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Recent advances and challenges in p-type doping of InN and InN-based novel nanostructures

Akihiko Yoshikawa 1Yoshihiro Ishitani 1Xinqiang Wang 2

1. Graduate School of Electrical and Electronic Engineering, Chiba University,, 1-33 Yayoi-cho, Inage-ku, Chiba, Chiba 2638522, Japan
2. State Key Lab of Artificial Microstruct. and Mesoscopic Physics, School of Physics, Peking Univ., Beijing 100871, China


InN is still the least studied material among III-nitrides and there are several problems to be overcome for better understanding of its material properties and also for its device application. Bonding between In and N is weaker and longer than those for GaN and/or AlN, and this results in large mismatches for InN in both lattice parameters and optimum epitaxy temperatures among III-nitrides. Another important issue for InN epitaxy is a big expected difficulty in achieving p-type conduction, because the Fermi level stabilized energy for InN is located inside the conduction band, resulting in easy introduction of donor levels together with high density surface electrons

In this paper, we report the latest advances in InN epitaxy and material control paying special attention to the following two important issues:
  1) P-type doping of InN and InGaN: Reduction in the residual donors/defects concentration and successful p-type doping, together with accompanying problems arising from Mg-acceptor doping as well as their very special characterization methods inherent to InN properties.
 2) Novel InN/GaN MQWs and very detailed in-situ epitaxy analyses with SE (spectroscopic ellipsometry): Proposal, realization and characterization of novel InN/GaN MQWs consisting of around 1ML-thick InN wells in GaN matrix, together with in-situ and real-time SE characterization of self-limiting and self-ordering deposition processes resulting in 2ML, 1ML, and fractional ML InN wells in GaN matrix at extremely high temperatures under the In-polarity growth regime.

For achieving p-type conductivity in InN and In-rich InGaN ternary alloys, on the basis of careful understanding on the residual donors in unintentionally n-type doped high-quality InN, we have achieved successful p-type doping of InN after a systematic doping study for very wide range [Mg]s. Edge-component threading dislocation density in typical InN epilayers grown on GaN is about 1010 cm-2 which is originating from their large lattice mismatch. Edge-type dislocations induce donor levels above the conduction band bottom in InN and they are one of the residual donors in the orders of 3.5x1017 cm-3 density. Successful p-type doping of InN was achieved for Mg doping levels from 1018 to about 3x1019 cm-3. It was found that overdoped Mg’s introduce new donors in InN resulting in n-type conduction. We analyzed the behaviors of vacancy-type defects in those InN samples with different Mg concentrations by using positron annihilation experiments/analyses, and it was confirmed that complex defects including In and multiple-N vacancies are responsible for newly introduced donors in Mg-overdoped InN samples. It was also found that the polarity inversion from In-polarity to N-polarity took place for Mg-overdoped InN samples, though the polarity was kept unchanged in N-polarity growth in very wide Mg concentrations.

As for the novel InN/GaN MQWs, InN-based QWs consisting of coherent 1ML-thick InN wells embedded in GaN matrix were proposed and fabricated. It was confirmed that very fine structure InN QWs were fabricated by self-limiting growth mode under In-polarity growth regime at remarkably higher growth temperatures up to 690 oC. From the detailed deposition-analyses of In metal as well as InN with using SE in wavelengths from 250 nm to 1700 nm, it was found that both In and/or InN deposition was self-limited to 2ML or below at such high temperatures. Their optical properties are determined by GaN-excitons localized at InN wells. Experimental LED/LD structures were fabricated and it was confirmed that QCSE was ultimately reduced due to ultimately thin 1ML InN wells.


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Presentation: Keynote lecture at E-MRS Fall Meeting 2009, Symposium A, by Akihiko Yoshikawa
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-11 22:11
Revised:   2009-06-07 00:44