—We study the potential and feasibility of high hole mobility transistors (HHMTs) based on flexible AlGaInN/GaN heterostructures using numerical simulation. We develop a map for the sheet density of two-dimensional hole gas (2DHG) at different mole fractions of AlN, GaN, and InN of AlGaInN with mechanical bending conditions. External compressive strain via bending can induce relatively high density of 2DHG (e.g., > 8×10 12 cm -2 ) while keeping InN fraction low (<0.3) so that 2DHG channel can be formed in a GaN layer. We show the electronic energy band diagrams, family curves of I-V characteristics, and transfer characteristics of an In 0.25 Al 0.75 N/GaN heterostructure in different bending conditions. By bending up, 2DHG is formed to perform the device function as HHMTs. Without bending, two-dimensional electron gas (2DEG) is induced and the transistors perform as high electron mobility transistors (HEMTs). This unique property can be used in complementary integrated circuits for high-power and high-temperature applications. Index Terms—simulation, 2DHG, HHMT, HEMT, bending I. INTRODUCTION IGH-hole-mobility transistors (HHMT) are a critical missing component of high-power high-temperature complementary circuits [1]. Whereas Group III-nitride (III-N) high-electron-mobility transistors (HEMTs) are matured enough for circuit and system applications, the development of III-N HHMTs has been hampered due to the difficulty in the formation of 2-dimensional hole gas (2DHG) by a triangular quantum well (QW) in valence band. Theoretical study Manuscript received April 26, 2017. This work was supported by the IT Research and Development Program of MOTIE/KEIT under Grant 10048933 (Development of epitaxial structure design and epitaxial growth system for high-voltage power semiconductors). J.-H. Ryou also acknowledges partial financial support from the Texas Center for Superconductivity at the University of Houston (TcSUH). W. Wang, Y. Huai, and S. K. Oh are with Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA. S. Shervin, J. Chen, and S. Pouladi are with Materials Science and Engineering Program, University of Houston, Houston, TX 77204, USA. H. Kim is with School of Semiconductor and Chemical Engineering and Semiconductor Physics Research Center, Chonbuk National University, Jeonju 54896, South Korea. S.-N. Lee is with Department of Nano-Optical Engineering, Korea Polytechnic University, Siheung 15073, South Korea. J.-H. Ryou is with Department of Mechanical Engineering, Materials Science and Engineering Program, and Texas Center for Superconductivity at the University of Houston (TcSUH), University of Houston, 4726 Calhoun Rd., Rm N207, Houston, TX 77204-4006, USA (email: jryou@uh.edu). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier predicted the formation of 2DHG from p-GaN/GaN/AlGaN/GaN heterostructures due to negative polarization at the GaN/AlGaN interface [2]. A sheet density of ~1.1×10 13 cm -2 was measured from the structure [3]. However, the mobility of channel was very low with ~16 cm 2 /V⋅s at 300 K possibly due to the scattering of hole by diffused Mg ions from the p-GaN layer. The 2DHG can also be formed in GaN/InGaN/GaN heterostructures [4]. In this case, channel is formed in the InGaN layer, where 2DHG experiences an alloy scattering effect. Furthermore, both the structures form 2-dimensional electron gas (2DEG) on the other side of the interface where 2DHG is formed. For example, the 2DHG is formed at the GaN/AlGaN interface and the 2DEG is formed at the AlGaN/GaN interface in the p-GaN/GaN/AlGaN/GaN heterostructure. The parasitic 2DEG has to be removed for p-channel devices. Therefore, the previously suggested structures may be useful for current spreading of base layer in III-N heterojunction bipolar transistors [5] and for higher conductivity of p-type layer in photonic devices [6], but not for III-N complementary integrated circuits. Recent development in flexible electronics enables flexible III-N visible light-emitting diodes and transistors [7]-[9]. Those studies focused on the mechanical flexibility of the devices, which is important in most applications. However, III-N flexible devices have an implication of more than just bendable devices, thanks to unique piezoelectric properties of the heterostructures. External strain by bending can change the performance characteristics and provide additional functionality of the photon emitters [10]. It can also enhance the density of 2DEG and control the operation of the HEMTs [11]. In the present study, we propose a new pathway for HHMT devices by combination of bandgap engineering and external bending strain to achieve 2DHG channel in the unintentionally doped GaN layer without parasitic 2DEG channel formation, which was not possible from previously suggested structures. We show via numerical modeling that the controlled bending of selected III-N heterostructures can induce only 2DHG in a GaN channel layer. Moreover, we propose an operation of complementary integrated circuit from the same III-N heterostructure with different bending conditions. II. DEVICE STRUCTURE AND SIMULATION The flexible device in this study has a typical layer scheme consisting of an AlGaInN Schottky barrier layer (20 nm) and a GaN layer (1 μm). The difference from the conventional Weijie Wang, Shahab Shervin, Student Member, IEEE, Seung Kyu Oh, Jie Chen, Yang Huai, Sara Pouladi, Hyunsoo Kim, Sung-Nam Lee, and Jae-Hyun Ryou, Senior Member, IEEE Flexible AlGaInN/GaN Heterostructures for High-Hole-Mobility Transistors H