Growth of GaN/InGaN Films and Heterostructures Via Super-Atmospheric MOCVD
Authors: Krause John Robert , Stokes Edward Brittain 
Published: February 2020

The beneficial material properties of Wide-Bandgap semiconductors have allowed them to find utility in a number of modern industries. GaN based devices particularly have found acceptance in both the solid-state lighting[1] and power-electronics[2].
In the realm of lighting applications, III-Nitride based devices theoretically have a bandgap capable of extending over the range of 0.7 eV to 3.39eV. However, it has proven difficult to realize devices with high crystalline quality and bandgaps that fall within the 2.25 to 2.1 eV range. This problem is partially due to the mismatch in lattice constant between GaN and Indium-Rich GaN crystals. Additionally, during the growth process, Indium desorbs from the crystal surface at the temperatures necessary for high-quality GaN growth[3].
This research chronicles the on-going efforts to utilize super-atmospheric growth conditions to alleviate these, among other, fundamental issues in the growth of Indium-Rich GaN heterostructures. Experiments are conducted within a unique reactor with internal geometry optimized for high-pressure growth. The reactor features an input geometry intended to reduce gas-phase reactions via physical separation of the group III and group V precursors. Furthermore, the chamber walls and exhaust are optimized to encourage laminar flow throughout the reactor.[4]
Experiments are constructed to analyze the effect of several growth parameters on the resulting multiple-quantum-well heterostructure. Results are analyzed in terms of internal quantum efficiency measured by the temperature dependence of photo luminescent emission.
To reach an acceptable baseline of MQW performance several early growth modifications were analyzed. Among these were the introduction of growth-interruptions at Barrier/Well interfaces, Indium pre-deposition and modification of TMIn waterbath temperature. Initial experimentation indicated that the PL peak red-shifts with increasing TMIn temperature as would be expected. PL intensity is also observed to increase at room temperature when growth interruptions are included, presumably due to an enhanced abruptness of QW/Barrier interfaces. See Figure 1.
Furthermore, CFD simulations indicated that susceptor rotational speed could lead to an increase in gas flow velocity in the vicinity of the sample, possibly leading to a decreased boundary layer thickness. Experimentation showed a consistent red-shift of PL with increasing rotation rate that is not readily accountable by the very slight change in growth rates between samples. See Figure 2.
Additional ongoing experiments and their results are presented and discussed in the complete body of work.
[1] P. Smallwood, in Strategies in Light Conference, Las Vegas, NV, February 2015
[2] Mishra, Umesh K., et al. "GaN-based RF power devices and amplifiers."Proceedings of the IEEE 96.2 (2008): 287-305.
[3] Koukitu, A., et al. "THERMODYNAMIC ANALYSIS OF THE MOVPE GROWTH OF IN X GA 1-X N." Journal of Crystal Growth 170 (1997): 306-311.
[4] Melton, Andrew G., et al. "Superatmospheric MOCVD Reactor Design for High Quality InGaN Growth." ECS Transactions 45.7 (2012): 73-77.

Figure 1