Impurity reduction in lightly doped n-type gallium nitride layer grown via halogen-free vapor-phase epitaxy

Author:

Kimura T.1ORCID,Shimazu H.1,Kataoka K.1ORCID,Itoh K.1ORCID,Narita T.1ORCID,Uedono A.2ORCID,Tokuda Y.3,Tanaka D.4,Nitta S.4ORCID,Amano H.4ORCID,Nakamura D.1ORCID

Affiliation:

1. Toyota Central R&D Labs., Inc 1 ., Nagakute, Aichi 480-1192, Japan

2. Division of Applied Physics, Faculty of Pure and Applied Science, University of Tsukuba 2 , Tsukuba, Ibaraki 305-8573, Japan

3. Aichi Institute of Technology 3 , Toyota, Aichi 470-0392, Japan

4. Institute of Materials and Systems for Sustainability, Nagoya University 4 , Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan

Abstract

The development of gallium nitride (GaN) vertical-type metal-oxide-semiconductor field-effect transistors and p–i–n diode devices has gathered increasing attention. These devices require an n-type drift layer with a low doping level of 1016 cm−3 or less, minimized point defects inhibiting electron conduction, and a layer approximately 10 μm thick. Therefore, a practical method with a growth rate of at least several tens of μm/h and impurity concentrations of less than 1015 cm−3, except for that of dopants, is necessary. Halogen-free vapor-phase epitaxy (HF-VPE) has a high growth rate suitable for fabricating thick drift layers and utilizes a simple reaction between Ga vapor and ammonia gas (without a corrosive halogen gas), resulting in lower impurity levels. Herein, we eliminated the quartz content from the high-temperature zone to reduce the excess unintentional Si doping and identified that the nitrile gloves used for the growth preparation are other impurity contamination sources. We obtained a lightly n-type ([Si]=∼1016 cm−3) GaN layer, in which C, O, B, Fe, Mg, Al, Ca, Cr, Zn, Ni, Mn, and Ti impurity contents were below the detection limits of secondary ion mass spectrometry. Deep-level transient spectroscopy revealed that electron traps at EC − 0.26 and at EC − 0.59 eV were 2.7 × 1013 and 5.2 × 1014 cm−3, respectively. Moreover, the Hall effect analysis showed the acceptor-type defect-compensating donor content as approximately 2.7 × 1015 cm−3, resulting in a high electron mobility of HF-VPE GaN in the 30–710 K temperature range. Furthermore, we identified the Ca impurity as a deep acceptor, another killer defect leading to mobility collapse.

Funder

Ministry of Education, Culture, Sports, Science and Technology

Publisher

AIP Publishing

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