Growth of High-Quality AlN and AlN/GaN/AlN Heterostructure on Sapphire Substrate

Abstract

Metalorganic chemical vapor deposition (MOCVD) growth of AlN on sapphire substrates was investigated, with the aim of device quality AlN/GaN/AlN double heterostructures. Growth temperature as high as 1300° C was required to obtain AlN epitaxial layers with sharp X-ray diffraction peaks. By growing AlN at the high growth temperature, residual stress at the heterointerface was effectively reduced. The AlN epitaxial layers with smooth surfaces were grown using a low V/III ratio together with the high growth temperature. AlN/GaN/AlN double heterostructures with appropriate layer thicknesses for DH lasers and flat heterointerfaces were grown on sapphire substrates.

Digitally Alloyed Modulated Precursor Flow Epitaxial Growth of Ternary AlGaN with Binary AlN and GaN Sub-Layers and Observation of Compositional Inhomogeneity

“…However, the growth of such layers by conventional metalorganic chemical vapor deposition (MOCVD) (especially on a foreign substrate via strained heteroepitaxy) often suffers from a rough surface morphology and poor crystalline quality due to the lattice and thermal expansion mismatches between the Al x Ga 1Àx N heteroepitaxial layer and the substrate, severe adduct formation between trimethylaluminum (TMAl) and ammonia (NH 3 ), 4 and limited migration (a short diffusion length) of adatoms (or surface species) of Al on a growing surface. High growth temperatures over 1300°C 5,6 and low growth pressures of 30-50 Torr 7 have been employed to enhance the surface migration of Al adatom species and to suppress parasitic gas-phase reactions (adduct formation) between TMAl and NH 3 . Increasing the growth temperature above 1300°C is, however, in many cases, restricted by the capability of the heating element of a reactor system, especially for resistive heating, and limited by low sticking coefficients of other column III elements such as gallium and indium at very high temperature for the growth of ternary or quaternary Al-containing alloys.…”

Growth of high‐quality AlN at high growth rate by high‐temperature MOVPE

“…The high temperature growth of AlN films is expected to be effective in improving crystalline quality and surface morphology because surface migration of Al-species would increase at high temperatures. There are few reports on AlN growth at high temperatures on the order of 1350 °C [5,6] due probably to the instrumental limitation.In this study, we made an attempt to systematically study the high-temperature growth of AlN on (0001) sapphire substrates. The temperatures are in the range from 1200 to 1500 °C.…”

High‐quality AlN epitaxial films on (0001)‐faced sapphire and 6H‐SiC substrate

“…We have already realized high-quality AlN epitaxial films on a (0001)-faced sapphire substrate and we proposed that they are one of the most promising templates for high-quality GaN and AlGaN growth [1][2][3][4][5]. It is predicted that higher AlN molar fraction of underlayers (AlN) than overgrown GaN or AlGaN layers can induce compressive stress in the overgrown layers and that the compressive stress has effects in restraint of crack generation and reduction of dislocation density [1,3,6]. In addition, AlN epitaxial films on a sapphire substrate are transparent in ultraviolet region and the templates are promising for high-external-quantum-efficiency ultraviolet optical devices [7].…”