Mechanism for Forming Quantum-Size AlGaN/GaN/InGaN/GaN Heterostructure Layers

Abstract

The use of silicon in optoelectronic elements and microwave devices is limited by its electrical properties. In this range of application, silicon is replaced by wider-gap materials, e.g., GaN, AlN, InN, and solid solutions based on them. This allows highly efficient devices, including light-emitting diodes and photodetectors operating in a wide radiation spectral range, to be fabricated. In addition, GaN-based materials have been successfully used in designing high-power microwave devices, in particular, transistors with highly mobile electrons operating at high temperatures. We discuss specific features of the technology for fabricating active layers in the AlGaN/GaN/InGaN/GaN heterostructures with the use of metalorganic compounds. The initial substances used are ultra-pure ammonia NH₃ and gallium, aluminum, and indium metalorganic compounds in the trimethyl form. The temperature dependence of the epitaxial GaN layer growth rate is investigated. This dependence is shown to be weak in a wide temperature range. The importance of adsorption processes occurring on the growth surfaces is confirmed. Thermodynamical analysis of the regularities of the investigated process is carried out to simulate the process and establish the conditions for forming GaN-based solid solutions. It is shown that during the formation of Ga_1 – xIn_xN solid solutions in the high-temperature region the attainable InN content is not higher than 0.4 mole fractions. As the growth temperature decreases to 600°С, the conditions for incorporating In in the solid solution are noticeably improved and the InN concentration increases to 0.9 mole fractions. It is demonstrated that growing the GaAlN solid solutions in a wide temperature range makes it possible to obtain the AlN content ranging from 0.1 to 0.9 mole fractions. The experimental investigations are confirmed by the calculations. Therefore, when growing the Ga_1 – xIn_xN quantum well layers in the active heterostructural area for commercial blue light-emitting diode chips with an indium content of х = 0.1–0.15, the growth temperature should be reduced. At low temperatures, however, it is difficult to grow epitaxial layers with a high crystal quality.