Magneto-transport and effective mass of two-dimensional hole gases in modulation-doped and undoped GeSn/Ge heterostructures

Chia-Tse Tai^1*, Po-Yuan Chiu¹, Yen Chuang¹, Chia-You Liu¹, Tz-Ming Wang¹, Cheng-Yu Lin², C. Thomas Harris³, Tzu-Ming Lu³, Jiun-Yun Li^1,2,4

¹Graduate Institute of Electronics Engineering, National Taiwan University, Taipei, Taiwan
²Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan
³Center for Integrated Nanotechnologies, Sandia National Laboratories, New Mexico, USA
⁴Taiwan Semiconductor Research Institute, Hsinchu, Taiwan

* Presenter:Chia-Tse Tai, email:r07943077@ntu.edu.tw

In this work, carrier transport and effective masses of two-dimensional hole gases (2DHGs) in both modulation-doped and undoped GeSn/Ge heterostructures are investigated. GeSn and Ge epitaxial layers were grown by chemical vapor deposition and Hall bar devices were fabricated for magnetoresistance measurements at low temperatures. The Sn fractions of GeSn alloys are 6%, 9%, and 11%. The hole density in the modulation-doped devices is 3 x10¹¹ cm^-2 with a peak mobility of 2.6x10⁴ cm²/V-s at 4 K. For the undoped devices, the carrier density of 2DHGs capacitively modulated by top gating increases first and saturates at 3.3x10¹¹ cm^-2 due to surface tunneling. The peak mobility for the undoped devices is 1.9x10⁴ cm²/ V-s.
Shubnikov-de Haas (SdH) oscillations and quantum Hall plateaus were observed at T=1.2~10 K for all devices. Effective mass extracted from the temperature-dependent SdH oscillations is 0.10m₀ (0.08m₀ ) for the modulation-doped device with Sn fractions of 6% (11%). We obtain a linear relation between the mass and carrier density using the undoped devices. Simulations of GeSn band structures were performed by a combination of empirical pseudopotential method (EPM) and 6-band k∙p method to compare the measured effective masses. The simulation results show that the effective mass decreases with the Sn fraction of GeSn alloys, which is consistent with our experiment results.
This work at NTU was supported by MOST (107-2112-M-002-014- and 108-2112-M-002-011-) and was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. Department of Energy (DOE), Office of Basic Energy Sciences user facility. Sandia National Labs is managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a subsidiary of Honeywell International, Inc., for the U.S. DOE’s National Nuclear Security Administration under contract DE-NA0003525. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government.

Keywords: GeSn/Ge heterostructures, 2DHGs, effective mass, magneto-transport, Shubnikov-de Haas oscillation