Influence of lattice constants of GaN and InGaN on npn-Type GaN/InGaN heterojunction bipolar transistors

Toshiki Makimoto*, Takatoshi Kido, Kazuhide Kumakura, Yoshitaka Taniyasu, Makoto Kasu, Nobuo Matsumoto

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


We investigated the a- and c-axis lattice constants of GaN buffer and 180-nm-thick p-InGaN layers grown on SiC and sapphire substrates using reciprocal space mapping of the X-ray diffraction intensity. It was found that the a-axis lattice constant of the GaN buffer layer on a SiC substrate is larger than those of unstrained GaN and a GaN buffer layer on a sapphire substrate. As a result, the p-InGaN layer on GaN/SiC is fully strained even at the In mole fraction of 9.0% where that on GaN/sapphire is relaxed. This result means that fewer defects are generated in p-InGaN on GaN/SiC at higher In mole fractions. This is another advantage of SiC substrate for npn-type GaN/InGaN heterojunction bipolar transistors, in addition to its high thermal conductivity. The collector current density dependence of current gain shows the ideality factor of 2 for GaN/InGaN HBTs on both SiC and sapphire substrates. This is ascribed to the recombination current at the emitter-base interface, which arises from the threading dislocations generated at the interface between the substrate and nitride buffer layer.

Original languageEnglish
Pages (from-to)3395-3397
Number of pages3
JournalJapanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers
Issue number4 B
Publication statusPublished - 2006 Apr 25
Externally publishedYes


  • GaN
  • HBT
  • Lattice constant
  • P-InGaN
  • SIC
  • Sapphire
  • Strain

ASJC Scopus subject areas

  • Engineering(all)
  • Physics and Astronomy(all)


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