"WM"-Shaped Growth of GaN on Patterned Sapphire Substrates

TL;DR

This study investigates how varying growth temperatures in metal organic vapor phase epitaxy influence the shape and growth mode of GaN on patterned sapphire substrates, enabling control over V-pit formation and surface orientation.

Contribution

It demonstrates temperature-dependent transition between 3D and 2D growth modes of GaN on patterned sapphire, allowing control over V-pit size and surface orientation.

Findings

Lower temperature (~950°C) induces 3D V-pit-shaped GaN growth.

Higher temperature (~1000°C) transitions growth to 2D, reducing V-pit size.

Growth mode and surface orientation can be controlled by temperature and time.

Abstract

In metal organic vapor phase epitaxy of GaN, the growth mode is sensitive to reactor temperature. In this study, V-pit-shaped GaN has been grown on normal c-plane cone-patterned sapphire substrate by decreasing the growth temperature of high-temperature-GaN to around 950 oC, which leads to the 3-dimensional growth of GaN. The so-called "WM" well describes the shape that the bottom of GaN V-pit is just right over the top of sapphire cone, and the regular arrangement of V-pits follows the patterns of sapphire substrate strictly. Two types of semipolar facets (1101) and (1122) expose on sidewalls of V-pits. Furthermore, by raising the growth temperature to 1000 oC, the growth mode of GaN can be transferred to 2-demonsional growth. Accordingly, the size of V-pits becomes smaller and the area of c-plane GaN becomes larger, while the total thickness of GaN keeps almost unchanged during this process. As long as the 2-demonsional growth lasts, the V-pits will disappear and only flat c-plane GaN remains. This means the area ratio of c-plane and semipolar plane GaN can be controlled by the duration time of 2-demonsional growth.