Buffer Layer Doping Concentration Measurement Using VT-VSUB Characteristics of GaN HEMT with p-GaN Substrate Layer

Cheng-Yu HU  Katsutoshi NAKATANI  Hiroji KAWAI  Jin-Ping AO  Yasuo OHNO  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E93-C   No.8   pp.1234-1237
Publication Date: 2010/08/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E93.C.1234
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Heterostructure Microelectronics with TWHM 2009)
Category: GaN-based Devices
Keyword: 
AlGaN/GaN HFET,  VT-VSUB,  substrate bias,  p-GaN,  SIMS,  

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Summary: 
To improve the high voltage performance of AlGaN/GaN heterojunction field effect transistors (HFETs), we have fabricated AlGaN/GaN HFETs with p-GaN epi-layer on sapphire substrate with an ohmic contact to the p-GaN (p-sub HFET). Substrate bias dependent threshold voltage variation (VT-VSUB) was used to directly determine the doping concentration profile in the buffer layer. This VT-VSUB method was developed from Si MOSFET. For HFETs, the insulator is formed by epitaxially grown and heterogeneous semiconductor layer while for Si MOSFETs the insulator is amorphous SiO2. Except that HFETs have higher channel mobility due to the epitaxial insulator/semiconductor interface, HFETs and Si MOSFETs are basically the same in the respect of device physics. Based on these considerations, the feasibility of this VT-VSUB method for AlGaN/GaN HFETs was discussed. In the end, the buffer layer doping concentration was measured to be 21017 cm-3, p-type, which is well consistent with the Mg concentration obtained from secondary ion mass spectroscopy (SIMS) measurement.