Optical micrograph (image width of 60μm) of
(11.2) oriented GaN layer grown on m-plane sapphire.
Larry Leung, PhD, Product Manager, HVPE Products
Semi-Polar (11.2) GaN on m-Plane Sapphire by HVPE to Increase Optoelectronic Device Performance
In the past decade, Group III-nitride materials have been widely used for visible and ultraviolet light emitting diodes and blue, violet laser diodes. Most of these optoelectronic devices are typically fabricated on the conventional polar (0001) c-plane oriented substrate materials.
Devices grown on the polar substrate orientation suffer undesirable spontaneous and piezoelectric polarization that give rise to significant band bending in the quantum well, hence reducing the radiative recombination efficiency and lowering the device performance.
Therefore, growth of GaN-related devices along semi-polar and nonpolar directions has been studied intensely in order to diminish these polarization effects. Recently, the technical team at Oxford Instruments-TDI, led by Dr. Alexander Usikov, has made significant progress in solving this problem. Using hydride vapour phase epitaxy (HVPE), the team has grown high quality, semi-polar (11.2) oriented GaN on (10.0) m-plane sapphire with an intermediate layer between the sapphire substrate and the GaN layer.
The semi-polar (11.2) GaN layers were grown in the temperature range from 930 to 1050ºC in an inert argon ambient at atmospheric pressure. Gallium and aluminium were used as metallic source materials and hydrogen chloride (HCl) and ammonia (NH3) as the active gases for the HVPE process. The epitaxial growth of GaN was performed at approximately 60µm/per hour using an intermediate layer deposited on m-plane sapphire followed by an undoped GaN layer. The growth procedure results in high quality, semi-polar GaN layer with thickness up to 30µm.
The GaN layer exhibits smooth surface morphology with some macroscopic surface modulation. The figure shows the optical micrograph (image width of 60µm) of (11.2) oriented GaN layer grown on m-plane sapphire.
Atomic force microscope (AFM) results show the rms surface roughness of 3.7nm for a 2µm x 2µm scan.
This new material has generated much interest within the nitride R&D community.
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