Growth uniformity in selective area epitaxy of algan/gan heterostructures for the application in semiconductor devices

Abstract

The design of modern semiconductor devices often requires the fabrication of threedimensional (3D) structures to integrate microelectronic components with photonic, micromechanical, or sensor systems within one semiconductor substrate. It is a technologically challenging task, as a strictly defined profile of the device structure is obligatory. This can be achieved either by chemical etching or selective deposition on a masked substrate. In this paper, the growth uniformity of AlGaN/GaN heterostructures during selective-area metalorganic vapour-phase epitaxy (SA-MOVPE) was studied. Such structures are typically used in order to fabricate high-electron-mobility transistors (HEMT). The semiconductor material was deposited through 200 µm long stripe-shaped open windows in a SiO2 mask on GaN/sapphire templates. The window width was varied from 5 µm to 160 µm, whereas mask width separating particular windows varied from 5 µm to 40 µm. The experiment was repeated for three samples differing in GaN layer thickness: 150 nm, 250 nm, and 500 nm. Based on theoretical models of the selective growth, a sufficiently uniform thickness of epitaxially grown AlGaN/GaN heterostructure has been achieved by selecting the window half-width that is smaller than the diffusion length of the precursor molecules. A Ga diffusion length of 15 µm was experimentally extracted by measuring the epitaxial material agglomeration in windows in the dielectric mask. Measurements were conducted while using optical profilometry.