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.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/18455 must be provided.

1. Polarity determination of InN by using circular photogalvanic effect
2. Effects of threading dislocations and other defects on reduction of band-edge photoluminescence in n-InN films
3. Epitaxy Control and Characterization of InN, InN-based Ternary Alloys, and Their MQW-structures